- REST Endpoints
- Remoting and Web Services
- Enterprise JavaBeans (EJB) Integration
- JMS (Java Message Service)
- JMX
- Task Execution and Scheduling
- Cache Abstraction
- Understanding the Cache Abstraction
- Declarative Annotation-based Caching
- JCache (JSR-107) Annotations
- Declarative XML-based Caching
- Configuring the Cache Storage
- Plugging-in Different Back-end Caches
- How can I Set the TTL/TTI/Eviction policy/XXX feature?
This part of the reference documentation covers Spring Framework’s integration with a number of technologies.
The Spring Framework provides two choices for making calls to REST endpoints:
-
RestTemplate: The original Spring REST client with a synchronous, template method API. -
WebClient: a non-blocking, reactive alternative that supports both synchronous and asynchronous as well as streaming scenarios.
|
Note
|
As of 5.0 the RestTemplate is in maintenance mode, with only minor requests for
changes and bugs to be accepted going forward. Please, consider using the
WebClient which offers a more modern API and
supports sync, async, and streaming scenarios.
|
The RestTemplate provides a higher level API over HTTP client libraries. It makes it
easy to invoke REST endpoints in a single line. It exposes the following groups of
overloaded methods:
| Method group | Description |
|---|---|
|
Retrieves a representation via GET. |
|
Retrieves a |
|
Retrieves all headers for a resource by using HEAD. |
|
Creates a new resource by using POST and returns the |
|
Creates a new resource by using POST and returns the representation from the response. |
|
Creates a new resource by using POST and returns the representation from the response. |
|
Creates or updates a resource by using PUT. |
|
Updates a resource by using PATCH and returns the representation from the response.
Note that the JDK |
|
Deletes the resources at the specified URI by using DELETE. |
|
Retrieves allowed HTTP methods for a resource by using ALLOW. |
|
More generalized (and less opinionated) version of the preceding methods that provides extra
flexibility when needed. It accepts a These methods allow the use of |
|
The most generalized way to perform a request, with full control over request preparation and response extraction through callback interfaces. |
The default constructor uses java.net.HttpURLConnection to perform requests. You can
switch to a different HTTP library with an implementation of ClientHttpRequestFactory.
There is built-in support for the following:
-
Apache HttpComponents
-
Netty
-
OkHttp
For example, to switch to Apache HttpComponents, you can use the following:
RestTemplate template = new RestTemplate(new HttpComponentsClientHttpRequestFactory());Each ClientHttpRequestFactory exposes configuration options specific to the underlying
HTTP client library — for example, for credentials, connection pooling, and other details.
|
Tip
|
Note that the java.net implementation for HTTP requests can raise an exception when
accessing the status of a response that represents an error (such as 401). If this is an
issue, switch to another HTTP client library.
|
Many of the RestTemplate methods accept a URI template and URI template variables,
either as a String variable argument, or as Map<String,String>.
The following example uses a String variable argument:
String result = restTemplate.getForObject(
"https://example.com/hotels/{hotel}/bookings/{booking}", String.class, "42", "21");The following example uses a Map<String, String>:
Map<String, String> vars = Collections.singletonMap("hotel", "42");
String result = restTemplate.getForObject(
"https://example.com/hotels/{hotel}/rooms/{hotel}", String.class, vars);Keep in mind URI templates are automatically encoded, as the following example shows:
restTemplate.getForObject("https://example.com/hotel list", String.class);
// Results in request to "https://example.com/hotel%20list"You can use the uriTemplateHandler property of RestTemplate to customize how URIs
are encoded. Alternatively, you can prepare a java.net.URI and pass it into one of
the RestTemplate methods that accepts a URI.
For more details on working with and encoding URIs, see URI Links.
You can use the exchange() methods to specify request headers, as the following example shows:
String uriTemplate = "https://example.com/hotels/{hotel}";
URI uri = UriComponentsBuilder.fromUriString(uriTemplate).build(42);
RequestEntity<Void> requestEntity = RequestEntity.get(uri)
.header("MyRequestHeader", "MyValue")
.build();
ResponseEntity<String> response = template.exchange(requestEntity, String.class);
String responseHeader = response.getHeaders().getFirst("MyResponseHeader");
String body = response.getBody();You can obtain response headers through many RestTemplate method variants that return
ResponseEntity.
Objects passed into and returned from RestTemplate methods are converted to and from raw
content with the help of an HttpMessageConverter.
On a POST, an input object is serialized to the request body, as the following example shows:
URI location = template.postForLocation("https://example.com/people", person);
You need not explicitly set the Content-Type header of the request. In most cases,
you can find a compatible message converter based on the source Object type, and the chosen
message converter sets the content type accordingly. If necessary, you can use the
exchange methods to explicitly provide the Content-Type request header, and that, in
turn, influences what message converter is selected.
On a GET, the body of the response is deserialized to an output Object, as the following example shows:
Person person = restTemplate.getForObject("https://example.com/people/{id}", Person.class, 42);
The Accept header of the request does not need to be explicitly set. In most cases,
a compatible message converter can be found based on the expected response type, which
then helps to populate the Accept header. If necessary, you can use the exchange
methods to provide the Accept header explicitly.
By default, RestTemplate registers all built-in
message converters, depending on classpath checks that help
to determine what optional conversion libraries are present. You can also set the message
converters to use explicitly.
The spring-web module contains the HttpMessageConverter contract for reading and
writing the body of HTTP requests and responses through InputStream and OutputStream.
HttpMessageConverter instances are used on the client side (for example, in the RestTemplate) and
on the server side (for example, in Spring MVC REST controllers).
Concrete implementations for the main media (MIME) types are provided in the framework
and are, by default, registered with the RestTemplate on the client side and with
RequestMethodHandlerAdapter on the server side (see
Configuring Message Converters).
The implementations of HttpMessageConverter are described in the following sections.
For all converters, a default media type is used, but you can override it by setting the
supportedMediaTypes bean property. The following table describes each implementation:
| MessageConverter | Description |
|---|---|
|
An |
|
An |
|
An |
|
An |
|
An |
|
An |
|
An |
|
An |
You can specify a Jackson JSON View to serialize only a subset of the object properties, as the following example shows:
MappingJacksonValue value = new MappingJacksonValue(new User("eric", "7!jd#h23"));
value.setSerializationView(User.WithoutPasswordView.class);
RequestEntity<MappingJacksonValue> requestEntity =
RequestEntity.post(new URI("https://example.com/user")).body(value);
ResponseEntity<String> response = template.exchange(requestEntity, String.class);To send multipart data, you need to provide a MultiValueMap<String, Object> whose values
may be an Object for part content, a Resource for a file part, or an HttpEntity for
part content with headers. For example:
MultiValueMap<String, Object> parts = new LinkedMultiValueMap<>();
parts.add("fieldPart", "fieldValue");
parts.add("filePart", new FileSystemResource("...logo.png"));
parts.add("jsonPart", new Person("Jason"));
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_XML);
parts.add("xmlPart", new HttpEntity<>(myBean, headers));In most cases, you do not have to specify the Content-Type for each part. The content
type is determined automatically based on the HttpMessageConverter chosen to serialize
it or, in the case of a Resource based on the file extension. If necessary, you can
explicitly provide the MediaType with an HttpEntity wrapper.
Once the MultiValueMap is ready, you can pass it to the RestTemplate, as show below:
MultiValueMap<String, Object> parts = ...;
template.postForObject("https://example.com/upload", parts, Void.class);If the MultiValueMap contains at least one non-String value, the Content-Type is set
to multipart/form-data by the FormHttpMessageConverter. If the MultiValueMap has
String values the Content-Type is defaulted to application/x-www-form-urlencoded.
If necessary the Content-Type may also be set explicitly.
Spring provides support for remoting with various technologies. The remoting support eases the development of remote-enabled services, implemented via Java interfaces and objects as input and output. Currently, Spring supports the following remoting technologies:
-
Java Web Services: Spring provides remoting support for web services through JAX-WS.
-
AMQP: Remoting via AMQP as the underlying protocol is supported by the separate Spring AMQP project.
|
Warning
|
As of Spring Framework 5.3, support for several remoting technologies is now deprecated for security reasons and broader industry support. Supporting infrastructure will be removed from Spring Framework for its next major release. |
The following remoting technologies are now deprecated and will not be replaced:
-
Remote Method Invocation (RMI): Through the use of
RmiProxyFactoryBeanandRmiServiceExporter, Spring supports both traditional RMI (withjava.rmi.Remoteinterfaces andjava.rmi.RemoteException) and transparent remoting through RMI invokers (with any Java interface). -
Spring HTTP Invoker (Deprecated): Spring provides a special remoting strategy that allows for Java serialization though HTTP, supporting any Java interface (as the RMI invoker does). The corresponding support classes are
HttpInvokerProxyFactoryBeanandHttpInvokerServiceExporter. -
Hessian: By using Spring’s
HessianProxyFactoryBeanand theHessianServiceExporter, you can transparently expose your services through the lightweight binary HTTP-based protocol provided by Caucho. -
JMS (Deprecated): Remoting via JMS as the underlying protocol is supported through the
JmsInvokerServiceExporterandJmsInvokerProxyFactoryBeanclasses in thespring-jmsmodule.
While discussing the remoting capabilities of Spring, we use the following domain model and corresponding services:
public class Account implements Serializable {
private String name;
public String getName(){
return name;
}
public void setName(String name) {
this.name = name;
}
}public interface AccountService {
public void insertAccount(Account account);
public List<Account> getAccounts(String name);
}// the implementation doing nothing at the moment
public class AccountServiceImpl implements AccountService {
public void insertAccount(Account acc) {
// do something...
}
public List<Account> getAccounts(String name) {
// do something...
}
}This section starts by exposing the service to a remote client by using RMI and talk a bit about the drawbacks of using RMI. It then continues with an example that uses Hessian as the protocol.
Remoting via AMQP as the underlying protocol is supported in the Spring AMQP project. For further details please visit the {doc-root}/spring-amqp/docs/current/reference/html/#remoting[Spring Remoting] section of the Spring AMQP reference.
|
Note
|
Auto-detection is not implemented for remote interfaces. The main reason why auto-detection of implemented interfaces does not occur for remote
interfaces is to avoid opening too many doors to remote callers. The target object might
implement internal callback interfaces, such as Offering a proxy with all interfaces implemented by the target usually does not matter in the local case. However, when you export a remote service, you should expose a specific service interface, with specific operations intended for remote usage. Besides internal callback interfaces, the target might implement multiple business interfaces, with only one of them intended for remote exposure. For these reasons, we require such a service interface to be specified. This is a trade-off between configuration convenience and the risk of accidental exposure of internal methods. Always specifying a service interface is not too much effort and puts you on the safe side regarding controlled exposure of specific methods. |
Each and every technology presented here has its drawbacks. When choosing a technology, you should carefully consider your needs, the services you expose, and the objects you send over the wire.
When using RMI, you cannot access the objects through the HTTP protocol, unless you tunnel the RMI traffic. RMI is a fairly heavy-weight protocol, in that it supports full-object serialization, which is important when you use a complex data model that needs serialization over the wire. However, RMI-JRMP is tied to Java clients. It is a Java-to-Java remoting solution.
Spring’s HTTP invoker is a good choice if you need HTTP-based remoting but also rely on Java serialization. It shares the basic infrastructure with RMI invokers but uses HTTP as transport. Note that HTTP invokers are not limited only to Java-to-Java remoting but also to Spring on both the client and the server side. (The latter also applies to Spring’s RMI invoker for non-RMI interfaces.)
Hessian might provide significant value when operating in a heterogeneous environment, because they explicitly allow for non-Java clients. However, non-Java support is still limited. Known issues include the serialization of Hibernate objects in combination with lazily-initialized collections. If you have such a data model, consider using RMI or HTTP invokers instead of Hessian.
JMS can be useful for providing clusters of services and letting the JMS broker take care of load balancing, discovery, and auto-failover. By default, Java serialization is used for JMS remoting, but the JMS provider could use a different mechanism for the wire formatting, such as XStream to let servers be implemented in other technologies.
Last but not least, EJB has an advantage over RMI, in that it supports standard role-based authentication and authorization and remote transaction propagation. It is possible to get RMI invokers or HTTP invokers to support security context propagation as well, although this is not provided by core Spring. Spring offers only appropriate hooks for plugging in third-party or custom solutions.
Spring provides full support for the standard Java web services APIs:
-
Exposing web services using JAX-WS
-
Accessing web services using JAX-WS
In addition to stock support for JAX-WS in Spring Core, the Spring portfolio also features Spring Web Services, which is a solution for contract-first, document-driven web services — highly recommended for building modern, future-proof web services.
Spring provides a convenient base class for JAX-WS servlet endpoint implementations:
SpringBeanAutowiringSupport. To expose our AccountService, we extend Spring’s
SpringBeanAutowiringSupport class and implement our business logic here, usually
delegating the call to the business layer. We use Spring’s @Autowired
annotation to express such dependencies on Spring-managed beans. The following example
shows our class that extends SpringBeanAutowiringSupport:
/**
* JAX-WS compliant AccountService implementation that simply delegates
* to the AccountService implementation in the root web application context.
*
* This wrapper class is necessary because JAX-WS requires working with dedicated
* endpoint classes. If an existing service needs to be exported, a wrapper that
* extends SpringBeanAutowiringSupport for simple Spring bean autowiring (through
* the @Autowired annotation) is the simplest JAX-WS compliant way.
*
* This is the class registered with the server-side JAX-WS implementation.
* In the case of a Jakarta EE server, this would simply be defined as a servlet
* in web.xml, with the server detecting that this is a JAX-WS endpoint and reacting
* accordingly. The servlet name usually needs to match the specified WS service name.
*
* The web service engine manages the lifecycle of instances of this class.
* Spring bean references will just be wired in here.
*/
import org.springframework.web.context.support.SpringBeanAutowiringSupport;
@WebService(serviceName="AccountService")
public class AccountServiceEndpoint extends SpringBeanAutowiringSupport {
@Autowired
private AccountService biz;
@WebMethod
public void insertAccount(Account acc) {
biz.insertAccount(acc);
}
@WebMethod
public Account[] getAccounts(String name) {
return biz.getAccounts(name);
}
}Our AccountServiceEndpoint needs to run in the same web application as the Spring
context to allow for access to Spring’s facilities. This is the case by default in Java
EE environments, using the standard contract for JAX-WS servlet endpoint deployment.
See the various Jakarta EE web service tutorials for details.
The built-in JAX-WS provider that comes with Oracle’s JDK supports exposure of web
services by using the built-in HTTP server that is also included in the JDK. Spring’s
SimpleJaxWsServiceExporter detects all @WebService-annotated beans in the Spring
application context and exports them through the default JAX-WS server (the JDK HTTP
server).
In this scenario, the endpoint instances are defined and managed as Spring beans
themselves. They are registered with the JAX-WS engine, but their lifecycle is up to
the Spring application context. This means that you can apply Spring functionality
(such as explicit dependency injection) to the endpoint instances. Annotation-driven
injection through @Autowired works as well. The following example shows how to
define these beans:
<bean class="org.springframework.remoting.jaxws.SimpleJaxWsServiceExporter">
<property name="baseAddress" value="http://localhost:8080/"/>
</bean>
<bean id="accountServiceEndpoint" class="example.AccountServiceEndpoint">
...
</bean>
...The AccountServiceEndpoint can but does not have to derive from Spring’s SpringBeanAutowiringSupport,
since the endpoint in this example is a fully Spring-managed bean. This means that
the endpoint implementation can be as follows (without any superclass declared — and Spring’s @Autowired configuration annotation is still honored):
@WebService(serviceName="AccountService")
public class AccountServiceEndpoint {
@Autowired
private AccountService biz;
@WebMethod
public void insertAccount(Account acc) {
biz.insertAccount(acc);
}
@WebMethod
public List<Account> getAccounts(String name) {
return biz.getAccounts(name);
}
}Oracle’s JAX-WS RI, developed as part of the GlassFish project, ships Spring support as part of its JAX-WS Commons project. This allows for defining JAX-WS endpoints as Spring-managed beans, similar to the standalone mode discussed in the previous section — but this time in a Servlet environment.
|
Note
|
This is not portable in a Jakarta EE environment. It is mainly intended for non-EE environments, such as Tomcat, that embed the JAX-WS RI as part of the web application. |
The differences from the standard style of exporting servlet-based endpoints are that
the lifecycle of the endpoint instances themselves are managed by Spring and that there
is only one JAX-WS servlet defined in web.xml. With the standard Jakarta EE style (as
shown earlier), you have one servlet definition per service endpoint, with each endpoint
typically delegating to Spring beans (through the use of @Autowired, as shown earlier).
See https://jax-ws-commons.java.net/spring/ for details on setup and usage style.
Spring provides two factory beans to create JAX-WS web service proxies, namely
LocalJaxWsServiceFactoryBean and JaxWsPortProxyFactoryBean. The former can
return only a JAX-WS service class for us to work with. The latter is the full-fledged
version that can return a proxy that implements our business service interface.
In the following example, we use JaxWsPortProxyFactoryBean to create a proxy for the
AccountService endpoint (again):
<bean id="accountWebService" class="org.springframework.remoting.jaxws.JaxWsPortProxyFactoryBean">
<property name="serviceInterface" value="example.AccountService"/> (1)
<property name="wsdlDocumentUrl" value="http://localhost:8888/AccountServiceEndpoint?WSDL"/>
<property name="namespaceUri" value="https://example/"/>
<property name="serviceName" value="AccountService"/>
<property name="portName" value="AccountServiceEndpointPort"/>
</bean>-
Where
serviceInterfaceis our business interface that the clients use.
wsdlDocumentUrl is the URL for the WSDL file. Spring needs this at startup time to
create the JAX-WS Service. namespaceUri corresponds to the targetNamespace in the
.wsdl file. serviceName corresponds to the service name in the .wsdl file. portName
corresponds to the port name in the .wsdl file.
Accessing the web service is easy, as we have a bean factory for it that exposes it as
an interface called AccountService. The following example shows how we can wire this
up in Spring:
<bean id="client" class="example.AccountClientImpl">
...
<property name="service" ref="accountWebService"/>
</bean>From the client code, we can access the web service as if it were a normal class, as the following example shows:
public class AccountClientImpl {
private AccountService service;
public void setService(AccountService service) {
this.service = service;
}
public void foo() {
service.insertAccount(...);
}
}|
Note
|
The above is slightly simplified in that JAX-WS requires endpoint interfaces
and implementation classes to be annotated with @WebService, @SOAPBinding, etc.
annotations. This means that you cannot (easily) use plain Java interfaces and
implementation classes as JAX-WS endpoint artifacts; you need to annotate them
accordingly first. Check the JAX-WS documentation for details on those requirements.
|
|
Warning
|
As of Spring Framework 5.3, RMI support is deprecated and will not be replaced. |
By using Spring’s support for RMI, you can transparently expose your services through the RMI infrastructure. After having this set up, you basically have a configuration similar to remote EJBs, except for the fact that there is no standard support for security context propagation or remote transaction propagation. Spring does provide hooks for such additional invocation context when you use the RMI invoker, so you can, for example, plug in security frameworks or custom security credentials.
Using the RmiServiceExporter, we can expose the interface of our AccountService object
as RMI object. The interface can be accessed by using RmiProxyFactoryBean, or via
plain RMI in case of a traditional RMI service. The RmiServiceExporter explicitly
supports the exposing of any non-RMI services via RMI invokers.
We first have to set up our service in the Spring container. The following example shows how to do so:
<bean id="accountService" class="example.AccountServiceImpl">
<!-- any additional properties, maybe a DAO? -->
</bean>Next, we have to expose our service by using RmiServiceExporter.
The following example shows how to do so:
<bean class="org.springframework.remoting.rmi.RmiServiceExporter">
<!-- does not necessarily have to be the same name as the bean to be exported -->
<property name="serviceName" value="AccountService"/>
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
<!-- defaults to 1099 -->
<property name="registryPort" value="1199"/>
</bean>In the preceding example, we override the port for the RMI registry. Often, your application
server also maintains an RMI registry, and it is wise to not interfere with that one.
Furthermore, the service name is used to bind the service. So, in the preceding example, the
service is bound at 'rmi://HOST:1199/AccountService'. We use this URL later on to link in
the service at the client side.
|
Note
|
The servicePort property has been omitted (it defaults to 0). This means that an
anonymous port is used to communicate with the service.
|
Our client is a simple object that uses the AccountService to manage accounts,
as the following example shows:
public class SimpleObject {
private AccountService accountService;
public void setAccountService(AccountService accountService) {
this.accountService = accountService;
}
// additional methods using the accountService
}To link in the service on the client, we create a separate Spring container, to contain the following simple object and the service linking configuration bits:
<bean class="example.SimpleObject">
<property name="accountService" ref="accountService"/>
</bean>
<bean id="accountService" class="org.springframework.remoting.rmi.RmiProxyFactoryBean">
<property name="serviceUrl" value="rmi://HOST:1199/AccountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>That is all we need to do to support the remote account service on the client. Spring
transparently creates an invoker and remotely enables the account service through the
RmiServiceExporter. At the client, we link it in by using the RmiProxyFactoryBean.
|
Warning
|
As of Spring Framework 5.3, Hessian support is deprecated and will not be replaced. |
Hessian offers a binary HTTP-based remoting protocol. It is developed by Caucho, and you can find more information about Hessian itself at https://www.caucho.com/.
Hessian communicates through HTTP and does so by using a custom servlet. By using Spring’s
DispatcherServlet principles (see webmvc.adoc), we can wire up such a
servlet to expose your services. First, we have to create a new servlet in our application,
as shown in the following excerpt from web.xml:
<servlet>
<servlet-name>remoting</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>remoting</servlet-name>
<url-pattern>/remoting/*</url-pattern>
</servlet-mapping>If you are familiar with Spring’s DispatcherServlet principles, you probably
know that now you have to create a Spring container configuration resource named
remoting-servlet.xml (after the name of your servlet) in the WEB-INF directory.
The application context is used in the next section.
Alternatively, consider the use of Spring’s simpler HttpRequestHandlerServlet. Doing so
lets you embed the remote exporter definitions in your root application context (by
default, in WEB-INF/applicationContext.xml), with individual servlet definitions
pointing to specific exporter beans. In this case, each servlet name needs to match the bean name of
its target exporter.
In the newly created application context called remoting-servlet.xml, we create a
HessianServiceExporter to export our services, as the following example shows:
<bean id="accountService" class="example.AccountServiceImpl">
<!-- any additional properties, maybe a DAO? -->
</bean>
<bean name="/AccountService" class="org.springframework.remoting.caucho.HessianServiceExporter">
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>Now we are ready to link in the service at the client. No explicit handler mapping is
specified (to map request URLs onto services), so we use BeanNameUrlHandlerMapping
used. Hence, the service is exported at the URL indicated through its bean name
within the containing DispatcherServlet instance’s mapping (as defined earlier):
https://HOST:8080/remoting/AccountService.
Alternatively, you can create a HessianServiceExporter in your root application context (for example,
in WEB-INF/applicationContext.xml), as the following example shows:
<bean name="accountExporter" class="org.springframework.remoting.caucho.HessianServiceExporter">
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>In the latter case, you should define a corresponding servlet for this exporter in web.xml,
with the same end result: The exporter gets mapped to the request path at
/remoting/AccountService. Note that the servlet name needs to match the bean name of
the target exporter. The following example shows how to do so:
<servlet>
<servlet-name>accountExporter</servlet-name>
<servlet-class>org.springframework.web.context.support.HttpRequestHandlerServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>accountExporter</servlet-name>
<url-pattern>/remoting/AccountService</url-pattern>
</servlet-mapping>By using the HessianProxyFactoryBean, we can link in the service at the client. The same
principles apply as with the RMI example. We create a separate bean factory or
application context and mention the following beans where the SimpleObject is by using
the AccountService to manage accounts, as the following example shows:
<bean class="example.SimpleObject">
<property name="accountService" ref="accountService"/>
</bean>
<bean id="accountService" class="org.springframework.remoting.caucho.HessianProxyFactoryBean">
<property name="serviceUrl" value="https://remotehost:8080/remoting/AccountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>One of the advantages of Hessian is that we can easily apply HTTP basic authentication,
because both protocols are HTTP-based. Your normal HTTP server security mechanism can
be applied through using the web.xml security features, for example. Usually,
you need not use per-user security credentials here. Rather, you can use shared credentials that you define
at the HessianProxyFactoryBean level (similar to a JDBC DataSource), as the following example shows:
<bean class="org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping">
<property name="interceptors" ref="authorizationInterceptor"/>
</bean>
<bean id="authorizationInterceptor"
class="org.springframework.web.servlet.handler.UserRoleAuthorizationInterceptor">
<property name="authorizedRoles" value="administrator,operator"/>
</bean>In the preceding example, we explicitly mention the BeanNameUrlHandlerMapping and set
an interceptor, to let only administrators and operators call the beans mentioned in
this application context.
|
Note
|
The preceding example does not show a flexible kind of security infrastructure. For more options as far as security is concerned, have a look at the Spring Security project at https://projects.spring.io/spring-security/. |
|
Warning
|
As of Spring Framework 5.3, HTTP Invoker support is deprecated and will not be replaced. |
As opposed to Hessian, Spring HTTP invokers are both lightweight protocols that use their own slim serialization mechanisms and use the standard Java serialization mechanism to expose services through HTTP. This has a huge advantage if your arguments and return types are complex types that cannot be serialized by using the serialization mechanisms Hessian uses (see the next section for more considerations when you choose a remoting technology).
Under the hood, Spring uses either the standard facilities provided by the JDK or
Apache HttpComponents to perform HTTP calls. If you need more
advanced and easier-to-use functionality, use the latter. See
hc.apache.org/httpcomponents-client-ga/
for more information.
|
Caution
|
Be aware of vulnerabilities due to unsafe Java deserialization: Manipulated input streams can lead to unwanted code execution on the server during the deserialization step. As a consequence, do not expose HTTP invoker endpoints to untrusted clients. Rather, expose them only between your own services. In general, we strongly recommend using any other message format (such as JSON) instead. If you are concerned about security vulnerabilities due to Java serialization, consider the general-purpose serialization filter mechanism at the core JVM level, originally developed for JDK 9 but backported to JDK 8, 7 and 6 in the meantime. See https://blogs.oracle.com/java-platform-group/entry/incoming_filter_serialization_data_a and https://openjdk.java.net/jeps/290. |
Setting up the HTTP invoker infrastructure for a service object closely resembles the
way you would do the same by using Hessian. As Hessian support provides
HessianServiceExporter, Spring’s HttpInvoker support provides
org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter.
To expose the AccountService (mentioned earlier) within a Spring Web MVC
DispatcherServlet, the following configuration needs to be in place in the
dispatcher’s application context, as the following example shows:
<bean name="/AccountService" class="org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter">
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>Such an exporter definition is exposed through the DispatcherServlet instance’s standard
mapping facilities, as explained in the section on Hessian.
Alternatively, you can create an HttpInvokerServiceExporter in your root application context
(for example, in 'WEB-INF/applicationContext.xml'), as the following example shows:
<bean name="accountExporter" class="org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter">
<property name="service" ref="accountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>In addition, you can define a corresponding servlet for this exporter in web.xml, with the
servlet name matching the bean name of the target exporter, as the following example shows:
<servlet>
<servlet-name>accountExporter</servlet-name>
<servlet-class>org.springframework.web.context.support.HttpRequestHandlerServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>accountExporter</servlet-name>
<url-pattern>/remoting/AccountService</url-pattern>
</servlet-mapping>Again, linking in the service from the client much resembles the way you would do it when you use Hessian. By using a proxy, Spring can translate your calls to HTTP POST requests to the URL that points to the exported service. The following example shows how to configure this arrangement:
<bean id="httpInvokerProxy" class="org.springframework.remoting.httpinvoker.HttpInvokerProxyFactoryBean">
<property name="serviceUrl" value="https://remotehost:8080/remoting/AccountService"/>
<property name="serviceInterface" value="example.AccountService"/>
</bean>As mentioned earlier, you can choose what HTTP client you want to use. By default, the
HttpInvokerProxy uses the JDK’s HTTP functionality, but you can also use the Apache
HttpComponents client by setting the httpInvokerRequestExecutor property.
The following example shows how to do so:
<property name="httpInvokerRequestExecutor">
<bean class="org.springframework.remoting.httpinvoker.HttpComponentsHttpInvokerRequestExecutor"/>
</property>|
Warning
|
As of Spring Framework 5.3, JMS remoting support is deprecated and will not be replaced. |
You can also expose services transparently by using JMS as the underlying communication
protocol. The JMS remoting support in the Spring Framework is pretty basic. It sends
and receives on the same thread and in the same non-transactional Session.
As a result, throughput is implementation-dependent. Note that these single-threaded
and non-transactional constraints apply only to Spring’s JMS remoting support.
See JMS (Java Message Service) for information on Spring’s rich support for JMS-based messaging.
The following interface is used on both the server and the client sides:
package com.foo;
public interface CheckingAccountService {
public void cancelAccount(Long accountId);
}The following simple implementation of the preceding interface is used on the server-side:
package com.foo;
public class SimpleCheckingAccountService implements CheckingAccountService {
public void cancelAccount(Long accountId) {
System.out.println("Cancelling account [" + accountId + "]");
}
}The following configuration file contains the JMS-infrastructure beans that are shared on both the client and the server:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="connectionFactory" class="org.apache.activemq.ActiveMQConnectionFactory">
<property name="brokerURL" value="tcp://ep-t43:61616"/>
</bean>
<bean id="queue" class="org.apache.activemq.command.ActiveMQQueue">
<constructor-arg value="mmm"/>
</bean>
</beans>On the server, you need to expose the service object that uses the
JmsInvokerServiceExporter, as the following example shows:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="checkingAccountService"
class="org.springframework.jms.remoting.JmsInvokerServiceExporter">
<property name="serviceInterface" value="com.foo.CheckingAccountService"/>
<property name="service">
<bean class="com.foo.SimpleCheckingAccountService"/>
</property>
</bean>
<bean class="org.springframework.jms.listener.SimpleMessageListenerContainer">
<property name="connectionFactory" ref="connectionFactory"/>
<property name="destination" ref="queue"/>
<property name="concurrentConsumers" value="3"/>
<property name="messageListener" ref="checkingAccountService"/>
</bean>
</beans>package com.foo;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Server {
public static void main(String[] args) throws Exception {
new ClassPathXmlApplicationContext("com/foo/server.xml", "com/foo/jms.xml");
}
}The client merely needs to create a client-side proxy that implements the agreed-upon
interface (CheckingAccountService).
The following example defines beans that you can inject into other client-side objects (and the proxy takes care of forwarding the call to the server-side object via JMS):
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="checkingAccountService"
class="org.springframework.jms.remoting.JmsInvokerProxyFactoryBean">
<property name="serviceInterface" value="com.foo.CheckingAccountService"/>
<property name="connectionFactory" ref="connectionFactory"/>
<property name="queue" ref="queue"/>
</bean>
</beans>package com.foo;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Client {
public static void main(String[] args) throws Exception {
ApplicationContext ctx = new ClassPathXmlApplicationContext("com/foo/client.xml", "com/foo/jms.xml");
CheckingAccountService service = (CheckingAccountService) ctx.getBean("checkingAccountService");
service.cancelAccount(new Long(10));
}
}As a lightweight container, Spring is often considered an EJB replacement. We do believe that for many, if not most, applications and use cases, Spring, as a container, combined with its rich supporting functionality in the area of transactions, ORM and JDBC access, is a better choice than implementing equivalent functionality through an EJB container and EJBs.
However, it is important to note that using Spring does not prevent you from using EJBs. In fact, Spring makes it much easier to access EJBs and implement EJBs and functionality within them. Additionally, using Spring to access services provided by EJBs allows the implementation of those services to later transparently be switched between local EJB, remote EJB, or POJO (plain old Java object) variants, without the client code having to be changed.
In this chapter, we look at how Spring can help you access and implement EJBs. Spring provides particular value when accessing stateless session beans (SLSBs), so we begin by discussing this topic.
This section covers how to access EJBs.
To invoke a method on a local or remote stateless session bean, client code must
normally perform a JNDI lookup to obtain the (local or remote) EJB Home object and then use
a create method call on that object to obtain the actual (local or remote) EJB object.
One or more methods are then invoked on the EJB.
To avoid repeated low-level code, many EJB applications use the Service Locator and Business Delegate patterns. These are better than spraying JNDI lookups throughout client code, but their usual implementations have significant disadvantages:
-
Typically, code that uses EJBs depends on Service Locator or Business Delegate singletons, making it hard to test.
-
In the case of the Service Locator pattern used without a Business Delegate, application code still ends up having to invoke the
create()method on an EJB home and deal with the resulting exceptions. Thus, it remains tied to the EJB API and the complexity of the EJB programming model. -
Implementing the Business Delegate pattern typically results in significant code duplication, where we have to write numerous methods that call the same method on the EJB.
The Spring approach is to allow the creation and use of proxy objects (normally configured inside a Spring container), which act as codeless business delegates. You need not write another Service Locator, another JNDI lookup, or duplicate methods in a hand-coded Business Delegate unless you actually add real value in such code.
Assume that we have a web controller that needs to use a local EJB. We follow best
practice and use the EJB Business Methods Interface pattern, so that the EJB’s local
interface extends a non-EJB-specific business methods interface. We call this
business methods interface MyComponent. The following example shows such an interface:
public interface MyComponent {
...
}One of the main reasons to use the Business Methods Interface pattern is to ensure that
synchronization between method signatures in local interface and bean implementation
class is automatic. Another reason is that it later makes it much easier for us to
switch to a POJO (plain old Java object) implementation of the service if it makes sense
to do so. We also need to implement the local home interface and provide an
implementation class that implements SessionBean and the MyComponent business
methods interface. Now, the only Java coding we need to do to hook up our web tier
controller to the EJB implementation is to expose a setter method of type MyComponent
on the controller. This saves the reference as an instance variable in the
controller. The following example shows how to do so:
private MyComponent myComponent;
public void setMyComponent(MyComponent myComponent) {
this.myComponent = myComponent;
}We can subsequently use this instance variable in any business method in the controller.
Now, assuming we obtain our controller object out of a Spring container, we can
(in the same context) configure a LocalStatelessSessionProxyFactoryBean instance,
which is the EJB proxy object. We configure the proxy and set the
myComponent property of the controller with the following configuration entry:
<bean id="myComponent"
class="org.springframework.ejb.access.LocalStatelessSessionProxyFactoryBean">
<property name="jndiName" value="ejb/myBean"/>
<property name="businessInterface" value="com.mycom.MyComponent"/>
</bean>
<bean id="myController" class="com.mycom.myController">
<property name="myComponent" ref="myComponent"/>
</bean>A lot of work happens behind the scenes, courtesy of the Spring AOP framework,
although you are not forced to work with AOP concepts to enjoy the results. The
myComponent bean definition creates a proxy for the EJB, which implements the business
method interface. The EJB local home is cached on startup, so there is only a single JNDI
lookup. Each time the EJB is invoked, the proxy invokes the classname method on the
local EJB and invokes the corresponding business method on the EJB.
The myController bean definition sets the myComponent property of the controller
class to the EJB proxy.
Alternatively (and preferably in case of many such proxy definitions), consider using
the <jee:local-slsb> configuration element in Spring’s “jee” namespace.
The following example shows how to do so:
<jee:local-slsb id="myComponent" jndi-name="ejb/myBean"
business-interface="com.mycom.MyComponent"/>
<bean id="myController" class="com.mycom.myController">
<property name="myComponent" ref="myComponent"/>
</bean>This EJB access mechanism delivers huge simplification of application code. The web tier
code (or other EJB client code) has no dependence on the use of EJB. To
replace this EJB reference with a POJO or a mock object or other test stub, we could
change the myComponent bean definition without changing a line of Java code.
Additionally, we have not had to write a single line of JNDI lookup or other EJB plumbing
code as part of our application.
Benchmarks and experience in real applications indicate that the performance overhead of this approach (which involves reflective invocation of the target EJB) is minimal and is undetectable in typical use. Remember that we do not want to make fine-grained calls to EJBs anyway, as there is a cost associated with the EJB infrastructure in the application server.
There is one caveat with regards to the JNDI lookup. In a bean container, this class is
normally best used as a singleton (there is no reason to make it a prototype).
However, if that bean container pre-instantiates singletons (as do the various XML
ApplicationContext variants), you can have a problem if the bean container is loaded
before the EJB container loads the target EJB. That is because the JNDI lookup is
performed in the init() method of this class and then cached, but the EJB has not
been bound at the target location yet. The solution is to not pre-instantiate this
factory object but to let it be created on first use. In the XML containers, you can control this
by using the lazy-init attribute.
Although not of interest to the majority of Spring users, those doing
programmatic AOP work with EJBs may want to look at LocalSlsbInvokerInterceptor.
Accessing remote EJBs is essentially identical to accessing local EJBs, except that the
SimpleRemoteStatelessSessionProxyFactoryBean or <jee:remote-slsb> configuration
element is used. Of course, with or without Spring, remote invocation semantics apply: A
call to a method on an object in another VM in another computer does sometimes have to
be treated differently in terms of usage scenarios and failure handling.
Spring’s EJB client support adds one more advantage over the non-Spring approach.
Normally, it is problematic for EJB client code to be easily switched back and forth
between calling EJBs locally or remotely. This is because the remote interface methods
must declare that they throw RemoteException, and client code must deal with this,
while the local interface methods need not. Client code written for local EJBs that needs
to be moved to remote EJBs typically has to be modified to add handling for the remote
exceptions, and client code written for remote EJBs that needs to be moved to local
EJBs can either stay the same but do a lot of unnecessary handling of remote
exceptions or be modified to remove that code. With the Spring remote EJB
proxy, you can instead not declare any thrown RemoteException in your Business Method
Interface and implementing EJB code, have a remote interface that is identical (except
that it does throw RemoteException), and rely on the proxy to dynamically treat the two
interfaces as if they were the same. That is, client code does not have to deal with the
checked RemoteException class. Any actual RemoteException that is thrown during the
EJB invocation is re-thrown as the non-checked RemoteAccessException class, which
is a subclass of RuntimeException. You can then switch the target service at will
between a local EJB or remote EJB (or even plain Java object) implementation, without
the client code knowing or caring. Of course, this is optional: Nothing
stops you from declaring RemoteException in your business interface.
Accessing EJB 2.x Session Beans and EJB 3 Session Beans through Spring is largely
transparent. Spring’s EJB accessors, including the <jee:local-slsb> and
<jee:remote-slsb> facilities, transparently adapt to the actual component at runtime.
They handle a home interface if found (EJB 2.x style) or perform straight component
invocations if no home interface is available (EJB 3 style).
Note: For EJB 3 Session Beans, you can effectively use a JndiObjectFactoryBean /
<jee:jndi-lookup> as well, since fully usable component references are exposed for
plain JNDI lookups there. Defining explicit <jee:local-slsb> or <jee:remote-slsb>
lookups provides consistent and more explicit EJB access configuration.
Spring provides a JMS integration framework that simplifies the use of the JMS API in much the same way as Spring’s integration does for the JDBC API.
JMS can be roughly divided into two areas of functionality, namely the production and
consumption of messages. The JmsTemplate class is used for message production and
synchronous message reception. For asynchronous reception similar to Jakarta EE’s
message-driven bean style, Spring provides a number of message-listener containers that
you can use to create Message-Driven POJOs (MDPs). Spring also provides a declarative way
to create message listeners.
The org.springframework.jms.core package provides the core functionality for using
JMS. It contains JMS template classes that simplify the use of the JMS by handling the
creation and release of resources, much like the JdbcTemplate does for JDBC. The
design principle common to Spring template classes is to provide helper methods to
perform common operations and, for more sophisticated usage, delegate the essence of the
processing task to user-implemented callback interfaces. The JMS template follows the
same design. The classes offer various convenience methods for sending messages,
consuming messages synchronously, and exposing the JMS session and message producer to
the user.
The org.springframework.jms.support package provides JMSException translation
functionality. The translation converts the checked JMSException hierarchy to a
mirrored hierarchy of unchecked exceptions. If any provider-specific subclasses
of the checked jakarta.jms.JMSException exist, this exception is wrapped in the
unchecked UncategorizedJmsException.
The org.springframework.jms.support.converter package provides a MessageConverter
abstraction to convert between Java objects and JMS messages.
The org.springframework.jms.support.destination package provides various strategies
for managing JMS destinations, such as providing a service locator for destinations
stored in JNDI.
The org.springframework.jms.annotation package provides the necessary infrastructure
to support annotation-driven listener endpoints by using @JmsListener.
The org.springframework.jms.config package provides the parser implementation for the
jms namespace as well as the java config support to configure listener containers and
create listener endpoints.
Finally, the org.springframework.jms.connection package provides an implementation of
the ConnectionFactory suitable for use in standalone applications. It also contains an
implementation of Spring’s PlatformTransactionManager for JMS (the cunningly named
JmsTransactionManager). This allows for seamless integration of JMS as a transactional
resource into Spring’s transaction management mechanisms.
|
Note
|
As of Spring Framework 5, Spring’s JMS package fully supports JMS 2.0 and requires the JMS 2.0 API to be present at runtime. We recommend the use of a JMS 2.0 compatible provider. If you happen to use an older message broker in your system, you may try upgrading to a JMS 2.0 compatible driver for your existing broker generation. Alternatively, you may also try to run against a JMS 1.1 based driver, simply putting the JMS 2.0 API jar on the classpath but only using JMS 1.1 compatible API against your driver. Spring’s JMS support adheres to JMS 1.1 conventions by default, so with corresponding configuration it does support such a scenario. However, please consider this for transition scenarios only. |
This section describes how to use Spring’s JMS components.
The JmsTemplate class is the central class in the JMS core package. It simplifies the
use of JMS, since it handles the creation and release of resources when sending or
synchronously receiving messages.
Code that uses the JmsTemplate needs only to implement callback interfaces that give them
a clearly defined high-level contract. The MessageCreator callback interface creates a
message when given a Session provided by the calling code in JmsTemplate. To
allow for more complex usage of the JMS API, SessionCallback provides the
JMS session, and ProducerCallback exposes a Session and
MessageProducer pair.
The JMS API exposes two types of send methods, one that takes delivery mode, priority,
and time-to-live as Quality of Service (QOS) parameters and one that takes no QOS
parameters and uses default values. Since JmsTemplate has many send methods,
setting the QOS parameters have been exposed as bean properties to
avoid duplication in the number of send methods. Similarly, the timeout value for
synchronous receive calls is set by using the setReceiveTimeout property.
Some JMS providers allow the setting of default QOS values administratively through the
configuration of the ConnectionFactory. This has the effect that a call to a
MessageProducer instance’s send method (send(Destination destination, Message message))
uses different QOS default values than those specified in the JMS specification. In order
to provide consistent management of QOS values, the JmsTemplate must, therefore, be
specifically enabled to use its own QOS values by setting the boolean property
isExplicitQosEnabled to true.
For convenience, JmsTemplate also exposes a basic request-reply operation that allows
for sending a message and waiting for a reply on a temporary queue that is created as part of
the operation.
|
Important
|
Instances of the JmsTemplate class are thread-safe, once configured. This is
important, because it means that you can configure a single instance of a JmsTemplate
and then safely inject this shared reference into multiple collaborators. To be
clear, the JmsTemplate is stateful, in that it maintains a reference to a
ConnectionFactory, but this state is not conversational state.
|
As of Spring Framework 4.1, JmsMessagingTemplate is built on top of JmsTemplate
and provides an integration with the messaging abstraction — that is,
org.springframework.messaging.Message. This lets you create the message to
send in a generic manner.
The JmsTemplate requires a reference to a ConnectionFactory. The ConnectionFactory
is part of the JMS specification and serves as the entry point for working with JMS. It
is used by the client application as a factory to create connections with the JMS
provider and encapsulates various configuration parameters, many of which are
vendor-specific, such as SSL configuration options.
When using JMS inside an EJB, the vendor provides implementations of the JMS interfaces
so that they can participate in declarative transaction management and perform pooling
of connections and sessions. In order to use this implementation, Jakarta EE containers
typically require that you declare a JMS connection factory as a resource-ref inside
the EJB or servlet deployment descriptors. To ensure the use of these features with the
JmsTemplate inside an EJB, the client application should ensure that it references the
managed implementation of the ConnectionFactory.
The standard API involves creating many intermediate objects. To send a message, the following 'API' walk is performed:
ConnectionFactory->Connection->Session->MessageProducer->send
Between the ConnectionFactory and the Send operation, three intermediate
objects are created and destroyed. To optimize the resource usage and increase
performance, Spring provides two implementations of ConnectionFactory.
Spring provides an implementation of the ConnectionFactory interface,
SingleConnectionFactory, that returns the same Connection on all
createConnection() calls and ignores calls to close(). This is useful for testing and
standalone environments so that the same connection can be used for multiple
JmsTemplate calls that may span any number of transactions. SingleConnectionFactory
takes a reference to a standard ConnectionFactory that would typically come from JNDI.
The CachingConnectionFactory extends the functionality of SingleConnectionFactory
and adds the caching of Session, MessageProducer, and MessageConsumer instances. The initial
cache size is set to 1. You can use the sessionCacheSize property to increase the number of
cached sessions. Note that the number of actual cached sessions is more than that
number, as sessions are cached based on their acknowledgment mode, so there can be up to
four cached session instances (one for each
acknowledgment mode) when sessionCacheSize is set to one. MessageProducer and MessageConsumer instances are cached within their
owning session and also take into account the unique properties of the producers and
consumers when caching. MessageProducers are cached based on their destination.
MessageConsumers are cached based on a key composed of the destination, selector,
noLocal delivery flag, and the durable subscription name (if creating durable consumers).
Destinations, as ConnectionFactory instances, are JMS administered objects that you can store
and retrieve in JNDI. When configuring a Spring application context, you can use the
JNDI JndiObjectFactoryBean factory class or <jee:jndi-lookup> to perform dependency
injection on your object’s references to JMS destinations. However, this strategy
is often cumbersome if there are a large number of destinations in the application or if there
are advanced destination management features unique to the JMS provider. Examples of
such advanced destination management include the creation of dynamic destinations or
support for a hierarchical namespace of destinations. The JmsTemplate delegates the
resolution of a destination name to a JMS destination object that implements the
DestinationResolver interface. DynamicDestinationResolver is the default
implementation used by JmsTemplate and accommodates resolving dynamic destinations. A
JndiDestinationResolver is also provided to act as a service locator for
destinations contained in JNDI and optionally falls back to the behavior contained in
DynamicDestinationResolver.
Quite often, the destinations used in a JMS application are only known at runtime and,
therefore, cannot be administratively created when the application is deployed. This is
often because there is shared application logic between interacting system components
that create destinations at runtime according to a well-known naming convention. Even
though the creation of dynamic destinations is not part of the JMS specification, most
vendors have provided this functionality. Dynamic destinations are created with a user-defined name,
which differentiates them from temporary destinations, and are often
not registered in JNDI. The API used to create dynamic destinations varies from provider
to provider since the properties associated with the destination are vendor-specific.
However, a simple implementation choice that is sometimes made by vendors is to
disregard the warnings in the JMS specification and to use the method TopicSession
createTopic(String topicName) or the QueueSession createQueue(String
queueName) method to create a new destination with default destination properties. Depending
on the vendor implementation, DynamicDestinationResolver can then also create a
physical destination instead of only resolving one.
The boolean property pubSubDomain is used to configure the JmsTemplate with
knowledge of what JMS domain is being used. By default, the value of this property is
false, indicating that the point-to-point domain, Queues, is to be used. This property
(used by JmsTemplate) determines the behavior of dynamic destination resolution through
implementations of the DestinationResolver interface.
You can also configure the JmsTemplate with a default destination through the
property defaultDestination. The default destination is with send and receive
operations that do not refer to a specific destination.
One of the most common uses of JMS messages in the EJB world is to drive message-driven
beans (MDBs). Spring offers a solution to create message-driven POJOs (MDPs) in a way
that does not tie a user to an EJB container. (See Asynchronous reception: Message-Driven POJOs for detailed
coverage of Spring’s MDP support.) Since Spring Framework 4.1, endpoint methods can be
annotated with @JmsListener — see Annotation-driven Listener Endpoints for more details.
A message listener container is used to receive messages from a JMS message queue and
drive the MessageListener that is injected into it. The listener container is
responsible for all threading of message reception and dispatches into the listener for
processing. A message listener container is the intermediary between an MDP and a
messaging provider and takes care of registering to receive messages, participating in
transactions, resource acquisition and release, exception conversion, and so on. This
lets you write the (possibly complex) business logic
associated with receiving a message (and possibly respond to it), and delegates
boilerplate JMS infrastructure concerns to the framework.
There are two standard JMS message listener containers packaged with Spring, each with its specialized feature set.
This message listener container is the simpler of the two standard flavors. It creates
a fixed number of JMS sessions and consumers at startup, registers the listener by using
the standard JMS MessageConsumer.setMessageListener() method, and leaves it up the JMS
provider to perform listener callbacks. This variant does not allow for dynamic adaption
to runtime demands or for participation in externally managed transactions.
Compatibility-wise, it stays very close to the spirit of the standalone JMS
specification, but is generally not compatible with Jakarta EE’s JMS restrictions.
|
Note
|
While SimpleMessageListenerContainer does not allow for participation in externally
managed transactions, it does support native JMS transactions. To enable this feature,
you can switch the sessionTransacted flag to true or, in the XML namespace, set the
acknowledge attribute to transacted. Exceptions thrown from your listener then lead
to a rollback, with the message getting redelivered. Alternatively, consider using
CLIENT_ACKNOWLEDGE mode, which provides redelivery in case of an exception as well but
does not use transacted Session instances and, therefore, does not include any other
Session operations (such as sending response messages) in the transaction protocol.
|
|
Important
|
The default AUTO_ACKNOWLEDGE mode does not provide proper reliability guarantees.
Messages can get lost when listener execution fails (since the provider automatically
acknowledges each message after listener invocation, with no exceptions to be propagated to
the provider) or when the listener container shuts down (you can configure this by setting
the acceptMessagesWhileStopping flag). Make sure to use transacted sessions in case of
reliability needs (for example, for reliable queue handling and durable topic subscriptions).
|
This message listener container is used in most cases. In contrast to
SimpleMessageListenerContainer, this container variant allows for dynamic adaptation
to runtime demands and is able to participate in externally managed transactions.
Each received message is registered with an XA transaction when configured with a
JtaTransactionManager. As a result, processing may take advantage of XA transaction
semantics. This listener container strikes a good balance between low requirements on
the JMS provider, advanced functionality (such as participation in externally managed
transactions), and compatibility with Jakarta EE environments.
You can customize the cache level of the container. Note that, when no caching is enabled, a new connection and a new session is created for each message reception. Combining this with a non-durable subscription with high loads may lead to message loss. Make sure to use a proper cache level in such a case.
This container also has recoverable capabilities when the broker goes down. By default,
a simple BackOff implementation retries every five seconds. You can specify
a custom BackOff implementation for more fine-grained recovery options. See
{api-spring-framework}/util/backoff/ExponentialBackOff.html[ExponentialBackOff] for an example.
|
Note
|
Like its sibling (SimpleMessageListenerContainer),
DefaultMessageListenerContainer supports native JMS transactions and allows for
customizing the acknowledgment mode. If feasible for your scenario, This is strongly
recommended over externally managed transactions — that is, if you can live with
occasional duplicate messages in case of the JVM dying. Custom duplicate message
detection steps in your business logic can cover such situations — for example,
in the form of a business entity existence check or a protocol table check.
Any such arrangements are significantly more efficient than the alternative:
wrapping your entire processing with an XA transaction (through configuring your
DefaultMessageListenerContainer with an JtaTransactionManager) to cover the
reception of the JMS message as well as the execution of the business logic in your
message listener (including database operations, etc.).
|
|
Important
|
The default AUTO_ACKNOWLEDGE mode does not provide proper reliability guarantees.
Messages can get lost when listener execution fails (since the provider automatically
acknowledges each message after listener invocation, with no exceptions to be propagated to
the provider) or when the listener container shuts down (you can configure this by setting
the acceptMessagesWhileStopping flag). Make sure to use transacted sessions in case of
reliability needs (for example, for reliable queue handling and durable topic subscriptions).
|
Spring provides a JmsTransactionManager that manages transactions for a single JMS
ConnectionFactory. This lets JMS applications leverage the managed-transaction
features of Spring, as described in
Transaction Management section of the Data Access chapter.
The JmsTransactionManager performs local resource transactions, binding a JMS
Connection/Session pair from the specified ConnectionFactory to the thread.
JmsTemplate automatically detects such transactional resources and operates
on them accordingly.
In a Jakarta EE environment, the ConnectionFactory pools Connection and Session instances,
so those resources are efficiently reused across transactions. In a standalone environment,
using Spring’s SingleConnectionFactory result in a shared JMS Connection, with
each transaction having its own independent Session. Alternatively, consider the use
of a provider-specific pooling adapter, such as ActiveMQ’s PooledConnectionFactory
class.
You can also use JmsTemplate with the JtaTransactionManager and an XA-capable JMS
ConnectionFactory to perform distributed transactions. Note that this requires the
use of a JTA transaction manager as well as a properly XA-configured ConnectionFactory.
(Check your Jakarta EE server’s or JMS provider’s documentation.)
Reusing code across a managed and unmanaged transactional environment can be confusing
when using the JMS API to create a Session from a Connection. This is because the
JMS API has only one factory method to create a Session, and it requires values for the
transaction and acknowledgment modes. In a managed environment, setting these values is
the responsibility of the environment’s transactional infrastructure, so these values
are ignored by the vendor’s wrapper to the JMS Connection. When you use the JmsTemplate
in an unmanaged environment, you can specify these values through the use of the
properties sessionTransacted and sessionAcknowledgeMode. When you use a
PlatformTransactionManager with JmsTemplate, the template is always given a
transactional JMS Session.
The JmsTemplate contains many convenience methods to send a message. Send
methods specify the destination by using a jakarta.jms.Destination object, and others
specify the destination by using a String in a JNDI lookup. The send method
that takes no destination argument uses the default destination.
The following example uses the MessageCreator callback to create a text message from the
supplied Session object:
import jakarta.jms.ConnectionFactory;
import jakarta.jms.JMSException;
import jakarta.jms.Message;
import jakarta.jms.Queue;
import jakarta.jms.Session;
import org.springframework.jms.core.MessageCreator;
import org.springframework.jms.core.JmsTemplate;
public class JmsQueueSender {
private JmsTemplate jmsTemplate;
private Queue queue;
public void setConnectionFactory(ConnectionFactory cf) {
this.jmsTemplate = new JmsTemplate(cf);
}
public void setQueue(Queue queue) {
this.queue = queue;
}
public void simpleSend() {
this.jmsTemplate.send(this.queue, new MessageCreator() {
public Message createMessage(Session session) throws JMSException {
return session.createTextMessage("hello queue world");
}
});
}
}In the preceding example, the JmsTemplate is constructed by passing a reference to a
ConnectionFactory. As an alternative, a zero-argument constructor and
connectionFactory is provided and can be used for constructing the instance in
JavaBean style (using a BeanFactory or plain Java code). Alternatively, consider
deriving from Spring’s JmsGatewaySupport convenience base class, which provides
pre-built bean properties for JMS configuration.
The send(String destinationName, MessageCreator creator) method lets you send a
message by using the string name of the destination. If these names are registered in JNDI,
you should set the destinationResolver property of the template to an instance of
JndiDestinationResolver.
If you created the JmsTemplate and specified a default destination, the
send(MessageCreator c) sends a message to that destination.
To facilitate the sending of domain model objects, the JmsTemplate has
various send methods that take a Java object as an argument for a message’s data
content. The overloaded methods convertAndSend() and receiveAndConvert() methods in
JmsTemplate delegate the conversion process to an instance of the MessageConverter
interface. This interface defines a simple contract to convert between Java objects and
JMS messages. The default implementation (SimpleMessageConverter) supports conversion
between String and TextMessage, byte[] and BytesMessage, and java.util.Map
and MapMessage. By using the converter, you and your application code can focus on the
business object that is being sent or received through JMS and not be concerned with the
details of how it is represented as a JMS message.
The sandbox currently includes a MapMessageConverter, which uses reflection to convert
between a JavaBean and a MapMessage. Other popular implementation choices you might
implement yourself are converters that use an existing XML marshalling package (such as
JAXB or XStream) to create a TextMessage that represents the object.
To accommodate the setting of a message’s properties, headers, and body that can not be
generically encapsulated inside a converter class, the MessagePostProcessor interface
gives you access to the message after it has been converted but before it is sent. The
following example shows how to modify a message header and a property after a
java.util.Map is converted to a message:
public void sendWithConversion() {
Map map = new HashMap();
map.put("Name", "Mark");
map.put("Age", new Integer(47));
jmsTemplate.convertAndSend("testQueue", map, new MessagePostProcessor() {
public Message postProcessMessage(Message message) throws JMSException {
message.setIntProperty("AccountID", 1234);
message.setJMSCorrelationID("123-00001");
return message;
}
});
}This results in a message of the following form:
MapMessage={
Header={
... standard headers ...
CorrelationID={123-00001}
}
Properties={
AccountID={Integer:1234}
}
Fields={
Name={String:Mark}
Age={Integer:47}
}
}
While the send operations cover many common usage scenarios, you might sometimes
want to perform multiple operations on a JMS Session or MessageProducer. The
SessionCallback and ProducerCallback expose the JMS Session and Session /
MessageProducer pair, respectively. The execute() methods on JmsTemplate run
these callback methods.
This describes how to receive messages with JMS in Spring.
While JMS is typically associated with asynchronous processing, you can
consume messages synchronously. The overloaded receive(..) methods provide this
functionality. During a synchronous receive, the calling thread blocks until a message
becomes available. This can be a dangerous operation, since the calling thread can
potentially be blocked indefinitely. The receiveTimeout property specifies how long
the receiver should wait before giving up waiting for a message.
|
Note
|
Spring also supports annotated-listener endpoints through the use of the @JmsListener
annotation and provides an open infrastructure to register endpoints programmatically.
This is, by far, the most convenient way to setup an asynchronous receiver.
See Enable Listener Endpoint Annotations for more details.
|
In a fashion similar to a Message-Driven Bean (MDB) in the EJB world, the Message-Driven
POJO (MDP) acts as a receiver for JMS messages. The one restriction (but see
Using MessageListenerAdapter) on an MDP is that it must implement
the jakarta.jms.MessageListener interface. Note that, if your POJO receives messages
on multiple threads, it is important to ensure that your implementation is thread-safe.
The following example shows a simple implementation of an MDP:
import jakarta.jms.JMSException;
import jakarta.jms.Message;
import jakarta.jms.MessageListener;
import jakarta.jms.TextMessage;
public class ExampleListener implements MessageListener {
public void onMessage(Message message) {
if (message instanceof TextMessage) {
try {
System.out.println(((TextMessage) message).getText());
}
catch (JMSException ex) {
throw new RuntimeException(ex);
}
}
else {
throw new IllegalArgumentException("Message must be of type TextMessage");
}
}
}Once you have implemented your MessageListener, it is time to create a message listener
container.
The following example shows how to define and configure one of the message listener
containers that ships with Spring (in this case, DefaultMessageListenerContainer):
<!-- this is the Message Driven POJO (MDP) -->
<bean id="messageListener" class="jmsexample.ExampleListener"/>
<!-- and this is the message listener container -->
<bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer">
<property name="connectionFactory" ref="connectionFactory"/>
<property name="destination" ref="destination"/>
<property name="messageListener" ref="messageListener"/>
</bean>See the Spring javadoc of the various message listener containers (all of which implement {api-spring-framework}/jms/listener/MessageListenerContainer.html[MessageListenerContainer]) for a full description of the features supported by each implementation.
The SessionAwareMessageListener interface is a Spring-specific interface that provides
a similar contract to the JMS MessageListener interface but also gives the message-handling
method access to the JMS Session from which the Message was received.
The following listing shows the definition of the SessionAwareMessageListener interface:
package org.springframework.jms.listener;
public interface SessionAwareMessageListener {
void onMessage(Message message, Session session) throws JMSException;
}You can choose to have your MDPs implement this interface (in preference to the standard
JMS MessageListener interface) if you want your MDPs to be able to respond to any
received messages (by using the Session supplied in the onMessage(Message, Session)
method). All of the message listener container implementations that ship with Spring
have support for MDPs that implement either the MessageListener or
SessionAwareMessageListener interface. Classes that implement the
SessionAwareMessageListener come with the caveat that they are then tied to Spring
through the interface. The choice of whether or not to use it is left entirely up to you
as an application developer or architect.
Note that the onMessage(..) method of the SessionAwareMessageListener
interface throws JMSException. In contrast to the standard JMS MessageListener
interface, when using the SessionAwareMessageListener interface, it is the
responsibility of the client code to handle any thrown exceptions.
The MessageListenerAdapter class is the final component in Spring’s asynchronous
messaging support. In a nutshell, it lets you expose almost any class as an MDP
(though there are some constraints).
Consider the following interface definition:
public interface MessageDelegate {
void handleMessage(String message);
void handleMessage(Map message);
void handleMessage(byte[] message);
void handleMessage(Serializable message);
}Notice that, although the interface extends neither the MessageListener nor the
SessionAwareMessageListener interface, you can still use it as an MDP by using the
MessageListenerAdapter class. Notice also how the various message handling methods are
strongly typed according to the contents of the various Message types that they can
receive and handle.
Now consider the following implementation of the MessageDelegate interface:
public class DefaultMessageDelegate implements MessageDelegate {
// implementation elided for clarity...
}In particular, note how the preceding implementation of the MessageDelegate interface (the
DefaultMessageDelegate class) has no JMS dependencies at all. It truly is a
POJO that we can make into an MDP through the following configuration:
<!-- this is the Message Driven POJO (MDP) -->
<bean id="messageListener" class="org.springframework.jms.listener.adapter.MessageListenerAdapter">
<constructor-arg>
<bean class="jmsexample.DefaultMessageDelegate"/>
</constructor-arg>
</bean>
<!-- and this is the message listener container... -->
<bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer">
<property name="connectionFactory" ref="connectionFactory"/>
<property name="destination" ref="destination"/>
<property name="messageListener" ref="messageListener"/>
</bean>The next example shows another MDP that can handle only receiving JMS
TextMessage messages. Notice how the message handling method is actually called
receive (the name of the message handling method in a MessageListenerAdapter
defaults to handleMessage), but it is configurable (as you can see later in this section). Notice
also how the receive(..) method is strongly typed to receive and respond only to JMS
TextMessage messages.
The following listing shows the definition of the TextMessageDelegate interface:
public interface TextMessageDelegate {
void receive(TextMessage message);
}The following listing shows a class that implements the TextMessageDelegate interface:
public class DefaultTextMessageDelegate implements TextMessageDelegate {
// implementation elided for clarity...
}The configuration of the attendant MessageListenerAdapter would then be as follows:
<bean id="messageListener" class="org.springframework.jms.listener.adapter.MessageListenerAdapter">
<constructor-arg>
<bean class="jmsexample.DefaultTextMessageDelegate"/>
</constructor-arg>
<property name="defaultListenerMethod" value="receive"/>
<!-- we don't want automatic message context extraction -->
<property name="messageConverter">
<null/>
</property>
</bean>Note that, if the messageListener receives a JMS Message of a type
other than TextMessage, an IllegalStateException is thrown (and subsequently
swallowed). Another of the capabilities of the MessageListenerAdapter class is the
ability to automatically send back a response Message if a handler method returns a
non-void value. Consider the following interface and class:
public interface ResponsiveTextMessageDelegate {
// notice the return type...
String receive(TextMessage message);
}public class DefaultResponsiveTextMessageDelegate implements ResponsiveTextMessageDelegate {
// implementation elided for clarity...
}If you use the DefaultResponsiveTextMessageDelegate in conjunction with a
MessageListenerAdapter, any non-null value that is returned from the execution of
the 'receive(..)' method is (in the default configuration) converted into a
TextMessage. The resulting TextMessage is then sent to the Destination (if
one exists) defined in the JMS Reply-To property of the original Message or the
default Destination set on the MessageListenerAdapter (if one has been configured).
If no Destination is found, an InvalidDestinationException is thrown
(note that this exception is not swallowed and propagates up the
call stack).
Invoking a message listener within a transaction requires only reconfiguration of the listener container.
You can activate local resource transactions through the sessionTransacted flag
on the listener container definition. Each message listener invocation then operates
within an active JMS transaction, with message reception rolled back in case of listener
execution failure. Sending a response message (through SessionAwareMessageListener) is
part of the same local transaction, but any other resource operations (such as
database access) operate independently. This usually requires duplicate message
detection in the listener implementation, to cover the case where database processing
has committed but message processing failed to commit.
Consider the following bean definition:
<bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer">
<property name="connectionFactory" ref="connectionFactory"/>
<property name="destination" ref="destination"/>
<property name="messageListener" ref="messageListener"/>
<property name="sessionTransacted" value="true"/>
</bean>To participate in an externally managed transaction, you need to configure a
transaction manager and use a listener container that supports externally managed
transactions (typically, DefaultMessageListenerContainer).
To configure a message listener container for XA transaction participation, you want
to configure a JtaTransactionManager (which, by default, delegates to the Jakarta EE
server’s transaction subsystem). Note that the underlying JMS ConnectionFactory needs to
be XA-capable and properly registered with your JTA transaction coordinator. (Check your
Jakarta EE server’s configuration of JNDI resources.) This lets message reception as well
as (for example) database access be part of the same transaction (with unified commit
semantics, at the expense of XA transaction log overhead).
The following bean definition creates a transaction manager:
<bean id="transactionManager" class="org.springframework.transaction.jta.JtaTransactionManager"/>Then we need to add it to our earlier container configuration. The container takes care of the rest. The following example shows how to do so:
<bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer">
<property name="connectionFactory" ref="connectionFactory"/>
<property name="destination" ref="destination"/>
<property name="messageListener" ref="messageListener"/>
<property name="transactionManager" ref="transactionManager"/> (1)
</bean>-
Our transaction manager.
Beginning with version 2.5, Spring also provides support for a JCA-based
MessageListener container. The JmsMessageEndpointManager tries to
automatically determine the ActivationSpec class name from the provider’s
ResourceAdapter class name. Therefore, it is typically possible to provide
Spring’s generic JmsActivationSpecConfig, as the following example shows:
<bean class="org.springframework.jms.listener.endpoint.JmsMessageEndpointManager">
<property name="resourceAdapter" ref="resourceAdapter"/>
<property name="activationSpecConfig">
<bean class="org.springframework.jms.listener.endpoint.JmsActivationSpecConfig">
<property name="destinationName" value="myQueue"/>
</bean>
</property>
<property name="messageListener" ref="myMessageListener"/>
</bean>Alternatively, you can set up a JmsMessageEndpointManager with a given
ActivationSpec object. The ActivationSpec object may also come from a JNDI lookup
(using <jee:jndi-lookup>). The following example shows how to do so:
<bean class="org.springframework.jms.listener.endpoint.JmsMessageEndpointManager">
<property name="resourceAdapter" ref="resourceAdapter"/>
<property name="activationSpec">
<bean class="org.apache.activemq.ra.ActiveMQActivationSpec">
<property name="destination" value="myQueue"/>
<property name="destinationType" value="jakarta.jms.Queue"/>
</bean>
</property>
<property name="messageListener" ref="myMessageListener"/>
</bean>Using Spring’s ResourceAdapterFactoryBean, you can configure the target ResourceAdapter
locally, as the following example shows:
<bean id="resourceAdapter" class="org.springframework.jca.support.ResourceAdapterFactoryBean">
<property name="resourceAdapter">
<bean class="org.apache.activemq.ra.ActiveMQResourceAdapter">
<property name="serverUrl" value="tcp://localhost:61616"/>
</bean>
</property>
<property name="workManager">
<bean class="org.springframework.jca.work.SimpleTaskWorkManager"/>
</property>
</bean>The specified WorkManager can also point to an environment-specific thread pool — typically through a SimpleTaskWorkManager instance’s asyncTaskExecutor property. Consider
defining a shared thread pool for all your ResourceAdapter instances if you happen to
use multiple adapters.
In some environments (such as WebLogic 9 or above), you can instead obtain the entire ResourceAdapter object
from JNDI (by using <jee:jndi-lookup>). The Spring-based message
listeners can then interact with the server-hosted ResourceAdapter, which also use the
server’s built-in WorkManager.
See the javadoc for {api-spring-framework}/jms/listener/endpoint/JmsMessageEndpointManager.html[JmsMessageEndpointManager],
{api-spring-framework}/jms/listener/endpoint/JmsActivationSpecConfig.html[JmsActivationSpecConfig],
and {api-spring-framework}/jca/support/ResourceAdapterFactoryBean.html[ResourceAdapterFactoryBean]
for more details.
Spring also provides a generic JCA message endpoint manager that is not tied to JMS:
org.springframework.jca.endpoint.GenericMessageEndpointManager. This component allows
for using any message listener type (such as a JMS MessageListener) and any
provider-specific ActivationSpec object. See your JCA provider’s documentation to
find out about the actual capabilities of your connector, and see the
{api-spring-framework}/jca/endpoint/GenericMessageEndpointManager.html[GenericMessageEndpointManager]
javadoc for the Spring-specific configuration details.
|
Note
|
JCA-based message endpoint management is very analogous to EJB 2.1 Message-Driven Beans. It uses the same underlying resource provider contract. As with EJB 2.1 MDBs, you can use any message listener interface supported by your JCA provider in the Spring context as well. Spring nevertheless provides explicit “convenience” support for JMS, because JMS is the most common endpoint API used with the JCA endpoint management contract. |
The easiest way to receive a message asynchronously is to use the annotated listener endpoint infrastructure. In a nutshell, it lets you expose a method of a managed bean as a JMS listener endpoint. The following example shows how to use it:
@Component
public class MyService {
@JmsListener(destination = "myDestination")
public void processOrder(String data) { ... }
}The idea of the preceding example is that, whenever a message is available on the
jakarta.jms.Destination myDestination, the processOrder method is invoked
accordingly (in this case, with the content of the JMS message, similar to
what the MessageListenerAdapter
provides).
The annotated endpoint infrastructure creates a message listener container
behind the scenes for each annotated method, by using a JmsListenerContainerFactory.
Such a container is not registered against the application context but can be easily
located for management purposes by using the JmsListenerEndpointRegistry bean.
|
Tip
|
@JmsListener is a repeatable annotation on Java 8, so you can associate
several JMS destinations with the same method by adding additional @JmsListener
declarations to it.
|
To enable support for @JmsListener annotations, you can add @EnableJms to one of
your @Configuration classes, as the following example shows:
@Configuration
@EnableJms
public class AppConfig {
@Bean
public DefaultJmsListenerContainerFactory jmsListenerContainerFactory() {
DefaultJmsListenerContainerFactory factory = new DefaultJmsListenerContainerFactory();
factory.setConnectionFactory(connectionFactory());
factory.setDestinationResolver(destinationResolver());
factory.setSessionTransacted(true);
factory.setConcurrency("3-10");
return factory;
}
}By default, the infrastructure looks for a bean named jmsListenerContainerFactory
as the source for the factory to use to create message listener containers. In this
case (and ignoring the JMS infrastructure setup), you can invoke the processOrder
method with a core poll size of three threads and a maximum pool size of ten threads.
You can customize the listener container factory to use for each annotation or you can
configure an explicit default by implementing the JmsListenerConfigurer interface.
The default is required only if at least one endpoint is registered without a specific
container factory. See the javadoc of classes that implement
{api-spring-framework}/jms/annotation/JmsListenerConfigurer.html[JmsListenerConfigurer]
for details and examples.
If you prefer XML configuration, you can use the <jms:annotation-driven>
element, as the following example shows:
<jms:annotation-driven/>
<bean id="jmsListenerContainerFactory"
class="org.springframework.jms.config.DefaultJmsListenerContainerFactory">
<property name="connectionFactory" ref="connectionFactory"/>
<property name="destinationResolver" ref="destinationResolver"/>
<property name="sessionTransacted" value="true"/>
<property name="concurrency" value="3-10"/>
</bean>JmsListenerEndpoint provides a model of a JMS endpoint and is responsible for configuring
the container for that model. The infrastructure lets you programmatically configure endpoints
in addition to the ones that are detected by the JmsListener annotation.
The following example shows how to do so:
@Configuration
@EnableJms
public class AppConfig implements JmsListenerConfigurer {
@Override
public void configureJmsListeners(JmsListenerEndpointRegistrar registrar) {
SimpleJmsListenerEndpoint endpoint = new SimpleJmsListenerEndpoint();
endpoint.setId("myJmsEndpoint");
endpoint.setDestination("anotherQueue");
endpoint.setMessageListener(message -> {
// processing
});
registrar.registerEndpoint(endpoint);
}
}In the preceding example, we used SimpleJmsListenerEndpoint, which provides the actual
MessageListener to invoke. However, you could also build your own endpoint variant
to describe a custom invocation mechanism.
Note that you could skip the use of @JmsListener altogether
and programmatically register only your endpoints through JmsListenerConfigurer.
So far, we have been injecting a simple String in our endpoint, but it can actually
have a very flexible method signature. In the following example, we rewrite it to inject the Order with
a custom header:
@Component
public class MyService {
@JmsListener(destination = "myDestination")
public void processOrder(Order order, @Header("order_type") String orderType) {
...
}
}The main elements you can inject in JMS listener endpoints are as follows:
-
The raw
jakarta.jms.Messageor any of its subclasses (provided that it matches the incoming message type). -
The
jakarta.jms.Sessionfor optional access to the native JMS API (for example, for sending a custom reply). -
The
org.springframework.messaging.Messagethat represents the incoming JMS message. Note that this message holds both the custom and the standard headers (as defined byJmsHeaders). -
@Header-annotated method arguments to extract a specific header value, including standard JMS headers. -
A
@Headers-annotated argument that must also be assignable tojava.util.Mapfor getting access to all headers. -
A non-annotated element that is not one of the supported types (
MessageorSession) is considered to be the payload. You can make that explicit by annotating the parameter with@Payload. You can also turn on validation by adding an extra@Valid.
The ability to inject Spring’s Message abstraction is particularly useful to benefit
from all the information stored in the transport-specific message without relying on
transport-specific API. The following example shows how to do so:
@JmsListener(destination = "myDestination")
public void processOrder(Message<Order> order) { ... }Handling of method arguments is provided by DefaultMessageHandlerMethodFactory, which you can
further customize to support additional method arguments. You can customize the conversion and validation
support there as well.
For instance, if we want to make sure our Order is valid before processing it, we can
annotate the payload with @Valid and configure the necessary validator, as the following example shows:
@Configuration
@EnableJms
public class AppConfig implements JmsListenerConfigurer {
@Override
public void configureJmsListeners(JmsListenerEndpointRegistrar registrar) {
registrar.setMessageHandlerMethodFactory(myJmsHandlerMethodFactory());
}
@Bean
public DefaultMessageHandlerMethodFactory myHandlerMethodFactory() {
DefaultMessageHandlerMethodFactory factory = new DefaultMessageHandlerMethodFactory();
factory.setValidator(myValidator());
return factory;
}
}The existing support in MessageListenerAdapter
already lets your method have a non-void return type. When that is the case, the result of
the invocation is encapsulated in a jakarta.jms.Message, sent either in the destination specified
in the JMSReplyTo header of the original message or in the default destination configured on
the listener. You can now set that default destination by using the @SendTo annotation of the
messaging abstraction.
Assuming that our processOrder method should now return an OrderStatus, we can write it
to automatically send a response, as the following example shows:
@JmsListener(destination = "myDestination")
@SendTo("status")
public OrderStatus processOrder(Order order) {
// order processing
return status;
}|
Tip
|
If you have several @JmsListener-annotated methods, you can also place the @SendTo
annotation at the class level to share a default reply destination.
|
If you need to set additional headers in a transport-independent manner, you can return a
Message instead, with a method similar to the following:
@JmsListener(destination = "myDestination")
@SendTo("status")
public Message<OrderStatus> processOrder(Order order) {
// order processing
return MessageBuilder
.withPayload(status)
.setHeader("code", 1234)
.build();
}If you need to compute the response destination at runtime, you can encapsulate your response
in a JmsResponse instance that also provides the destination to use at runtime. We can rewrite the previous
example as follows:
@JmsListener(destination = "myDestination")
public JmsResponse<Message<OrderStatus>> processOrder(Order order) {
// order processing
Message<OrderStatus> response = MessageBuilder
.withPayload(status)
.setHeader("code", 1234)
.build();
return JmsResponse.forQueue(response, "status");
}Finally, if you need to specify some QoS values for the response such as the priority or
the time to live, you can configure the JmsListenerContainerFactory accordingly,
as the following example shows:
@Configuration
@EnableJms
public class AppConfig {
@Bean
public DefaultJmsListenerContainerFactory jmsListenerContainerFactory() {
DefaultJmsListenerContainerFactory factory = new DefaultJmsListenerContainerFactory();
factory.setConnectionFactory(connectionFactory());
QosSettings replyQosSettings = new QosSettings();
replyQosSettings.setPriority(2);
replyQosSettings.setTimeToLive(10000);
factory.setReplyQosSettings(replyQosSettings);
return factory;
}
}Spring provides an XML namespace for simplifying JMS configuration. To use the JMS namespace elements, you need to reference the JMS schema, as the following example shows:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jms="http://www.springframework.org/schema/jms" (1)
xsi:schemaLocation="
http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/jms https://www.springframework.org/schema/jms/spring-jms.xsd">
<!-- bean definitions here -->
</beans>-
Referencing the JMS schema.
The namespace consists of three top-level elements: <annotation-driven/>, <listener-container/>
and <jca-listener-container/>. <annotation-driven/> enables the use of annotation-driven listener endpoints. <listener-container/> and <jca-listener-container/>
define shared listener container configuration and can contain <listener/> child elements.
The following example shows a basic configuration for two listeners:
<jms:listener-container>
<jms:listener destination="queue.orders" ref="orderService" method="placeOrder"/>
<jms:listener destination="queue.confirmations" ref="confirmationLogger" method="log"/>
</jms:listener-container>The preceding example is equivalent to creating two distinct listener container bean
definitions and two distinct MessageListenerAdapter bean definitions, as shown
in Using MessageListenerAdapter. In addition to the attributes shown
in the preceding example, the listener element can contain several optional ones.
The following table describes all of the available attributes:
| Attribute | Description |
|---|---|
|
A bean name for the hosting listener container. If not specified, a bean name is automatically generated. |
|
The destination name for this listener, resolved through the |
|
The bean name of the handler object. |
|
The name of the handler method to invoke. If the |
|
The name of the default response destination to which to send response messages. This is
applied in case of a request message that does not carry a |
|
The name of the durable subscription, if any. |
|
An optional message selector for this listener. |
|
The number of concurrent sessions or consumers to start for this listener. This value can either be
a simple number indicating the maximum number (for example, |
The <listener-container/> element also accepts several optional attributes. This
allows for customization of the various strategies (for example, taskExecutor and
destinationResolver) as well as basic JMS settings and resource references. By using
these attributes, you can define highly-customized listener containers while
still benefiting from the convenience of the namespace.
You can automatically expose such settings as a JmsListenerContainerFactory by
specifying the id of the bean to expose through the factory-id attribute,
as the following example shows:
<jms:listener-container connection-factory="myConnectionFactory"
task-executor="myTaskExecutor"
destination-resolver="myDestinationResolver"
transaction-manager="myTransactionManager"
concurrency="10">
<jms:listener destination="queue.orders" ref="orderService" method="placeOrder"/>
<jms:listener destination="queue.confirmations" ref="confirmationLogger" method="log"/>
</jms:listener-container>The following table describes all available attributes. See the class-level javadoc
of the {api-spring-framework}/jms/listener/AbstractMessageListenerContainer.html[AbstractMessageListenerContainer]
and its concrete subclasses for more details on the individual properties. The javadoc
also provides a discussion of transaction choices and message redelivery scenarios.
| Attribute | Description |
|---|---|
|
The type of this listener container. The available options are |
|
A custom listener container implementation class as a fully qualified class name.
The default is Spring’s standard |
|
Exposes the settings defined by this element as a |
|
A reference to the JMS |
|
A reference to the Spring |
|
A reference to the |
|
A reference to the |
|
A reference to an |
|
The JMS destination type for this listener: |
|
The JMS destination type for responses: |
|
The JMS client ID for this listener container. You must specify it when you use durable subscriptions. |
|
The cache level for JMS resources: |
|
The native JMS acknowledge mode: |
|
A reference to an external |
|
The number of concurrent sessions or consumers to start for each listener. It can either be
a simple number indicating the maximum number (for example, |
|
The maximum number of messages to load into a single session. Note that raising this number might lead to starvation of concurrent consumers. |
|
The timeout (in milliseconds) to use for receive calls. The default is |
|
Specifies the |
|
Specifies the interval between recovery attempts, in milliseconds. It offers a convenient
way to create a |
|
The lifecycle phase within which this container should start and stop. The lower the
value, the earlier this container starts and the later it stops. The default is
|
Configuring a JCA-based listener container with the jms schema support is very similar,
as the following example shows:
<jms:jca-listener-container resource-adapter="myResourceAdapter"
destination-resolver="myDestinationResolver"
transaction-manager="myTransactionManager"
concurrency="10">
<jms:listener destination="queue.orders" ref="myMessageListener"/>
</jms:jca-listener-container>The following table describes the available configuration options for the JCA variant:
| Attribute | Description |
|---|---|
|
Exposes the settings defined by this element as a |
|
A reference to the JCA |
|
A reference to the |
|
A reference to the |
|
A reference to the |
|
The JMS destination type for this listener: |
|
The JMS destination type for responses: |
|
The JMS client ID for this listener container. It needs to be specified when using durable subscriptions. |
|
The native JMS acknowledge mode: |
|
A reference to a Spring |
|
The number of concurrent sessions or consumers to start for each listener. It can either be
a simple number indicating the maximum number (for example |
|
The maximum number of messages to load into a single session. Note that raising this number might lead to starvation of concurrent consumers. |
The JMX (Java Management Extensions) support in Spring provides features that let you easily and transparently integrate your Spring application into a JMX infrastructure.
This chapter is not an introduction to JMX. It does not try to explain why you might want to use JMX. If you are new to JMX, see Further Resources at the end of this chapter.
Specifically, Spring’s JMX support provides four core features:
-
The automatic registration of any Spring bean as a JMX MBean.
-
A flexible mechanism for controlling the management interface of your beans.
-
The declarative exposure of MBeans over remote, JSR-160 connectors.
-
The simple proxying of both local and remote MBean resources.
These features are designed to work without coupling your application components to either Spring or JMX interfaces and classes. Indeed, for the most part, your application classes need not be aware of either Spring or JMX in order to take advantage of the Spring JMX features.
The core class in Spring’s JMX framework is the MBeanExporter. This class is
responsible for taking your Spring beans and registering them with a JMX MBeanServer.
For example, consider the following class:
package org.springframework.jmx;
public class JmxTestBean implements IJmxTestBean {
private String name;
private int age;
private boolean isSuperman;
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
public int add(int x, int y) {
return x + y;
}
public void dontExposeMe() {
throw new RuntimeException();
}
}To expose the properties and methods of this bean as attributes and operations of an
MBean, you can configure an instance of the MBeanExporter class in your
configuration file and pass in the bean, as the following example shows:
<beans>
<!-- this bean must not be lazily initialized if the exporting is to happen -->
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter" lazy-init="false">
<property name="beans">
<map>
<entry key="bean:name=testBean1" value-ref="testBean"/>
</map>
</property>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>The pertinent bean definition from the preceding configuration snippet is the exporter
bean. The beans property tells the MBeanExporter exactly which of your beans must be
exported to the JMX MBeanServer. In the default configuration, the key of each entry
in the beans Map is used as the ObjectName for the bean referenced by the
corresponding entry value. You can change this behavior, as described in Controlling ObjectName Instances for Your Beans.
With this configuration, the testBean bean is exposed as an MBean under the
ObjectName bean:name=testBean1. By default, all public properties of the bean
are exposed as attributes and all public methods (except those inherited from the
Object class) are exposed as operations.
|
Note
|
MBeanExporter is a Lifecycle bean (see Startup and Shutdown Callbacks). By default, MBeans are exported as late as possible during
the application lifecycle. You can configure the phase at which
the export happens or disable automatic registration by setting the autoStartup flag.
|
The configuration shown in the preceding section assumes that the
application is running in an environment that has one (and only one) MBeanServer
already running. In this case, Spring tries to locate the running MBeanServer and
register your beans with that server (if any). This behavior is useful when your
application runs inside a container (such as Tomcat or IBM WebSphere) that has its
own MBeanServer.
However, this approach is of no use in a standalone environment or when running inside
a container that does not provide an MBeanServer. To address this, you can create an
MBeanServer instance declaratively by adding an instance of the
org.springframework.jmx.support.MBeanServerFactoryBean class to your configuration.
You can also ensure that a specific MBeanServer is used by setting the value of the
MBeanExporter instance’s server property to the MBeanServer value returned by an
MBeanServerFactoryBean, as the following example shows:
<beans>
<bean id="mbeanServer" class="org.springframework.jmx.support.MBeanServerFactoryBean"/>
<!--
this bean needs to be eagerly pre-instantiated in order for the exporting to occur;
this means that it must not be marked as lazily initialized
-->
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean1" value-ref="testBean"/>
</map>
</property>
<property name="server" ref="mbeanServer"/>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>In the preceding example, an instance of MBeanServer is created by the MBeanServerFactoryBean and is
supplied to the MBeanExporter through the server property. When you supply your own
MBeanServer instance, the MBeanExporter does not try to locate a running
MBeanServer and uses the supplied MBeanServer instance. For this to work
correctly, you must have a JMX implementation on your classpath.
If no server is specified, the MBeanExporter tries to automatically detect a running
MBeanServer. This works in most environments, where only one MBeanServer instance is
used. However, when multiple instances exist, the exporter might pick the wrong server.
In such cases, you should use the MBeanServer agentId to indicate which instance to
be used, as the following example shows:
<beans>
<bean id="mbeanServer" class="org.springframework.jmx.support.MBeanServerFactoryBean">
<!-- indicate to first look for a server -->
<property name="locateExistingServerIfPossible" value="true"/>
<!-- search for the MBeanServer instance with the given agentId -->
<property name="agentId" value="MBeanServer_instance_agentId>"/>
</bean>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="server" ref="mbeanServer"/>
...
</bean>
</beans>For platforms or cases where the existing MBeanServer has a dynamic (or unknown)
agentId that is retrieved through lookup methods, you should use
factory-method,
as the following example shows:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="server">
<!-- Custom MBeanServerLocator -->
<bean class="platform.package.MBeanServerLocator" factory-method="locateMBeanServer"/>
</property>
</bean>
<!-- other beans here -->
</beans>If you configure a bean with an MBeanExporter that is also configured for lazy
initialization, the MBeanExporter does not break this contract and avoids
instantiating the bean. Instead, it registers a proxy with the MBeanServer and
defers obtaining the bean from the container until the first invocation on the proxy
occurs.
Any beans that are exported through the MBeanExporter and are already valid MBeans are
registered as-is with the MBeanServer without further intervention from Spring. You can cause MBeans
to be automatically detected by the MBeanExporter by setting the autodetect
property to true, as the following example shows:
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="autodetect" value="true"/>
</bean>
<bean name="spring:mbean=true" class="org.springframework.jmx.export.TestDynamicMBean"/>In the preceding example, the bean called spring:mbean=true is already a valid JMX MBean
and is automatically registered by Spring. By default, a bean that is autodetected for JMX
registration has its bean name used as the ObjectName. You can override this behavior,
as detailed in Controlling ObjectName Instances for Your Beans.
Consider the scenario where a Spring MBeanExporter attempts to register an MBean
with an MBeanServer by using the ObjectName bean:name=testBean1. If an MBean
instance has already been registered under that same ObjectName, the default behavior
is to fail (and throw an InstanceAlreadyExistsException).
You can control exactly what happens when an MBean is
registered with an MBeanServer. Spring’s JMX support allows for three different
registration behaviors to control the registration behavior when the registration
process finds that an MBean has already been registered under the same ObjectName.
The following table summarizes these registration behaviors:
| Registration behavior | Explanation |
|---|---|
|
This is the default registration behavior. If an |
|
If an |
|
If an |
The values in the preceding table are defined as enums on the RegistrationPolicy class.
If you want to change the default registration behavior, you need to set the value of the
registrationPolicy property on your MBeanExporter definition to one of those
values.
The following example shows how to change from the default registration
behavior to the REPLACE_EXISTING behavior:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean1" value-ref="testBean"/>
</map>
</property>
<property name="registrationPolicy" value="REPLACE_EXISTING"/>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>In the example in the preceding section,
you had little control over the management interface of your bean. All of the public
properties and methods of each exported bean were exposed as JMX attributes and
operations, respectively. To exercise finer-grained control over exactly which
properties and methods of your exported beans are actually exposed as JMX attributes
and operations, Spring JMX provides a comprehensive and extensible mechanism for
controlling the management interfaces of your beans.
Behind the scenes, the MBeanExporter delegates to an implementation of the
org.springframework.jmx.export.assembler.MBeanInfoAssembler interface, which is
responsible for defining the management interface of each bean that is exposed.
The default implementation,
org.springframework.jmx.export.assembler.SimpleReflectiveMBeanInfoAssembler,
defines a management interface that exposes all public properties and methods
(as you saw in the examples in the preceding sections). Spring provides two
additional implementations of the MBeanInfoAssembler interface that let you
control the generated management interface by using either source-level metadata
or any arbitrary interface.
By using the MetadataMBeanInfoAssembler, you can define the management interfaces
for your beans by using source-level metadata. The reading of metadata is encapsulated
by the org.springframework.jmx.export.metadata.JmxAttributeSource interface.
Spring JMX provides a default implementation that uses Java annotations, namely
org.springframework.jmx.export.annotation.AnnotationJmxAttributeSource.
You must configure the MetadataMBeanInfoAssembler with an implementation instance of
the JmxAttributeSource interface for it to function correctly (there is no default).
To mark a bean for export to JMX, you should annotate the bean class with the
ManagedResource annotation. You must mark each method you wish to expose as an operation
with the ManagedOperation annotation and mark each property you wish to expose
with the ManagedAttribute annotation. When marking properties, you can omit
either the annotation of the getter or the setter to create a write-only or read-only
attribute, respectively.
|
Note
|
A ManagedResource-annotated bean must be public, as must the methods exposing
an operation or an attribute.
|
The following example shows the annotated version of the JmxTestBean class that we
used in Creating an MBeanServer:
package org.springframework.jmx;
import org.springframework.jmx.export.annotation.ManagedResource;
import org.springframework.jmx.export.annotation.ManagedOperation;
import org.springframework.jmx.export.annotation.ManagedAttribute;
@ManagedResource(
objectName="bean:name=testBean4",
description="My Managed Bean",
log=true,
logFile="jmx.log",
currencyTimeLimit=15,
persistPolicy="OnUpdate",
persistPeriod=200,
persistLocation="foo",
persistName="bar")
public class AnnotationTestBean implements IJmxTestBean {
private String name;
private int age;
@ManagedAttribute(description="The Age Attribute", currencyTimeLimit=15)
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@ManagedAttribute(description="The Name Attribute",
currencyTimeLimit=20,
defaultValue="bar",
persistPolicy="OnUpdate")
public void setName(String name) {
this.name = name;
}
@ManagedAttribute(defaultValue="foo", persistPeriod=300)
public String getName() {
return name;
}
@ManagedOperation(description="Add two numbers")
@ManagedOperationParameters({
@ManagedOperationParameter(name = "x", description = "The first number"),
@ManagedOperationParameter(name = "y", description = "The second number")})
public int add(int x, int y) {
return x + y;
}
public void dontExposeMe() {
throw new RuntimeException();
}
}In the preceding example, you can see that the JmxTestBean class is marked with the
ManagedResource annotation and that this ManagedResource annotation is configured
with a set of properties. These properties can be used to configure various aspects
of the MBean that is generated by the MBeanExporter and are explained in greater
detail later in Source-level Metadata Types.
Both the age and name properties are annotated with the ManagedAttribute
annotation, but, in the case of the age property, only the getter is marked.
This causes both of these properties to be included in the management interface
as attributes, but the age attribute is read-only.
Finally, the add(int, int) method is marked with the ManagedOperation attribute,
whereas the dontExposeMe() method is not. This causes the management interface to
contain only one operation (add(int, int)) when you use the MetadataMBeanInfoAssembler.
The following configuration shows how you can configure the MBeanExporter to use the
MetadataMBeanInfoAssembler:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="assembler" ref="assembler"/>
<property name="namingStrategy" ref="namingStrategy"/>
<property name="autodetect" value="true"/>
</bean>
<bean id="jmxAttributeSource"
class="org.springframework.jmx.export.annotation.AnnotationJmxAttributeSource"/>
<!-- will create management interface using annotation metadata -->
<bean id="assembler"
class="org.springframework.jmx.export.assembler.MetadataMBeanInfoAssembler">
<property name="attributeSource" ref="jmxAttributeSource"/>
</bean>
<!-- will pick up the ObjectName from the annotation -->
<bean id="namingStrategy"
class="org.springframework.jmx.export.naming.MetadataNamingStrategy">
<property name="attributeSource" ref="jmxAttributeSource"/>
</bean>
<bean id="testBean" class="org.springframework.jmx.AnnotationTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>In the preceding example, an MetadataMBeanInfoAssembler bean has been configured with an
instance of the AnnotationJmxAttributeSource class and passed to the MBeanExporter
through the assembler property. This is all that is required to take advantage of
metadata-driven management interfaces for your Spring-exposed MBeans.
The following table describes the source-level metadata types that are available for use in Spring JMX:
| Purpose | Annotation | Annotation Type |
|---|---|---|
Mark all instances of a |
|
Class |
Mark a method as a JMX operation. |
|
Method |
Mark a getter or setter as one half of a JMX attribute. |
|
Method (only getters and setters) |
Define descriptions for operation parameters. |
|
Method |
The following table describes the configuration parameters that are available for use on these source-level metadata types:
| Parameter | Description | Applies to |
|---|---|---|
|
Used by |
|
|
Sets the friendly description of the resource, attribute or operation. |
|
|
Sets the value of the |
|
|
Sets the value of the |
|
|
Sets the value of the |
|
|
Sets the value of the |
|
|
Sets the value of the |
|
|
Sets the value of the |
|
|
Sets the value of the |
|
|
Sets the value of the |
|
|
Sets the display name of an operation parameter. |
|
|
Sets the index of an operation parameter. |
|
To simplify configuration even further, Spring includes the
AutodetectCapableMBeanInfoAssembler interface, which extends the MBeanInfoAssembler
interface to add support for autodetection of MBean resources. If you configure the
MBeanExporter with an instance of AutodetectCapableMBeanInfoAssembler, it is
allowed to “vote” on the inclusion of beans for exposure to JMX.
The only implementation of the AutodetectCapableMBeanInfo interface is
the MetadataMBeanInfoAssembler, which votes to include any bean that is marked
with the ManagedResource attribute. The default approach in this case is to use the
bean name as the ObjectName, which results in a configuration similar to the following:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<!-- notice how no 'beans' are explicitly configured here -->
<property name="autodetect" value="true"/>
<property name="assembler" ref="assembler"/>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
<bean id="assembler" class="org.springframework.jmx.export.assembler.MetadataMBeanInfoAssembler">
<property name="attributeSource">
<bean class="org.springframework.jmx.export.annotation.AnnotationJmxAttributeSource"/>
</property>
</bean>
</beans>Notice that, in the preceding configuration, no beans are passed to the MBeanExporter.
However, the JmxTestBean is still registered, since it is marked with the ManagedResource
attribute and the MetadataMBeanInfoAssembler detects this and votes to include it.
The only problem with this approach is that the name of the JmxTestBean now has business
meaning. You can address this issue by changing the default behavior for ObjectName
creation as defined in Controlling ObjectName Instances for Your Beans.
In addition to the MetadataMBeanInfoAssembler, Spring also includes the
InterfaceBasedMBeanInfoAssembler, which lets you constrain the methods and
properties that are exposed based on the set of methods defined in a collection of
interfaces.
Although the standard mechanism for exposing MBeans is to use interfaces and a simple
naming scheme, InterfaceBasedMBeanInfoAssembler extends this functionality by
removing the need for naming conventions, letting you use more than one interface
and removing the need for your beans to implement the MBean interfaces.
Consider the following interface, which is used to define a management interface for the
JmxTestBean class that we showed earlier:
public interface IJmxTestBean {
public int add(int x, int y);
public long myOperation();
public int getAge();
public void setAge(int age);
public void setName(String name);
public String getName();
}This interface defines the methods and properties that are exposed as operations and attributes on the JMX MBean. The following code shows how to configure Spring JMX to use this interface as the definition for the management interface:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean5" value-ref="testBean"/>
</map>
</property>
<property name="assembler">
<bean class="org.springframework.jmx.export.assembler.InterfaceBasedMBeanInfoAssembler">
<property name="managedInterfaces">
<value>org.springframework.jmx.IJmxTestBean</value>
</property>
</bean>
</property>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>In the preceding example, the InterfaceBasedMBeanInfoAssembler is configured to use the
IJmxTestBean interface when constructing the management interface for any bean. It is
important to understand that beans processed by the InterfaceBasedMBeanInfoAssembler
are not required to implement the interface used to generate the JMX management
interface.
In the preceding case, the IJmxTestBean interface is used to construct all management
interfaces for all beans. In many cases, this is not the desired behavior, and you may
want to use different interfaces for different beans. In this case, you can pass
InterfaceBasedMBeanInfoAssembler a Properties instance through the interfaceMappings
property, where the key of each entry is the bean name and the value of each entry is a
comma-separated list of interface names to use for that bean.
If no management interface is specified through either the managedInterfaces or
interfaceMappings properties, the InterfaceBasedMBeanInfoAssembler reflects
on the bean and uses all of the interfaces implemented by that bean to create the
management interface.
MethodNameBasedMBeanInfoAssembler lets you specify a list of method names
that are exposed to JMX as attributes and operations. The following code shows a sample
configuration:
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean5" value-ref="testBean"/>
</map>
</property>
<property name="assembler">
<bean class="org.springframework.jmx.export.assembler.MethodNameBasedMBeanInfoAssembler">
<property name="managedMethods">
<value>add,myOperation,getName,setName,getAge</value>
</property>
</bean>
</property>
</bean>In the preceding example, you can see that the add and myOperation methods are exposed as JMX
operations, and getName(), setName(String), and getAge() are exposed as the
appropriate half of a JMX attribute. In the preceding code, the method mappings apply to
beans that are exposed to JMX. To control method exposure on a bean-by-bean basis, you can use
the methodMappings property of MethodNameMBeanInfoAssembler to map bean names to
lists of method names.
Behind the scenes, the MBeanExporter delegates to an implementation of the
ObjectNamingStrategy to obtain an ObjectName instance for each of the beans it registers.
By default, the default implementation, KeyNamingStrategy uses the key of the
beans Map as the ObjectName. In addition, the KeyNamingStrategy can map the key
of the beans Map to an entry in a Properties file (or files) to resolve the
ObjectName. In addition to the KeyNamingStrategy, Spring provides two additional
ObjectNamingStrategy implementations: the IdentityNamingStrategy (which builds an
ObjectName based on the JVM identity of the bean) and the MetadataNamingStrategy (which
uses source-level metadata to obtain the ObjectName).
You can configure your own KeyNamingStrategy instance and configure it to read
ObjectName instances from a Properties instance rather than use a bean key. The
KeyNamingStrategy tries to locate an entry in the Properties with a key
that corresponds to the bean key. If no entry is found or if the Properties instance is
null, the bean key itself is used.
The following code shows a sample configuration for the KeyNamingStrategy:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="testBean" value-ref="testBean"/>
</map>
</property>
<property name="namingStrategy" ref="namingStrategy"/>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
<bean id="namingStrategy" class="org.springframework.jmx.export.naming.KeyNamingStrategy">
<property name="mappings">
<props>
<prop key="testBean">bean:name=testBean1</prop>
</props>
</property>
<property name="mappingLocations">
<value>names1.properties,names2.properties</value>
</property>
</bean>
</beans>The preceding example configures an instance of KeyNamingStrategy with a Properties instance that
is merged from the Properties instance defined by the mapping property and the
properties files located in the paths defined by the mappings property. In this
configuration, the testBean bean is given an ObjectName of bean:name=testBean1,
since this is the entry in the Properties instance that has a key corresponding to the
bean key.
If no entry in the Properties instance can be found, the bean key name is used as
the ObjectName.
MetadataNamingStrategy uses the objectName property of the ManagedResource
attribute on each bean to create the ObjectName. The following code shows the
configuration for the MetadataNamingStrategy:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="testBean" value-ref="testBean"/>
</map>
</property>
<property name="namingStrategy" ref="namingStrategy"/>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
<bean id="namingStrategy" class="org.springframework.jmx.export.naming.MetadataNamingStrategy">
<property name="attributeSource" ref="attributeSource"/>
</bean>
<bean id="attributeSource"
class="org.springframework.jmx.export.annotation.AnnotationJmxAttributeSource"/>
</beans>If no objectName has been provided for the ManagedResource attribute, an
ObjectName is created with the following
format: [fully-qualified-package-name]:type=[short-classname],name=[bean-name]. For
example, the generated ObjectName for the following bean would be
com.example:type=MyClass,name=myBean:
<bean id="myBean" class="com.example.MyClass"/>If you prefer to use the annotation-based approach to define
your management interfaces, a convenience subclass of MBeanExporter is available:
AnnotationMBeanExporter. When defining an instance of this subclass, you no longer need the
namingStrategy, assembler, and attributeSource configuration,
since it always uses standard Java annotation-based metadata (autodetection is
always enabled as well). In fact, rather than defining an MBeanExporter bean, an even
simpler syntax is supported by the @EnableMBeanExport @Configuration annotation,
as the following example shows:
@Configuration
@EnableMBeanExport
public class AppConfig {
}If you prefer XML-based configuration, the <context:mbean-export/> element serves the
same purpose and is shown in the following listing:
<context:mbean-export/>If necessary, you can provide a reference to a particular MBean server, and the
defaultDomain attribute (a property of AnnotationMBeanExporter) accepts an alternate
value for the generated MBean ObjectName domains. This is used in place of the
fully qualified package name as described in the previous section on
MetadataNamingStrategy, as the following example shows:
@EnableMBeanExport(server="myMBeanServer", defaultDomain="myDomain")
@Configuration
ContextConfiguration {
}The following example shows the XML equivalent of the preceding annotation-based example:
<context:mbean-export server="myMBeanServer" default-domain="myDomain"/>|
Caution
|
Do not use interface-based AOP proxies in combination with autodetection of JMX
annotations in your bean classes. Interface-based proxies “hide” the target class, which
also hides the JMX-managed resource annotations. Hence, you should use target-class proxies in that
case (through setting the 'proxy-target-class' flag on <aop:config/>,
<tx:annotation-driven/> and so on). Otherwise, your JMX beans might be silently ignored at
startup.
|
For remote access, Spring JMX module offers two FactoryBean implementations inside the
org.springframework.jmx.support package for creating both server- and client-side
connectors.
To have Spring JMX create, start, and expose a JSR-160 JMXConnectorServer, you can use the
following configuration:
<bean id="serverConnector" class="org.springframework.jmx.support.ConnectorServerFactoryBean"/>By default, ConnectorServerFactoryBean creates a JMXConnectorServer bound to
service:jmx:jmxmp://localhost:9875. The serverConnector bean thus exposes the
local MBeanServer to clients through the JMXMP protocol on localhost, port 9875. Note
that the JMXMP protocol is marked as optional by the JSR 160 specification. Currently,
the main open-source JMX implementation, MX4J, and the one provided with the JDK
do not support JMXMP.
To specify another URL and register the JMXConnectorServer itself with the
MBeanServer, you can use the serviceUrl and ObjectName properties, respectively,
as the following example shows:
<bean id="serverConnector"
class="org.springframework.jmx.support.ConnectorServerFactoryBean">
<property name="objectName" value="connector:name=rmi"/>
<property name="serviceUrl"
value="service:jmx:rmi://localhost/jndi/rmi://localhost:1099/myconnector"/>
</bean>If the ObjectName property is set, Spring automatically registers your connector
with the MBeanServer under that ObjectName. The following example shows the full set of
parameters that you can pass to the ConnectorServerFactoryBean when creating a
JMXConnector:
<bean id="serverConnector"
class="org.springframework.jmx.support.ConnectorServerFactoryBean">
<property name="objectName" value="connector:name=iiop"/>
<property name="serviceUrl"
value="service:jmx:iiop://localhost/jndi/iiop://localhost:900/myconnector"/>
<property name="threaded" value="true"/>
<property name="daemon" value="true"/>
<property name="environment">
<map>
<entry key="someKey" value="someValue"/>
</map>
</property>
</bean>Note that, when you use a RMI-based connector, you need the lookup service (tnameserv or
rmiregistry) to be started in order for the name registration to complete. If you
use Spring to export remote services for you through RMI, Spring has already
constructed an RMI registry. If not, you can easily start a registry by using the following
snippet of configuration:
<bean id="registry" class="org.springframework.remoting.rmi.RmiRegistryFactoryBean">
<property name="port" value="1099"/>
</bean>To create an MBeanServerConnection to a remote JSR-160-enabled MBeanServer, you can use the
MBeanServerConnectionFactoryBean, as the following example shows:
<bean id="clientConnector" class="org.springframework.jmx.support.MBeanServerConnectionFactoryBean">
<property name="serviceUrl" value="service:jmx:rmi://localhost/jndi/rmi://localhost:1099/jmxrmi"/>
</bean>JSR-160 permits extensions to the way in which communication is done between the client and the server. The examples shown in the preceding sections use the mandatory RMI-based implementation required by the JSR-160 specification (IIOP and JRMP) and the (optional) JMXMP. By using other providers or JMX implementations (such as MX4J) you can take advantage of protocols such as SOAP or Hessian over simple HTTP or SSL and others, as the following example shows:
<bean id="serverConnector" class="org.springframework.jmx.support.ConnectorServerFactoryBean">
<property name="objectName" value="connector:name=burlap"/>
<property name="serviceUrl" value="service:jmx:burlap://localhost:9874"/>
</bean>In the preceding example, we used MX4J 3.0.0. See the official MX4J documentation for more information.
Spring JMX lets you create proxies that re-route calls to MBeans that are registered in a
local or remote MBeanServer. These proxies provide you with a standard Java interface,
through which you can interact with your MBeans. The following code shows how to configure a
proxy for an MBean running in a local MBeanServer:
<bean id="proxy" class="org.springframework.jmx.access.MBeanProxyFactoryBean">
<property name="objectName" value="bean:name=testBean"/>
<property name="proxyInterface" value="org.springframework.jmx.IJmxTestBean"/>
</bean>In the preceding example, you can see that a proxy is created for the MBean registered under the
ObjectName of bean:name=testBean. The set of interfaces that the proxy implements
is controlled by the proxyInterfaces property, and the rules for mapping methods and
properties on these interfaces to operations and attributes on the MBean are the same
rules used by the InterfaceBasedMBeanInfoAssembler.
The MBeanProxyFactoryBean can create a proxy to any MBean that is accessible through an
MBeanServerConnection. By default, the local MBeanServer is located and used, but
you can override this and provide an MBeanServerConnection that points to a remote
MBeanServer to cater for proxies that point to remote MBeans:
<bean id="clientConnector"
class="org.springframework.jmx.support.MBeanServerConnectionFactoryBean">
<property name="serviceUrl" value="service:jmx:rmi://remotehost:9875"/>
</bean>
<bean id="proxy" class="org.springframework.jmx.access.MBeanProxyFactoryBean">
<property name="objectName" value="bean:name=testBean"/>
<property name="proxyInterface" value="org.springframework.jmx.IJmxTestBean"/>
<property name="server" ref="clientConnector"/>
</bean>In the preceding example, we create an MBeanServerConnection that points to a remote machine
that uses the MBeanServerConnectionFactoryBean. This MBeanServerConnection is then
passed to the MBeanProxyFactoryBean through the server property. The proxy that is
created forwards all invocations to the MBeanServer through this
MBeanServerConnection.
Spring’s JMX offering includes comprehensive support for JMX notifications.
Spring’s JMX support makes it easy to register any number of
NotificationListeners with any number of MBeans (this includes MBeans exported by
Spring’s MBeanExporter and MBeans registered through some other mechanism). For
example, consider the scenario where one would like to be informed (through a
Notification) each and every time an attribute of a target MBean changes. The following
example writes notifications to the console:
package com.example;
import javax.management.AttributeChangeNotification;
import javax.management.Notification;
import javax.management.NotificationFilter;
import javax.management.NotificationListener;
public class ConsoleLoggingNotificationListener
implements NotificationListener, NotificationFilter {
public void handleNotification(Notification notification, Object handback) {
System.out.println(notification);
System.out.println(handback);
}
public boolean isNotificationEnabled(Notification notification) {
return AttributeChangeNotification.class.isAssignableFrom(notification.getClass());
}
}The following example adds ConsoleLoggingNotificationListener (defined in the preceding
example) to notificationListenerMappings:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean1" value-ref="testBean"/>
</map>
</property>
<property name="notificationListenerMappings">
<map>
<entry key="bean:name=testBean1">
<bean class="com.example.ConsoleLoggingNotificationListener"/>
</entry>
</map>
</property>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>With the preceding configuration in place, every time a JMX Notification is broadcast from
the target MBean (bean:name=testBean1), the ConsoleLoggingNotificationListener bean
that was registered as a listener through the notificationListenerMappings property is
notified. The ConsoleLoggingNotificationListener bean can then take whatever action
it deems appropriate in response to the Notification.
You can also use straight bean names as the link between exported beans and listeners, as the following example shows:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean1" value-ref="testBean"/>
</map>
</property>
<property name="notificationListenerMappings">
<map>
<entry key="testBean">
<bean class="com.example.ConsoleLoggingNotificationListener"/>
</entry>
</map>
</property>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>If you want to register a single NotificationListener instance for all of the beans
that the enclosing MBeanExporter exports, you can use the special wildcard (*)
as the key for an entry in the notificationListenerMappings property
map, as the following example shows:
<property name="notificationListenerMappings">
<map>
<entry key="*">
<bean class="com.example.ConsoleLoggingNotificationListener"/>
</entry>
</map>
</property>If you need to do the inverse (that is, register a number of distinct listeners against
an MBean), you must instead use the notificationListeners list property (in
preference to the notificationListenerMappings property). This time, instead of
configuring a NotificationListener for a single MBean, we configure
NotificationListenerBean instances. A NotificationListenerBean encapsulates a
NotificationListener and the ObjectName (or ObjectNames) that it is to be
registered against in an MBeanServer. The NotificationListenerBean also encapsulates
a number of other properties, such as a NotificationFilter and an arbitrary handback
object that can be used in advanced JMX notification scenarios.
The configuration when using NotificationListenerBean instances is not wildly
different to what was presented previously, as the following example shows:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean1" value-ref="testBean"/>
</map>
</property>
<property name="notificationListeners">
<list>
<bean class="org.springframework.jmx.export.NotificationListenerBean">
<constructor-arg>
<bean class="com.example.ConsoleLoggingNotificationListener"/>
</constructor-arg>
<property name="mappedObjectNames">
<list>
<value>bean:name=testBean1</value>
</list>
</property>
</bean>
</list>
</property>
</bean>
<bean id="testBean" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
</beans>The preceding example is equivalent to the first notification example. Assume, then, that
we want to be given a handback object every time a Notification is raised and that
we also want to filter out extraneous Notifications by supplying a
NotificationFilter. The following example accomplishes these goals:
<beans>
<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
<property name="beans">
<map>
<entry key="bean:name=testBean1" value-ref="testBean1"/>
<entry key="bean:name=testBean2" value-ref="testBean2"/>
</map>
</property>
<property name="notificationListeners">
<list>
<bean class="org.springframework.jmx.export.NotificationListenerBean">
<constructor-arg ref="customerNotificationListener"/>
<property name="mappedObjectNames">
<list>
<!-- handles notifications from two distinct MBeans -->
<value>bean:name=testBean1</value>
<value>bean:name=testBean2</value>
</list>
</property>
<property name="handback">
<bean class="java.lang.String">
<constructor-arg value="This could be anything..."/>
</bean>
</property>
<property name="notificationFilter" ref="customerNotificationListener"/>
</bean>
</list>
</property>
</bean>
<!-- implements both the NotificationListener and NotificationFilter interfaces -->
<bean id="customerNotificationListener" class="com.example.ConsoleLoggingNotificationListener"/>
<bean id="testBean1" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="TEST"/>
<property name="age" value="100"/>
</bean>
<bean id="testBean2" class="org.springframework.jmx.JmxTestBean">
<property name="name" value="ANOTHER TEST"/>
<property name="age" value="200"/>
</bean>
</beans>(For a full discussion of what a handback object is and,
indeed, what a NotificationFilter is, see the section of the JMX
specification (1.2) entitled 'The JMX Notification Model'.)
Spring provides support not only for registering to receive Notifications but also
for publishing Notifications.
|
Note
|
This section is really only relevant to Spring-managed beans that have
been exposed as MBeans through an MBeanExporter. Any existing user-defined MBeans should
use the standard JMX APIs for notification publication.
|
The key interface in Spring’s JMX notification publication support is the
NotificationPublisher interface (defined in the
org.springframework.jmx.export.notification package). Any bean that is going to be
exported as an MBean through an MBeanExporter instance can implement the related
NotificationPublisherAware interface to gain access to a NotificationPublisher
instance. The NotificationPublisherAware interface supplies an instance of a
NotificationPublisher to the implementing bean through a simple setter method,
which the bean can then use to publish Notifications.
As stated in the javadoc of the
{api-spring-framework}/jmx/export/notification/NotificationPublisher.html[NotificationPublisher]
interface, managed beans that publish events through the NotificationPublisher
mechanism are not responsible for the state management of notification listeners.
Spring’s JMX support takes care of handling all the JMX infrastructure issues.
All you need to do, as an application developer, is implement the
NotificationPublisherAware interface and start publishing events by using the
supplied NotificationPublisher instance. Note that the NotificationPublisher
is set after the managed bean has been registered with an MBeanServer.
Using a NotificationPublisher instance is quite straightforward. You create a JMX
Notification instance (or an instance of an appropriate Notification subclass),
populate the notification with the data pertinent to the event that is to be
published, and invoke the sendNotification(Notification) on the
NotificationPublisher instance, passing in the Notification.
In the following example, exported instances of the JmxTestBean publish a
NotificationEvent every time the add(int, int) operation is invoked:
package org.springframework.jmx;
import org.springframework.jmx.export.notification.NotificationPublisherAware;
import org.springframework.jmx.export.notification.NotificationPublisher;
import javax.management.Notification;
public class JmxTestBean implements IJmxTestBean, NotificationPublisherAware {
private String name;
private int age;
private boolean isSuperman;
private NotificationPublisher publisher;
// other getters and setters omitted for clarity
public int add(int x, int y) {
int answer = x + y;
this.publisher.sendNotification(new Notification("add", this, 0));
return answer;
}
public void dontExposeMe() {
throw new RuntimeException();
}
public void setNotificationPublisher(NotificationPublisher notificationPublisher) {
this.publisher = notificationPublisher;
}
}The NotificationPublisher interface and the machinery to get it all working is one of
the nicer features of Spring’s JMX support. It does, however, come with the price tag of
coupling your classes to both Spring and JMX. As always, the advice here is to be
pragmatic. If you need the functionality offered by the NotificationPublisher and
you can accept the coupling to both Spring and JMX, then do so.
This section contains links to further resources about JMX:
-
The JMX homepage at Oracle.
-
The JMX specification (JSR-000003).
-
The JMX Remote API specification (JSR-000160).
-
The MX4J homepage. (MX4J is an open-source implementation of various JMX specs.)
This section describes how to send email with the Spring Framework.
The following JAR needs to be on the classpath of your application in order to use the Spring Framework’s email library:
-
The JavaMail / Jakarta Mail 1.6 library
This library is freely available on the web — for example, in Maven Central as
com.sun.mail:jakarta.mail. Please make sure to use the latest 1.6.x version
rather than Jakarta Mail 2.0 (which comes with a different package namespace).
The Spring Framework provides a helpful utility library for sending email that shields you from the specifics of the underlying mailing system and is responsible for low-level resource handling on behalf of the client.
The org.springframework.mail package is the root level package for the Spring
Framework’s email support. The central interface for sending emails is the MailSender
interface. A simple value object that encapsulates the properties of a simple mail such
as from and to (plus many others) is the SimpleMailMessage class. This package
also contains a hierarchy of checked exceptions that provide a higher level of
abstraction over the lower level mail system exceptions, with the root exception being
MailException. See the {api-spring-framework}/mail/MailException.html[javadoc]
for more information on the rich mail exception hierarchy.
The org.springframework.mail.javamail.JavaMailSender interface adds specialized
JavaMail features, such as MIME message support to the MailSender interface
(from which it inherits). JavaMailSender also provides a callback interface called
org.springframework.mail.javamail.MimeMessagePreparator for preparing a MimeMessage.
Assume that we have a business interface called OrderManager, as the following example shows:
public interface OrderManager {
void placeOrder(Order order);
}Further assume that we have a requirement stating that an email message with an order number needs to be generated and sent to a customer who placed the relevant order.
The following example shows how to use MailSender and SimpleMailMessage to send an
email when someone places an order:
import org.springframework.mail.MailException;
import org.springframework.mail.MailSender;
import org.springframework.mail.SimpleMailMessage;
public class SimpleOrderManager implements OrderManager {
private MailSender mailSender;
private SimpleMailMessage templateMessage;
public void setMailSender(MailSender mailSender) {
this.mailSender = mailSender;
}
public void setTemplateMessage(SimpleMailMessage templateMessage) {
this.templateMessage = templateMessage;
}
public void placeOrder(Order order) {
// Do the business calculations...
// Call the collaborators to persist the order...
// Create a thread safe "copy" of the template message and customize it
SimpleMailMessage msg = new SimpleMailMessage(this.templateMessage);
msg.setTo(order.getCustomer().getEmailAddress());
msg.setText(
"Dear " + order.getCustomer().getFirstName()
+ order.getCustomer().getLastName()
+ ", thank you for placing order. Your order number is "
+ order.getOrderNumber());
try {
this.mailSender.send(msg);
}
catch (MailException ex) {
// simply log it and go on...
System.err.println(ex.getMessage());
}
}
}The following example shows the bean definitions for the preceding code:
<bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">
<property name="host" value="mail.mycompany.example"/>
</bean>
<!-- this is a template message that we can pre-load with default state -->
<bean id="templateMessage" class="org.springframework.mail.SimpleMailMessage">
<property name="from" value="[email protected]"/>
<property name="subject" value="Your order"/>
</bean>
<bean id="orderManager" class="com.mycompany.businessapp.support.SimpleOrderManager">
<property name="mailSender" ref="mailSender"/>
<property name="templateMessage" ref="templateMessage"/>
</bean>This section describes another implementation of OrderManager that uses the MimeMessagePreparator
callback interface. In the following example, the mailSender property is of type
JavaMailSender so that we are able to use the JavaMail MimeMessage class:
import jakarta.mail.Message;
import jakarta.mail.MessagingException;
import jakarta.mail.internet.InternetAddress;
import jakarta.mail.internet.MimeMessage;
import jakarta.mail.internet.MimeMessage;
import org.springframework.mail.MailException;
import org.springframework.mail.javamail.JavaMailSender;
import org.springframework.mail.javamail.MimeMessagePreparator;
public class SimpleOrderManager implements OrderManager {
private JavaMailSender mailSender;
public void setMailSender(JavaMailSender mailSender) {
this.mailSender = mailSender;
}
public void placeOrder(final Order order) {
// Do the business calculations...
// Call the collaborators to persist the order...
MimeMessagePreparator preparator = new MimeMessagePreparator() {
public void prepare(MimeMessage mimeMessage) throws Exception {
mimeMessage.setRecipient(Message.RecipientType.TO,
new InternetAddress(order.getCustomer().getEmailAddress()));
mimeMessage.setFrom(new InternetAddress("[email protected]"));
mimeMessage.setText("Dear " + order.getCustomer().getFirstName() + " " +
order.getCustomer().getLastName() + ", thanks for your order. " +
"Your order number is " + order.getOrderNumber() + ".");
}
};
try {
this.mailSender.send(preparator);
}
catch (MailException ex) {
// simply log it and go on...
System.err.println(ex.getMessage());
}
}
}|
Note
|
The mail code is a crosscutting concern and could well be a candidate for
refactoring into a custom Spring AOP aspect, which could then
be run at appropriate joinpoints on the OrderManager target.
|
The Spring Framework’s mail support ships with the standard JavaMail implementation. See the relevant javadoc for more information.
A class that comes in pretty handy when dealing with JavaMail messages is
org.springframework.mail.javamail.MimeMessageHelper, which shields you from
having to use the verbose JavaMail API. Using the MimeMessageHelper, it is
pretty easy to create a MimeMessage, as the following example shows:
// of course you would use DI in any real-world cases
JavaMailSenderImpl sender = new JavaMailSenderImpl();
sender.setHost("mail.host.com");
MimeMessage message = sender.createMimeMessage();
MimeMessageHelper helper = new MimeMessageHelper(message);
helper.setTo("[email protected]");
helper.setText("Thank you for ordering!");
sender.send(message);Multipart email messages allow for both attachments and inline resources. Examples of inline resources include an image or a stylesheet that you want to use in your message but that you do not want displayed as an attachment.
The following example shows you how to use the MimeMessageHelper to send an email
with a single JPEG image attachment:
JavaMailSenderImpl sender = new JavaMailSenderImpl();
sender.setHost("mail.host.com");
MimeMessage message = sender.createMimeMessage();
// use the true flag to indicate you need a multipart message
MimeMessageHelper helper = new MimeMessageHelper(message, true);
helper.setTo("[email protected]");
helper.setText("Check out this image!");
// let's attach the infamous windows Sample file (this time copied to c:/)
FileSystemResource file = new FileSystemResource(new File("c:/Sample.jpg"));
helper.addAttachment("CoolImage.jpg", file);
sender.send(message);The following example shows you how to use the MimeMessageHelper to send an email
with an inline image:
JavaMailSenderImpl sender = new JavaMailSenderImpl();
sender.setHost("mail.host.com");
MimeMessage message = sender.createMimeMessage();
// use the true flag to indicate you need a multipart message
MimeMessageHelper helper = new MimeMessageHelper(message, true);
helper.setTo("[email protected]");
// use the true flag to indicate the text included is HTML
helper.setText("<html><body><img src='cid:identifier1234'></body></html>", true);
// let's include the infamous windows Sample file (this time copied to c:/)
FileSystemResource res = new FileSystemResource(new File("c:/Sample.jpg"));
helper.addInline("identifier1234", res);
sender.send(message);|
Warning
|
Inline resources are added to the MimeMessage by using the specified Content-ID
(identifier1234 in the above example). The order in which you add the text
and the resource are very important. Be sure to first add the text and then
the resources. If you are doing it the other way around, it does not work.
|
The code in the examples shown in the previous sections explicitly created the content of the email message,
by using methods calls such as message.setText(..). This is fine for simple cases, and it
is okay in the context of the aforementioned examples, where the intent was to show you
the very basics of the API.
In your typical enterprise application, though, developers often do not create the content of email messages by using the previously shown approach for a number of reasons:
-
Creating HTML-based email content in Java code is tedious and error prone.
-
There is no clear separation between display logic and business logic.
-
Changing the display structure of the email content requires writing Java code, recompiling, redeploying, and so on.
Typically, the approach taken to address these issues is to use a template library (such as FreeMarker) to define the display structure of email content. This leaves your code tasked only with creating the data that is to be rendered in the email template and sending the email. It is definitely a best practice when the content of your email messages becomes even moderately complex, and, with the Spring Framework’s support classes for FreeMarker, it becomes quite easy to do.
The Spring Framework provides abstractions for the asynchronous execution and scheduling of
tasks with the TaskExecutor and TaskScheduler interfaces, respectively. Spring also
features implementations of those interfaces that support thread pools or delegation to
CommonJ within an application server environment. Ultimately, the use of these
implementations behind the common interfaces abstracts away the differences between Java
SE 5, Java SE 6, and Jakarta EE environments.
Spring also features integration classes to support scheduling with the Timer
(part of the JDK since 1.3) and the Quartz Scheduler ( https://www.quartz-scheduler.org/).
You can set up both of those schedulers by using a FactoryBean with optional references to
Timer or Trigger instances, respectively. Furthermore, a convenience class for both
the Quartz Scheduler and the Timer is available that lets you invoke a method of
an existing target object (analogous to the normal MethodInvokingFactoryBean
operation).
Executors are the JDK name for the concept of thread pools. The “executor” naming is due to the fact that there is no guarantee that the underlying implementation is actually a pool. An executor may be single-threaded or even synchronous. Spring’s abstraction hides implementation details between the Java SE and Jakarta EE environments.
Spring’s TaskExecutor interface is identical to the java.util.concurrent.Executor
interface. In fact, originally, its primary reason for existence was to abstract away
the need for Java 5 when using thread pools. The interface has a single method
(execute(Runnable task)) that accepts a task for execution based on the semantics
and configuration of the thread pool.
The TaskExecutor was originally created to give other Spring components an abstraction
for thread pooling where needed. Components such as the ApplicationEventMulticaster,
JMS’s AbstractMessageListenerContainer, and Quartz integration all use the
TaskExecutor abstraction to pool threads. However, if your beans need thread pooling
behavior, you can also use this abstraction for your own needs.
Spring includes a number of pre-built implementations of TaskExecutor.
In all likelihood, you should never need to implement your own.
The variants that Spring provides are as follows:
-
SyncTaskExecutor: This implementation does not run invocations asynchronously. Instead, each invocation takes place in the calling thread. It is primarily used in situations where multi-threading is not necessary, such as in simple test cases. -
SimpleAsyncTaskExecutor: This implementation does not reuse any threads. Rather, it starts up a new thread for each invocation. However, it does support a concurrency limit that blocks any invocations that are over the limit until a slot has been freed up. If you are looking for true pooling, seeThreadPoolTaskExecutor, later in this list. -
ConcurrentTaskExecutor: This implementation is an adapter for ajava.util.concurrent.Executorinstance. There is an alternative (ThreadPoolTaskExecutor) that exposes theExecutorconfiguration parameters as bean properties. There is rarely a need to useConcurrentTaskExecutordirectly. However, if theThreadPoolTaskExecutoris not flexible enough for your needs,ConcurrentTaskExecutoris an alternative. -
ThreadPoolTaskExecutor: This implementation is most commonly used. It exposes bean properties for configuring ajava.util.concurrent.ThreadPoolExecutorand wraps it in aTaskExecutor. If you need to adapt to a different kind ofjava.util.concurrent.Executor, we recommend that you use aConcurrentTaskExecutorinstead. -
DefaultManagedTaskExecutor: This implementation uses a JNDI-obtainedManagedExecutorServicein a JSR-236 compatible runtime environment (such as a Jakarta EE application server), replacing a CommonJ WorkManager for that purpose.
Spring’s TaskExecutor implementations are used as simple JavaBeans. In the following example,
we define a bean that uses the ThreadPoolTaskExecutor to asynchronously print
out a set of messages:
import org.springframework.core.task.TaskExecutor;
public class TaskExecutorExample {
private class MessagePrinterTask implements Runnable {
private String message;
public MessagePrinterTask(String message) {
this.message = message;
}
public void run() {
System.out.println(message);
}
}
private TaskExecutor taskExecutor;
public TaskExecutorExample(TaskExecutor taskExecutor) {
this.taskExecutor = taskExecutor;
}
public void printMessages() {
for(int i = 0; i < 25; i++) {
taskExecutor.execute(new MessagePrinterTask("Message" + i));
}
}
}As you can see, rather than retrieving a thread from the pool and executing it yourself,
you add your Runnable to the queue. Then the TaskExecutor uses its internal rules to
decide when the task gets run.
To configure the rules that the TaskExecutor uses, we expose simple bean properties:
<bean id="taskExecutor" class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor">
<property name="corePoolSize" value="5"/>
<property name="maxPoolSize" value="10"/>
<property name="queueCapacity" value="25"/>
</bean>
<bean id="taskExecutorExample" class="TaskExecutorExample">
<constructor-arg ref="taskExecutor"/>
</bean>In addition to the TaskExecutor abstraction, Spring 3.0 introduced a TaskScheduler
with a variety of methods for scheduling tasks to run at some point in the future.
The following listing shows the TaskScheduler interface definition:
public interface TaskScheduler {
ScheduledFuture schedule(Runnable task, Trigger trigger);
ScheduledFuture schedule(Runnable task, Instant startTime);
ScheduledFuture schedule(Runnable task, Date startTime);
ScheduledFuture scheduleAtFixedRate(Runnable task, Instant startTime, Duration period);
ScheduledFuture scheduleAtFixedRate(Runnable task, Date startTime, long period);
ScheduledFuture scheduleAtFixedRate(Runnable task, Duration period);
ScheduledFuture scheduleAtFixedRate(Runnable task, long period);
ScheduledFuture scheduleWithFixedDelay(Runnable task, Instant startTime, Duration delay);
ScheduledFuture scheduleWithFixedDelay(Runnable task, Date startTime, long delay);
ScheduledFuture scheduleWithFixedDelay(Runnable task, Duration delay);
ScheduledFuture scheduleWithFixedDelay(Runnable task, long delay);
}The simplest method is the one named schedule that takes only a Runnable and a Date.
That causes the task to run once after the specified time. All of the other methods
are capable of scheduling tasks to run repeatedly. The fixed-rate and fixed-delay
methods are for simple, periodic execution, but the method that accepts a Trigger is
much more flexible.
The Trigger interface is essentially inspired by JSR-236 which, as of Spring 3.0,
was not yet officially implemented. The basic idea of the Trigger is that execution
times may be determined based on past execution outcomes or even arbitrary conditions.
If these determinations do take into account the outcome of the preceding execution,
that information is available within a TriggerContext. The Trigger interface itself
is quite simple, as the following listing shows:
public interface Trigger {
Date nextExecutionTime(TriggerContext triggerContext);
}The TriggerContext is the most important part. It encapsulates all of
the relevant data and is open for extension in the future, if necessary. The
TriggerContext is an interface (a SimpleTriggerContext implementation is used by
default). The following listing shows the available methods for Trigger implementations.
public interface TriggerContext {
Date lastScheduledExecutionTime();
Date lastActualExecutionTime();
Date lastCompletionTime();
}Spring provides two implementations of the Trigger interface. The most interesting one
is the CronTrigger. It enables the scheduling of tasks based on
cron expressions.
For example, the following task is scheduled to run 15 minutes past each hour but only
during the 9-to-5 “business hours” on weekdays:
scheduler.schedule(task, new CronTrigger("0 15 9-17 * * MON-FRI"));The other implementation is a PeriodicTrigger that accepts a fixed
period, an optional initial delay value, and a boolean to indicate whether the period
should be interpreted as a fixed-rate or a fixed-delay. Since the TaskScheduler
interface already defines methods for scheduling tasks at a fixed rate or with a
fixed delay, those methods should be used directly whenever possible. The value of the
PeriodicTrigger implementation is that you can use it within components that rely on
the Trigger abstraction. For example, it may be convenient to allow periodic triggers,
cron-based triggers, and even custom trigger implementations to be used interchangeably.
Such a component could take advantage of dependency injection so that you can configure such Triggers
externally and, therefore, easily modify or extend them.
As with Spring’s TaskExecutor abstraction, the primary benefit of the TaskScheduler
arrangement is that an application’s scheduling needs are decoupled from the deployment
environment. This abstraction level is particularly relevant when deploying to an
application server environment where threads should not be created directly by the
application itself. For such scenarios, Spring provides a TimerManagerTaskScheduler
that delegates to a CommonJ TimerManager on WebLogic or WebSphere as well as a more recent
DefaultManagedTaskScheduler that delegates to a JSR-236 ManagedScheduledExecutorService
in a Jakarta EE environment. Both are typically configured with a JNDI lookup.
Whenever external thread management is not a requirement, a simpler alternative is
a local ScheduledExecutorService setup within the application, which can be adapted
through Spring’s ConcurrentTaskScheduler. As a convenience, Spring also provides a
ThreadPoolTaskScheduler, which internally delegates to a ScheduledExecutorService
to provide common bean-style configuration along the lines of ThreadPoolTaskExecutor.
These variants work perfectly fine for locally embedded thread pool setups in lenient
application server environments, as well — in particular on Tomcat and Jetty.
Spring provides annotation support for both task scheduling and asynchronous method execution.
To enable support for @Scheduled and @Async annotations, you can add @EnableScheduling and
@EnableAsync to one of your @Configuration classes, as the following example shows:
@Configuration
@EnableAsync
@EnableScheduling
public class AppConfig {
}You can pick and choose the relevant annotations for your application. For example,
if you need only support for @Scheduled, you can omit @EnableAsync. For more
fine-grained control, you can additionally implement the SchedulingConfigurer
interface, the AsyncConfigurer interface, or both. See the
{api-spring-framework}/scheduling/annotation/SchedulingConfigurer.html[SchedulingConfigurer]
and {api-spring-framework}/scheduling/annotation/AsyncConfigurer.html[AsyncConfigurer]
javadoc for full details.
If you prefer XML configuration, you can use the <task:annotation-driven> element,
as the following example shows:
<task:annotation-driven executor="myExecutor" scheduler="myScheduler"/>
<task:executor id="myExecutor" pool-size="5"/>
<task:scheduler id="myScheduler" pool-size="10"/>Note that, with the preceding XML, an executor reference is provided for handling those
tasks that correspond to methods with the @Async annotation, and the scheduler
reference is provided for managing those methods annotated with @Scheduled.
|
Note
|
The default advice mode for processing @Async annotations is proxy which allows
for interception of calls through the proxy only. Local calls within the same class
cannot get intercepted that way. For a more advanced mode of interception, consider
switching to aspectj mode in combination with compile-time or load-time weaving.
|
You can add the @Scheduled annotation to a method, along with trigger metadata. For
example, the following method is invoked every five seconds (5000 milliseconds) with a
fixed delay, meaning that the period is measured from the completion time of each
preceding invocation.
@Scheduled(fixedDelay = 5000)
public void doSomething() {
// something that should run periodically
}|
Note
|
By default, milliseconds will be used as the time unit for fixed delay, fixed rate, and
initial delay values. If you would like to use a different time unit such as seconds or
minutes, you can configure this via the For example, the previous example can also be written as follows. @Scheduled(fixedDelay = 5, timeUnit = TimeUnit.SECONDS)
public void doSomething() {
// something that should run periodically
} |
If you need a fixed-rate execution, you can use the fixedRate attribute within the
annotation. The following method is invoked every five seconds (measured between the
successive start times of each invocation).
@Scheduled(fixedRate = 5, timeUnit = TimeUnit.SECONDS)
public void doSomething() {
// something that should run periodically
}For fixed-delay and fixed-rate tasks, you can specify an initial delay by indicating the
amount of time to wait before the first execution of the method, as the following
fixedRate example shows.
@Scheduled(initialDelay = 1000, fixedRate = 5000)
public void doSomething() {
// something that should run periodically
}If simple periodic scheduling is not expressive enough, you can provide a cron expression. The following example runs only on weekdays:
@Scheduled(cron="*/5 * * * * MON-FRI")
public void doSomething() {
// something that should run on weekdays only
}|
Tip
|
You can also use the zone attribute to specify the time zone in which the cron
expression is resolved.
|
Notice that the methods to be scheduled must have void returns and must not accept any arguments. If the method needs to interact with other objects from the application context, those would typically have been provided through dependency injection.
|
Note
|
As of Spring Framework 4.3, Make sure that you are not initializing multiple instances of the same |
You can provide the @Async annotation on a method so that invocation of that method
occurs asynchronously. In other words, the caller returns immediately upon
invocation, while the actual execution of the method occurs in a task that has been
submitted to a Spring TaskExecutor. In the simplest case, you can apply the annotation
to a method that returns void, as the following example shows:
@Async
void doSomething() {
// this will be run asynchronously
}Unlike the methods annotated with the @Scheduled annotation, these methods can expect
arguments, because they are invoked in the “normal” way by callers at runtime rather
than from a scheduled task being managed by the container. For example, the following code is
a legitimate application of the @Async annotation:
@Async
void doSomething(String s) {
// this will be run asynchronously
}Even methods that return a value can be invoked asynchronously. However, such methods
are required to have a Future-typed return value. This still provides the benefit of
asynchronous execution so that the caller can perform other tasks prior to calling
get() on that Future. The following example shows how to use @Async on a method
that returns a value:
@Async
Future<String> returnSomething(int i) {
// this will be run asynchronously
}|
Tip
|
@Async methods may not only declare a regular java.util.concurrent.Future return type
but also Spring’s org.springframework.util.concurrent.ListenableFuture or, as of Spring
4.2, JDK 8’s java.util.concurrent.CompletableFuture, for richer interaction with the
asynchronous task and for immediate composition with further processing steps.
|
You can not use @Async in conjunction with lifecycle callbacks such as
@PostConstruct. To asynchronously initialize Spring beans, you currently have to use
a separate initializing Spring bean that then invokes the @Async annotated method on the
target, as the following example shows:
public class SampleBeanImpl implements SampleBean {
@Async
void doSomething() {
// ...
}
}
public class SampleBeanInitializer {
private final SampleBean bean;
public SampleBeanInitializer(SampleBean bean) {
this.bean = bean;
}
@PostConstruct
public void initialize() {
bean.doSomething();
}
}|
Note
|
There is no direct XML equivalent for @Async, since such methods should be designed
for asynchronous execution in the first place, not externally re-declared to be asynchronous.
However, you can manually set up Spring’s AsyncExecutionInterceptor with Spring AOP,
in combination with a custom pointcut.
|
By default, when specifying @Async on a method, the executor that is used is the
one configured when enabling async support,
i.e. the “annotation-driven” element if you are using XML or your AsyncConfigurer
implementation, if any. However, you can use the value attribute of the @Async
annotation when you need to indicate that an executor other than the default should be
used when executing a given method. The following example shows how to do so:
@Async("otherExecutor")
void doSomething(String s) {
// this will be run asynchronously by "otherExecutor"
}In this case, "otherExecutor" can be the name of any Executor bean in the Spring
container, or it may be the name of a qualifier associated with any Executor (for example, as
specified with the <qualifier> element or Spring’s @Qualifier annotation).
When an @Async method has a Future-typed return value, it is easy to manage
an exception that was thrown during the method execution, as this exception is
thrown when calling get on the Future result. With a void return type,
however, the exception is uncaught and cannot be transmitted. You can provide an
AsyncUncaughtExceptionHandler to handle such exceptions. The following example shows
how to do so:
public class MyAsyncUncaughtExceptionHandler implements AsyncUncaughtExceptionHandler {
@Override
public void handleUncaughtException(Throwable ex, Method method, Object... params) {
// handle exception
}
}By default, the exception is merely logged. You can define a custom AsyncUncaughtExceptionHandler
by using AsyncConfigurer or the <task:annotation-driven/> XML element.
As of version 3.0, Spring includes an XML namespace for configuring TaskExecutor and
TaskScheduler instances. It also provides a convenient way to configure tasks to be
scheduled with a trigger.
The following element creates a ThreadPoolTaskScheduler instance with the
specified thread pool size:
<task:scheduler id="scheduler" pool-size="10"/>The value provided for the id attribute is used as the prefix for thread names
within the pool. The scheduler element is relatively straightforward. If you do not
provide a pool-size attribute, the default thread pool has only a single thread.
There are no other configuration options for the scheduler.
The following creates a ThreadPoolTaskExecutor instance:
<task:executor id="executor" pool-size="10"/>As with the scheduler shown in the previous section,
the value provided for the id attribute is used as the prefix for thread names within
the pool. As far as the pool size is concerned, the executor element supports more
configuration options than the scheduler element. For one thing, the thread pool for
a ThreadPoolTaskExecutor is itself more configurable. Rather than only a single size,
an executor’s thread pool can have different values for the core and the max size.
If you provide a single value, the executor has a fixed-size thread pool (the core and
max sizes are the same). However, the executor element’s pool-size attribute also
accepts a range in the form of min-max. The following example sets a minimum value of
5 and a maximum value of 25:
<task:executor
id="executorWithPoolSizeRange"
pool-size="5-25"
queue-capacity="100"/>In the preceding configuration, a queue-capacity value has also been provided.
The configuration of the thread pool should also be considered in light of the
executor’s queue capacity. For the full description of the relationship between pool
size and queue capacity, see the documentation for
ThreadPoolExecutor.
The main idea is that, when a task is submitted, the executor first tries to use a
free thread if the number of active threads is currently less than the core size.
If the core size has been reached, the task is added to the queue, as long as its
capacity has not yet been reached. Only then, if the queue’s capacity has been
reached, does the executor create a new thread beyond the core size. If the max size
has also been reached, then the executor rejects the task.
By default, the queue is unbounded, but this is rarely the desired configuration,
because it can lead to OutOfMemoryErrors if enough tasks are added to that queue while
all pool threads are busy. Furthermore, if the queue is unbounded, the max size has
no effect at all. Since the executor always tries the queue before creating a new
thread beyond the core size, a queue must have a finite capacity for the thread pool to
grow beyond the core size (this is why a fixed-size pool is the only sensible case
when using an unbounded queue).
Consider the case, as mentioned above, when a task is rejected. By default, when a
task is rejected, a thread pool executor throws a TaskRejectedException. However,
the rejection policy is actually configurable. The exception is thrown when using
the default rejection policy, which is the AbortPolicy implementation.
For applications where some tasks can be skipped under heavy load, you can instead
configure either DiscardPolicy or DiscardOldestPolicy. Another option that works
well for applications that need to throttle the submitted tasks under heavy load is
the CallerRunsPolicy. Instead of throwing an exception or discarding tasks,
that policy forces the thread that is calling the submit method to run the task itself.
The idea is that such a caller is busy while running that task and not able to submit
other tasks immediately. Therefore, it provides a simple way to throttle the incoming
load while maintaining the limits of the thread pool and queue. Typically, this allows
the executor to “catch up” on the tasks it is handling and thereby frees up some
capacity on the queue, in the pool, or both. You can choose any of these options from an
enumeration of values available for the rejection-policy attribute on the executor
element.
The following example shows an executor element with a number of attributes to specify
various behaviors:
<task:executor
id="executorWithCallerRunsPolicy"
pool-size="5-25"
queue-capacity="100"
rejection-policy="CALLER_RUNS"/>Finally, the keep-alive setting determines the time limit (in seconds) for which threads
may remain idle before being stopped. If there are more than the core number of threads
currently in the pool, after waiting this amount of time without processing a task, excess
threads get stopped. A time value of zero causes excess threads to stop
immediately after executing a task without remaining follow-up work in the task queue.
The following example sets the keep-alive value to two minutes:
<task:executor
id="executorWithKeepAlive"
pool-size="5-25"
keep-alive="120"/>The most powerful feature of Spring’s task namespace is the support for configuring
tasks to be scheduled within a Spring Application Context. This follows an approach
similar to other “method-invokers” in Spring, such as that provided by the JMS namespace
for configuring message-driven POJOs. Basically, a ref attribute can point to any
Spring-managed object, and the method attribute provides the name of a method to be
invoked on that object. The following listing shows a simple example:
<task:scheduled-tasks scheduler="myScheduler">
<task:scheduled ref="beanA" method="methodA" fixed-delay="5000"/>
</task:scheduled-tasks>
<task:scheduler id="myScheduler" pool-size="10"/>The scheduler is referenced by the outer element, and each individual
task includes the configuration of its trigger metadata. In the preceding example, that
metadata defines a periodic trigger with a fixed delay indicating the number of
milliseconds to wait after each task execution has completed. Another option is
fixed-rate, indicating how often the method should be run regardless of how long
any previous execution takes. Additionally, for both fixed-delay and fixed-rate tasks, you can specify an
'initial-delay' parameter, indicating the number of milliseconds to wait
before the first execution of the method. For more control, you can instead provide a cron attribute
to provide a cron expression.
The following example shows these other options:
<task:scheduled-tasks scheduler="myScheduler">
<task:scheduled ref="beanA" method="methodA" fixed-delay="5000" initial-delay="1000"/>
<task:scheduled ref="beanB" method="methodB" fixed-rate="5000"/>
<task:scheduled ref="beanC" method="methodC" cron="*/5 * * * * MON-FRI"/>
</task:scheduled-tasks>
<task:scheduler id="myScheduler" pool-size="10"/>All Spring cron expressions have to conform to the same format, whether you are using them in
@Scheduled annotations,
task:scheduled-tasks elements,
or someplace else.
A well-formed cron expression, such as * * * * * *, consists of six space-separated time and date
fields, each with its own range of valid values:
┌───────────── second (0-59) │ ┌───────────── minute (0 - 59) │ │ ┌───────────── hour (0 - 23) │ │ │ ┌───────────── day of the month (1 - 31) │ │ │ │ ┌───────────── month (1 - 12) (or JAN-DEC) │ │ │ │ │ ┌───────────── day of the week (0 - 7) │ │ │ │ │ │ (0 or 7 is Sunday, or MON-SUN) │ │ │ │ │ │ * * * * * *
There are some rules that apply:
-
A field may be an asterisk (
*), which always stands for “first-last”. For the day-of-the-month or day-of-the-week fields, a question mark (?) may be used instead of an asterisk. -
Commas (
,) are used to separate items of a list. -
Two numbers separated with a hyphen (
-) express a range of numbers. The specified range is inclusive. -
Following a range (or
*) with/specifies the interval of the number’s value through the range. -
English names can also be used for the day-of-month and day-of-week fields. Use the first three letters of the particular day or month (case does not matter).
-
The day-of-month and day-of-week fields can contain a
Lcharacter, which has a different meaning-
In the day-of-month field,
Lstands for the last day of the month. If followed by a negative offset (that is,L-n), it meansnth-to-last day of the month. -
In the day-of-week field,
Lstands for the last day of the week. If prefixed by a number or three-letter name (dLorDDDL), it means the last day of week (dorDDD) in the month.
-
-
The day-of-month field can be
nW, which stands for the nearest weekday to day of the monthn. Ifnfalls on Saturday, this yields the Friday before it. Ifnfalls on Sunday, this yields the Monday after, which also happens ifnis1and falls on a Saturday (that is:1Wstands for the first weekday of the month). -
If the day-of-month field is
LW, it means the last weekday of the month. -
The day-of-week field can be
d#n(orDDD#n), which stands for thenth day of weekd(orDDD) in the month.
Here are some examples:
| Cron Expression | Meaning |
|---|---|
|
top of every hour of every day |
|
every ten seconds |
|
8, 9 and 10 o’clock of every day |
|
6:00 AM and 7:00 PM every day |
|
8:00, 8:30, 9:00, 9:30, 10:00 and 10:30 every day |
|
on the hour nine-to-five weekdays |
|
every Christmas Day at midnight |
|
last day of the month at midnight |
|
third-to-last day of the month at midnight |
|
last Friday of the month at midnight |
|
last Thursday of the month at midnight |
|
first weekday of the month at midnight |
|
last weekday of the month at midnight |
|
the second Friday in the month at midnight |
|
the first Monday in the month at midnight |
Expressions such as 0 0 * * * * are hard for humans to parse and are, therefore, hard to fix in case of bugs.
To improve readability, Spring supports the following macros, which represent commonly used sequences.
You can use these macros instead of the six-digit value, thus: @Scheduled(cron = "@hourly").
| Macro | Meaning |
|---|---|
|
once a year ( |
|
once a month ( |
|
once a week ( |
|
once a day ( |
|
once an hour, ( |
Quartz uses Trigger, Job, and JobDetail objects to realize scheduling of all kinds
of jobs. For the basic concepts behind Quartz, see
https://www.quartz-scheduler.org/. For convenience purposes, Spring offers a couple of
classes that simplify using Quartz within Spring-based applications.
Quartz JobDetail objects contain all the information needed to run a job. Spring provides a
JobDetailFactoryBean, which provides bean-style properties for XML configuration purposes.
Consider the following example:
<bean name="exampleJob" class="org.springframework.scheduling.quartz.JobDetailFactoryBean">
<property name="jobClass" value="example.ExampleJob"/>
<property name="jobDataAsMap">
<map>
<entry key="timeout" value="5"/>
</map>
</property>
</bean>The job detail configuration has all the information it needs to run the job (ExampleJob).
The timeout is specified in the job data map. The job data map is available through the
JobExecutionContext (passed to you at execution time), but the JobDetail also gets
its properties from the job data mapped to properties of the job instance. So, in the following example,
the ExampleJob contains a bean property named timeout, and the JobDetail
has it applied automatically:
package example;
public class ExampleJob extends QuartzJobBean {
private int timeout;
/**
* Setter called after the ExampleJob is instantiated
* with the value from the JobDetailFactoryBean (5)
*/
public void setTimeout(int timeout) {
this.timeout = timeout;
}
protected void executeInternal(JobExecutionContext ctx) throws JobExecutionException {
// do the actual work
}
}All additional properties from the job data map are available to you as well.
|
Note
|
By using the name and group properties, you can modify the name and the group
of the job, respectively. By default, the name of the job matches the bean name
of the JobDetailFactoryBean (exampleJob in the preceding example above).
|
Often you merely need to invoke a method on a specific object. By using the
MethodInvokingJobDetailFactoryBean, you can do exactly this, as the following example shows:
<bean id="jobDetail" class="org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean">
<property name="targetObject" ref="exampleBusinessObject"/>
<property name="targetMethod" value="doIt"/>
</bean>The preceding example results in the doIt method being called on the
exampleBusinessObject method, as the following example shows:
public class ExampleBusinessObject {
// properties and collaborators
public void doIt() {
// do the actual work
}
}<bean id="exampleBusinessObject" class="examples.ExampleBusinessObject"/>By using the MethodInvokingJobDetailFactoryBean, you need not create one-line jobs
that merely invoke a method. You need only create the actual business object and
wire up the detail object.
By default, Quartz Jobs are stateless, resulting in the possibility of jobs interfering
with each other. If you specify two triggers for the same JobDetail, it is
possible that, before the first job has finished, the second one starts. If
JobDetail classes implement the Stateful interface, this does not happen. The second
job does not start before the first one has finished. To make jobs resulting from the
MethodInvokingJobDetailFactoryBean be non-concurrent, set the concurrent flag to
false, as the following example shows:
<bean id="jobDetail" class="org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean">
<property name="targetObject" ref="exampleBusinessObject"/>
<property name="targetMethod" value="doIt"/>
<property name="concurrent" value="false"/>
</bean>|
Note
|
By default, jobs will run in a concurrent fashion. |
We have created job details and jobs. We have also reviewed the convenience bean that lets
you invoke a method on a specific object. Of course, we still need to schedule the
jobs themselves. This is done by using triggers and a SchedulerFactoryBean. Several
triggers are available within Quartz, and Spring offers two Quartz FactoryBean
implementations with convenient defaults: CronTriggerFactoryBean and
SimpleTriggerFactoryBean.
Triggers need to be scheduled. Spring offers a SchedulerFactoryBean that exposes
triggers to be set as properties. SchedulerFactoryBean schedules the actual jobs with
those triggers.
The following listing uses both a SimpleTriggerFactoryBean and a CronTriggerFactoryBean:
<bean id="simpleTrigger" class="org.springframework.scheduling.quartz.SimpleTriggerFactoryBean">
<!-- see the example of method invoking job above -->
<property name="jobDetail" ref="jobDetail"/>
<!-- 10 seconds -->
<property name="startDelay" value="10000"/>
<!-- repeat every 50 seconds -->
<property name="repeatInterval" value="50000"/>
</bean>
<bean id="cronTrigger" class="org.springframework.scheduling.quartz.CronTriggerFactoryBean">
<property name="jobDetail" ref="exampleJob"/>
<!-- run every morning at 6 AM -->
<property name="cronExpression" value="0 0 6 * * ?"/>
</bean>The preceding example sets up two triggers, one running every 50 seconds with a starting delay of 10
seconds and one running every morning at 6 AM. To finalize everything, we need to set up the
SchedulerFactoryBean, as the following example shows:
<bean class="org.springframework.scheduling.quartz.SchedulerFactoryBean">
<property name="triggers">
<list>
<ref bean="cronTrigger"/>
<ref bean="simpleTrigger"/>
</list>
</property>
</bean>More properties are available for the SchedulerFactoryBean, such as the calendars used by the
job details, properties to customize Quartz with, and a Spring-provided JDBC DataSource. See
the {api-spring-framework}/scheduling/quartz/SchedulerFactoryBean.html[SchedulerFactoryBean]
javadoc for more information.
|
Note
|
SchedulerFactoryBean also recognizes a quartz.properties file in the classpath,
based on Quartz property keys, as with regular Quartz configuration. Please note that many
SchedulerFactoryBean settings interact with common Quartz settings in the properties file;
it is therefore not recommended to specify values at both levels. For example, do not set
an "org.quartz.jobStore.class" property if you mean to rely on a Spring-provided DataSource,
or specify an org.springframework.scheduling.quartz.LocalDataSourceJobStore variant which
is a full-fledged replacement for the standard org.quartz.impl.jdbcjobstore.JobStoreTX.
|
Since version 3.1, the Spring Framework provides support for transparently adding caching to an existing Spring application. Similar to the transaction support, the caching abstraction allows consistent use of various caching solutions with minimal impact on the code.
In Spring Framework 4.1, the cache abstraction was significantly extended with support for JSR-107 annotations and more customization options.
The terms, “buffer” and “cache,” tend to be used interchangeably. Note, however, that they represent different things. Traditionally, a buffer is used as an intermediate temporary store for data between a fast and a slow entity. As one party would have to wait for the other (which affects performance), the buffer alleviates this by allowing entire blocks of data to move at once rather than in small chunks. The data is written and read only once from the buffer. Furthermore, the buffers are visible to at least one party that is aware of it.
A cache, on the other hand, is, by definition, hidden, and neither party is aware that caching occurs. It also improves performance but does so by letting the same data be read multiple times in a fast fashion.
You can find a further explanation of the differences between a buffer and a cache here.
At its core, the cache abstraction applies caching to Java methods, thus reducing the number of executions based on the information available in the cache. That is, each time a targeted method is invoked, the abstraction applies a caching behavior that checks whether the method has been already invoked for the given arguments. If it has been invoked, the cached result is returned without having to invoke the actual method. If the method has not been invoked, then it is invoked, and the result is cached and returned to the user so that, the next time the method is invoked, the cached result is returned. This way, expensive methods (whether CPU- or IO-bound) can be invoked only once for a given set of parameters and the result reused without having to actually invoke the method again. The caching logic is applied transparently without any interference to the invoker.
|
Important
|
This approach works only for methods that are guaranteed to return the same output (result) for a given input (or arguments) no matter how many times they are invoked. |
The caching abstraction provides other cache-related operations, such as the ability to update the content of the cache or to remove one or all entries. These are useful if the cache deals with data that can change during the course of the application.
As with other services in the Spring Framework, the caching service is an abstraction
(not a cache implementation) and requires the use of actual storage to store the cache data — that is, the abstraction frees you from having to write the caching logic but does not
provide the actual data store. This abstraction is materialized by the
org.springframework.cache.Cache and org.springframework.cache.CacheManager interfaces.
Spring provides a few implementations of that abstraction:
JDK java.util.concurrent.ConcurrentMap based caches, Gemfire cache,
Caffeine, and JSR-107 compliant caches (such
as Ehcache 3.x). See Plugging-in Different Back-end Caches for more information on plugging in other cache
stores and providers.
|
Important
|
The caching abstraction has no special handling for multi-threaded and multi-process environments, as such features are handled by the cache implementation. |
If you have a multi-process environment (that is, an application deployed on several nodes), you need to configure your cache provider accordingly. Depending on your use cases, a copy of the same data on several nodes can be enough. However, if you change the data during the course of the application, you may need to enable other propagation mechanisms.
Caching a particular item is a direct equivalent of the typical get-if-not-found-then-proceed-and-put-eventually code blocks found with programmatic cache interaction. No locks are applied, and several threads may try to load the same item concurrently. The same applies to eviction. If several threads are trying to update or evict data concurrently, you may use stale data. Certain cache providers offer advanced features in that area. See the documentation of your cache provider for more details.
To use the cache abstraction, you need to take care of two aspects:
-
Caching declaration: Identify the methods that need to be cached and their policies.
-
Cache configuration: The backing cache where the data is stored and from which it is read.
For caching declaration, Spring’s caching abstraction provides a set of Java annotations:
-
@Cacheable: Triggers cache population. -
@CacheEvict: Triggers cache eviction. -
@CachePut: Updates the cache without interfering with the method execution. -
@Caching: Regroups multiple cache operations to be applied on a method. -
@CacheConfig: Shares some common cache-related settings at class-level.
As the name implies, you can use @Cacheable to demarcate methods that are cacheable — that is, methods for which the result is stored in the cache so that, on subsequent
invocations (with the same arguments), the value in the cache is returned without
having to actually invoke the method. In its simplest form, the annotation declaration
requires the name of the cache associated with the annotated method, as the following
example shows:
@Cacheable("books")
public Book findBook(ISBN isbn) {...}In the preceding snippet, the findBook method is associated with the cache named books.
Each time the method is called, the cache is checked to see whether the invocation has
already been run and does not have to be repeated. While in most cases, only one
cache is declared, the annotation lets multiple names be specified so that more than one
cache is being used. In this case, each of the caches is checked before invoking the
method — if at least one cache is hit, the associated value is returned.
|
Note
|
All the other caches that do not contain the value are also updated, even though the cached method was not actually invoked. |
The following example uses @Cacheable on the findBook method with multiple caches:
@Cacheable({"books", "isbns"})
public Book findBook(ISBN isbn) {...}Since caches are essentially key-value stores, each invocation of a cached method
needs to be translated into a suitable key for cache access. The caching abstraction
uses a simple KeyGenerator based on the following algorithm:
-
If no params are given, return
SimpleKey.EMPTY. -
If only one param is given, return that instance.
-
If more than one param is given, return a
SimpleKeythat contains all parameters.
This approach works well for most use-cases, as long as parameters have natural keys
and implement valid hashCode() and equals() methods. If that is not the case,
you need to change the strategy.
To provide a different default key generator, you need to implement the
org.springframework.cache.interceptor.KeyGenerator interface.
|
Note
|
The default key generation strategy changed with the release of Spring 4.0. Earlier
versions of Spring used a key generation strategy that, for multiple key parameters,
considered only the If you want to keep using the previous key strategy, you can configure the deprecated
|
Since caching is generic, the target methods are quite likely to have various signatures that cannot be readily mapped on top of the cache structure. This tends to become obvious when the target method has multiple arguments out of which only some are suitable for caching (while the rest are used only by the method logic). Consider the following example:
@Cacheable("books")
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)At first glance, while the two boolean arguments influence the way the book is found,
they are no use for the cache. Furthermore, what if only one of the two is important
while the other is not?
For such cases, the @Cacheable annotation lets you specify how the key is generated
through its key attribute. You can use SpEL to pick the
arguments of interest (or their nested properties), perform operations, or even
invoke arbitrary methods without having to write any code or implement any interface.
This is the recommended approach over the
default generator, since methods tend to be
quite different in signatures as the code base grows. While the default strategy might
work for some methods, it rarely works for all methods.
The following examples use various SpEL declarations (if you are not familiar with SpEL, do yourself a favor and read Spring Expression Language):
@Cacheable(cacheNames="books", key="#isbn")
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)
@Cacheable(cacheNames="books", key="#isbn.rawNumber")
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)
@Cacheable(cacheNames="books", key="T(someType).hash(#isbn)")
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)The preceding snippets show how easy it is to select a certain argument, one of its properties, or even an arbitrary (static) method.
If the algorithm responsible for generating the key is too specific or if it needs
to be shared, you can define a custom keyGenerator on the operation. To do so,
specify the name of the KeyGenerator bean implementation to use, as the following
example shows:
@Cacheable(cacheNames="books", keyGenerator="myKeyGenerator")
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)|
Note
|
The key and keyGenerator parameters are mutually exclusive and an operation
that specifies both results in an exception.
|
The caching abstraction uses a simple CacheResolver that
retrieves the caches defined at the operation level by using the configured
CacheManager.
To provide a different default cache resolver, you need to implement the
org.springframework.cache.interceptor.CacheResolver interface.
The default cache resolution fits well for applications that work with a
single CacheManager and have no complex cache resolution requirements.
For applications that work with several cache managers, you can set the
cacheManager to use for each operation, as the following example shows:
@Cacheable(cacheNames="books", cacheManager="anotherCacheManager") (1)
public Book findBook(ISBN isbn) {...}-
Specifying
anotherCacheManager.
You can also replace the CacheResolver entirely in a fashion similar to that of
replacing key generation. The resolution is
requested for every cache operation, letting the implementation actually resolve
the caches to use based on runtime arguments. The following example shows how to
specify a CacheResolver:
@Cacheable(cacheResolver="runtimeCacheResolver") (1)
public Book findBook(ISBN isbn) {...}-
Specifying the
CacheResolver.
|
Note
|
Since Spring 4.1, the Similarly to |
In a multi-threaded environment, certain operations might be concurrently invoked for the same argument (typically on startup). By default, the cache abstraction does not lock anything, and the same value may be computed several times, defeating the purpose of caching.
For those particular cases, you can use the sync attribute to instruct the underlying
cache provider to lock the cache entry while the value is being computed. As a result,
only one thread is busy computing the value, while the others are blocked until the entry
is updated in the cache. The following example shows how to use the sync attribute:
@Cacheable(cacheNames="foos", sync=true) (1)
public Foo executeExpensiveOperation(String id) {...}-
Using the
syncattribute.
|
Note
|
This is an optional feature, and your favorite cache library may not support it.
All CacheManager implementations provided by the core framework support it. See the
documentation of your cache provider for more details.
|
Sometimes, a method might not be suitable for caching all the time (for example, it might
depend on the given arguments). The cache annotations support such use cases through the
condition parameter, which takes a SpEL expression that is evaluated to either true
or false. If true, the method is cached. If not, it behaves as if the method is not
cached (that is, the method is invoked every time no matter what values are in the cache
or what arguments are used). For example, the following method is cached only if the
argument name has a length shorter than 32:
@Cacheable(cacheNames="book", condition="#name.length() < 32") (1)
public Book findBook(String name)-
Setting a condition on
@Cacheable.
In addition to the condition parameter, you can use the unless parameter to veto the
adding of a value to the cache. Unlike condition, unless expressions are evaluated
after the method has been invoked. To expand on the previous example, perhaps we only
want to cache paperback books, as the following example does:
@Cacheable(cacheNames="book", condition="#name.length() < 32", unless="#result.hardback") (1)
public Book findBook(String name)-
Using the
unlessattribute to block hardbacks.
The cache abstraction supports java.util.Optional return types. If an Optional value
is present, it will be stored in the associated cache. If an Optional value is not
present, null will be stored in the associated cache. #result always refers to the
business entity and never a supported wrapper, so the previous example can be rewritten
as follows:
@Cacheable(cacheNames="book", condition="#name.length() < 32", unless="#result?.hardback")
public Optional<Book> findBook(String name)Note that #result still refers to Book and not Optional<Book>. Since it might be
null, we use SpEL’s safe navigation operator.
Each SpEL expression evaluates against a dedicated context.
In addition to the built-in parameters, the framework provides dedicated caching-related
metadata, such as the argument names. The following table describes the items made
available to the context so that you can use them for key and conditional computations:
| Name | Location | Description | Example |
|---|---|---|---|
|
Root object |
The name of the method being invoked |
|
|
Root object |
The method being invoked |
|
|
Root object |
The target object being invoked |
|
|
Root object |
The class of the target being invoked |
|
|
Root object |
The arguments (as array) used for invoking the target |
|
|
Root object |
Collection of caches against which the current method is run |
|
Argument name |
Evaluation context |
Name of any of the method arguments. If the names are not available
(perhaps due to having no debug information), the argument names are also available under the |
|
|
Evaluation context |
The result of the method call (the value to be cached). Only available in |
|
When the cache needs to be updated without interfering with the method execution,
you can use the @CachePut annotation. That is, the method is always invoked and its
result is placed into the cache (according to the @CachePut options). It supports
the same options as @Cacheable and should be used for cache population rather than
method flow optimization. The following example uses the @CachePut annotation:
@CachePut(cacheNames="book", key="#isbn")
public Book updateBook(ISBN isbn, BookDescriptor descriptor)|
Important
|
Using @CachePut and @Cacheable annotations on the same method is generally
strongly discouraged because they have different behaviors. While the latter causes the
method invocation to be skipped by using the cache, the former forces the invocation in
order to run a cache update. This leads to unexpected behavior and, with the exception
of specific corner-cases (such as annotations having conditions that exclude them from each
other), such declarations should be avoided. Note also that such conditions should not rely
on the result object (that is, the #result variable), as these are validated up-front to
confirm the exclusion.
|
The cache abstraction allows not just population of a cache store but also eviction.
This process is useful for removing stale or unused data from the cache. As opposed to
@Cacheable, @CacheEvict demarcates methods that perform cache
eviction (that is, methods that act as triggers for removing data from the cache).
Similarly to its sibling, @CacheEvict requires specifying one or more caches
that are affected by the action, allows a custom cache and key resolution or a
condition to be specified, and features an extra parameter
(allEntries) that indicates whether a cache-wide eviction needs to be performed
rather than just an entry eviction (based on the key). The following example evicts
all entries from the books cache:
@CacheEvict(cacheNames="books", allEntries=true) (1)
public void loadBooks(InputStream batch)-
Using the
allEntriesattribute to evict all entries from the cache.
This option comes in handy when an entire cache region needs to be cleared out. Rather than evicting each entry (which would take a long time, since it is inefficient), all the entries are removed in one operation, as the preceding example shows. Note that the framework ignores any key specified in this scenario as it does not apply (the entire cache is evicted, not only one entry).
You can also indicate whether the eviction should occur after (the default) or before
the method is invoked by using the beforeInvocation attribute. The former provides the
same semantics as the rest of the annotations: Once the method completes successfully,
an action (in this case, eviction) on the cache is run. If the method does not
run (as it might be cached) or an exception is thrown, the eviction does not occur.
The latter (beforeInvocation=true) causes the eviction to always occur before the
method is invoked. This is useful in cases where the eviction does not need to be tied
to the method outcome.
Note that void methods can be used with @CacheEvict - as the methods act as a
trigger, the return values are ignored (as they do not interact with the cache). This is
not the case with @Cacheable which adds data to the cache or updates data in the cache
and, thus, requires a result.
Sometimes, multiple annotations of the same type (such as @CacheEvict or
@CachePut) need to be specified — for example, because the condition or the key
expression is different between different caches. @Caching lets multiple nested
@Cacheable, @CachePut, and @CacheEvict annotations be used on the same method.
The following example uses two @CacheEvict annotations:
@Caching(evict = { @CacheEvict("primary"), @CacheEvict(cacheNames="secondary", key="#p0") })
public Book importBooks(String deposit, Date date)So far, we have seen that caching operations offer many customization options and that
you can set these options for each operation. However, some of the customization options
can be tedious to configure if they apply to all operations of the class. For
instance, specifying the name of the cache to use for every cache operation of the
class can be replaced by a single class-level definition. This is where @CacheConfig
comes into play. The following examples uses @CacheConfig to set the name of the cache:
@CacheConfig("books") (1)
public class BookRepositoryImpl implements BookRepository {
@Cacheable
public Book findBook(ISBN isbn) {...}
}-
Using
@CacheConfigto set the name of the cache.
@CacheConfig is a class-level annotation that allows sharing the cache names,
the custom KeyGenerator, the custom CacheManager, and the custom CacheResolver.
Placing this annotation on the class does not turn on any caching operation.
An operation-level customization always overrides a customization set on @CacheConfig.
Therefore, this gives three levels of customizations for each cache operation:
-
Globally configured, available for
CacheManager,KeyGenerator. -
At the class level, using
@CacheConfig. -
At the operation level.
It is important to note that even though declaring the cache annotations does not automatically trigger their actions - like many things in Spring, the feature has to be declaratively enabled (which means if you ever suspect caching is to blame, you can disable it by removing only one configuration line rather than all the annotations in your code).
To enable caching annotations add the annotation @EnableCaching to one of your
@Configuration classes:
@Configuration
@EnableCaching
public class AppConfig {
}Alternatively, for XML configuration you can use the cache:annotation-driven element:
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:cache="http://www.springframework.org/schema/cache"
xsi:schemaLocation="
http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/cache https://www.springframework.org/schema/cache/spring-cache.xsd">
<cache:annotation-driven/>
</beans>Both the cache:annotation-driven element and the @EnableCaching annotation let you
specify various options that influence the way the caching behavior is added to the
application through AOP. The configuration is intentionally similar with that of
@Transactional.
|
Note
|
The default advice mode for processing caching annotations is proxy, which allows
for interception of calls through the proxy only. Local calls within the same class
cannot get intercepted that way. For a more advanced mode of interception, consider
switching to aspectj mode in combination with compile-time or load-time weaving.
|
|
Note
|
For more detail about advanced customizations (using Java configuration) that are
required to implement CachingConfigurer, see the
{api-spring-framework}/cache/annotation/CachingConfigurer.html[javadoc].
|
| XML Attribute | Annotation Attribute | Default | Description |
|---|---|---|---|
|
N/A (see the {api-spring-framework}/cache/annotation/CachingConfigurer.html[ |
|
The name of the cache manager to use. A default |
|
N/A (see the {api-spring-framework}/cache/annotation/CachingConfigurer.html[ |
A |
The bean name of the CacheResolver that is to be used to resolve the backing caches. This attribute is not required and needs to be specified only as an alternative to the 'cache-manager' attribute. |
|
N/A (see the {api-spring-framework}/cache/annotation/CachingConfigurer.html[ |
|
Name of the custom key generator to use. |
|
N/A (see the {api-spring-framework}/cache/annotation/CachingConfigurer.html[ |
|
The name of the custom cache error handler to use. By default, any exception thrown during a cache related operation is thrown back at the client. |
|
|
|
The default mode ( |
|
|
|
Applies to proxy mode only. Controls what type of caching proxies are created for
classes annotated with the |
|
|
Ordered.LOWEST_PRECEDENCE |
Defines the order of the cache advice that is applied to beans annotated with
|
|
Note
|
<cache:annotation-driven/> looks for @Cacheable/@CachePut/@CacheEvict/@Caching
only on beans in the same application context in which it is defined. This means that,
if you put <cache:annotation-driven/> in a WebApplicationContext for a
DispatcherServlet, it checks for beans only in your controllers, not your services.
See the MVC section for more information.
|
When you use proxies, you should apply the cache annotations only to methods with public visibility. If you do annotate protected, private, or package-visible methods with these annotations, no error is raised, but the annotated method does not exhibit the configured caching settings. Consider using AspectJ (see the rest of this section) if you need to annotate non-public methods, as it changes the bytecode itself.
|
Tip
|
Spring recommends that you only annotate concrete classes (and methods of concrete
classes) with the @Cache* annotations, as opposed to annotating interfaces.
You certainly can place an @Cache* annotation on an interface (or an interface
method), but this works only if you use the proxy mode (mode="proxy"). If you use the
weaving-based aspect (mode="aspectj"), the caching settings are not recognized on
interface-level declarations by the weaving infrastructure.
|
|
Note
|
In proxy mode (the default), only external method calls coming in through the
proxy are intercepted. This means that self-invocation (in effect, a method within the
target object that calls another method of the target object) does not lead to actual
caching at runtime even if the invoked method is marked with @Cacheable. Consider
using the aspectj mode in this case. Also, the proxy must be fully initialized to
provide the expected behavior, so you should not rely on this feature in your
initialization code (that is, @PostConstruct).
|
This feature works only with the proxy-based approach but can be enabled with a bit of extra effort by using AspectJ.
The spring-aspects module defines an aspect for the standard annotations only.
If you have defined your own annotations, you also need to define an aspect for
those. Check AnnotationCacheAspect for an example.
The caching abstraction lets you use your own annotations to identify what method
triggers cache population or eviction. This is quite handy as a template mechanism,
as it eliminates the need to duplicate cache annotation declarations, which is
especially useful if the key or condition are specified or if the foreign imports
(org.springframework) are not allowed in your code base. Similarly to the rest
of the stereotype annotations, you can
use @Cacheable, @CachePut, @CacheEvict, and @CacheConfig as
meta-annotations (that is, annotations that
can annotate other annotations). In the following example, we replace a common
@Cacheable declaration with our own custom annotation:
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
@Cacheable(cacheNames="books", key="#isbn")
public @interface SlowService {
}In the preceding example, we have defined our own SlowService annotation,
which itself is annotated with @Cacheable. Now we can replace the following code:
@Cacheable(cacheNames="books", key="#isbn")
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)The following example shows the custom annotation with which we can replace the preceding code:
@SlowService
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)Even though @SlowService is not a Spring annotation, the container automatically picks
up its declaration at runtime and understands its meaning. Note that, as mentioned
earlier, annotation-driven behavior needs to be enabled.
Since version 4.1, Spring’s caching abstraction fully supports the JCache standard
(JSR-107) annotations: @CacheResult, @CachePut, @CacheRemove, and @CacheRemoveAll
as well as the @CacheDefaults, @CacheKey, and @CacheValue companions.
You can use these annotations even without migrating your cache store to JSR-107.
The internal implementation uses Spring’s caching abstraction and provides default
CacheResolver and KeyGenerator implementations that are compliant with the
specification. In other words, if you are already using Spring’s caching abstraction,
you can switch to these standard annotations without changing your cache storage
(or configuration, for that matter).
For those who are familiar with Spring’s caching annotations, the following table describes the main differences between the Spring annotations and their JSR-107 counterparts:
| Spring | JSR-107 | Remark |
|---|---|---|
|
|
Fairly similar. |
|
|
While Spring updates the cache with the result of the method invocation, JCache
requires that it be passed it as an argument that is annotated with |
|
|
Fairly similar. |
|
|
See |
|
|
Lets you configure the same concepts, in a similar fashion. |
JCache has the notion of javax.cache.annotation.CacheResolver, which is identical
to the Spring’s CacheResolver interface, except that JCache supports only a single
cache. By default, a simple implementation retrieves the cache to use based on the
name declared on the annotation. It should be noted that, if no cache name is
specified on the annotation, a default is automatically generated. See the javadoc
of @CacheResult#cacheName() for more information.
CacheResolver instances are retrieved by a CacheResolverFactory. It is possible
to customize the factory for each cache operation, as the following example shows:
@CacheResult(cacheNames="books", cacheResolverFactory=MyCacheResolverFactory.class) (1)
public Book findBook(ISBN isbn)-
Customizing the factory for this operation.
|
Note
|
For all referenced classes, Spring tries to locate a bean with the given type. If more than one match exists, a new instance is created and can use the regular bean lifecycle callbacks, such as dependency injection. |
Keys are generated by a javax.cache.annotation.CacheKeyGenerator that serves the
same purpose as Spring’s KeyGenerator. By default, all method arguments are taken
into account, unless at least one parameter is annotated with @CacheKey. This is
similar to Spring’s custom key generation
declaration. For instance, the following are identical operations, one using
Spring’s abstraction and the other using JCache:
@Cacheable(cacheNames="books", key="#isbn")
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)
@CacheResult(cacheName="books")
public Book findBook(@CacheKey ISBN isbn, boolean checkWarehouse, boolean includeUsed)You can also specify the CacheKeyResolver on the operation, similar to how you can
specify the CacheResolverFactory.
JCache can manage exceptions thrown by annotated methods. This can prevent an update of
the cache, but it can also cache the exception as an indicator of the failure instead of
calling the method again. Assume that InvalidIsbnNotFoundException is thrown if the
structure of the ISBN is invalid. This is a permanent failure (no book could ever be
retrieved with such a parameter). The following caches the exception so that further
calls with the same, invalid, ISBN throw the cached exception directly instead of
invoking the method again:
@CacheResult(cacheName="books", exceptionCacheName="failures"
cachedExceptions = InvalidIsbnNotFoundException.class)
public Book findBook(ISBN isbn)You do not need to do anything specific to enable the JSR-107 support alongside Spring’s
declarative annotation support. Both @EnableCaching and the cache:annotation-driven
XML element automatically enable the JCache support if both the JSR-107 API and the
spring-context-support module are present in the classpath.
|
Note
|
Depending on your use case, the choice is basically yours. You can even mix and match services by using the JSR-107 API on some and using Spring’s own annotations on others. However, if these services impact the same caches, you should use a consistent and identical key generation implementation. |
If annotations are not an option (perhaps due to having no access to the sources or no external code), you can use XML for declarative caching. So, instead of annotating the methods for caching, you can specify the target method and the caching directives externally (similar to the declarative transaction management advice). The example from the previous section can be translated into the following example:
<!-- the service we want to make cacheable -->
<bean id="bookService" class="x.y.service.DefaultBookService"/>
<!-- cache definitions -->
<cache:advice id="cacheAdvice" cache-manager="cacheManager">
<cache:caching cache="books">
<cache:cacheable method="findBook" key="#isbn"/>
<cache:cache-evict method="loadBooks" all-entries="true"/>
</cache:caching>
</cache:advice>
<!-- apply the cacheable behavior to all BookService interfaces -->
<aop:config>
<aop:advisor advice-ref="cacheAdvice" pointcut="execution(* x.y.BookService.*(..))"/>
</aop:config>
<!-- cache manager definition omitted -->In the preceding configuration, the bookService is made cacheable. The caching semantics
to apply are encapsulated in the cache:advice definition, which causes the findBooks
method to be used for putting data into the cache and the loadBooks method for evicting
data. Both definitions work against the books cache.
The aop:config definition applies the cache advice to the appropriate points in the
program by using the AspectJ pointcut expression (more information is available in
Aspect Oriented Programming with Spring). In the preceding example,
all methods from the BookService are considered and the cache advice is applied to them.
The declarative XML caching supports all of the annotation-based model, so moving between
the two should be fairly easy. Furthermore, both can be used inside the same application.
The XML-based approach does not touch the target code. However, it is inherently more
verbose. When dealing with classes that have overloaded methods that are targeted for
caching, identifying the proper methods does take an extra effort, since the method
argument is not a good discriminator. In these cases, you can use the AspectJ pointcut
to cherry pick the target methods and apply the appropriate caching functionality.
However, through XML, it is easier to apply package or group or interface-wide caching
(again, due to the AspectJ pointcut) and to create template-like definitions (as we did
in the preceding example by defining the target cache through the cache:definitions
cache attribute).
The cache abstraction provides several storage integration options. To use them, you need
to declare an appropriate CacheManager (an entity that controls and manages Cache
instances and that can be used to retrieve these for storage).
The JDK-based Cache implementation resides under
org.springframework.cache.concurrent package. It lets you use ConcurrentHashMap
as a backing Cache store. The following example shows how to configure two caches:
<!-- simple cache manager -->
<bean id="cacheManager" class="org.springframework.cache.support.SimpleCacheManager">
<property name="caches">
<set>
<bean class="org.springframework.cache.concurrent.ConcurrentMapCacheFactoryBean" p:name="default"/>
<bean class="org.springframework.cache.concurrent.ConcurrentMapCacheFactoryBean" p:name="books"/>
</set>
</property>
</bean>The preceding snippet uses the SimpleCacheManager to create a CacheManager for the
two nested ConcurrentMapCache instances named default and books. Note that the
names are configured directly for each cache.
As the cache is created by the application, it is bound to its lifecycle, making it suitable for basic use cases, tests, or simple applications. The cache scales well and is very fast, but it does not provide any management, persistence capabilities, or eviction contracts.
Ehcache 3.x is fully JSR-107 compliant and no dedicated support is required for it. See JSR-107 Cache for details.
Caffeine is a Java 8 rewrite of Guava’s cache, and its implementation is located in the
org.springframework.cache.caffeine package and provides access to several features
of Caffeine.
The following example configures a CacheManager that creates the cache on demand:
<bean id="cacheManager"
class="org.springframework.cache.caffeine.CaffeineCacheManager"/>You can also provide the caches to use explicitly. In that case, only those are made available by the manager. The following example shows how to do so:
<bean id="cacheManager" class="org.springframework.cache.caffeine.CaffeineCacheManager">
<property name="cacheNames">
<set>
<value>default</value>
<value>books</value>
</set>
</property>
</bean>The Caffeine CacheManager also supports custom Caffeine and CacheLoader.
See the Caffeine documentation
for more information about those.
GemFire is a memory-oriented, disk-backed, elastically scalable, continuously available,
active (with built-in pattern-based subscription notifications), globally replicated
database and provides fully-featured edge caching. For further information on how to
use GemFire as a CacheManager (and more), see the
{doc-root}/spring-gemfire/docs/current/reference/html/[Spring Data GemFire reference documentation].
Spring’s caching abstraction can also use JSR-107-compliant caches. The JCache
implementation is located in the org.springframework.cache.jcache package.
Again, to use it, you need to declare the appropriate CacheManager.
The following example shows how to do so:
<bean id="cacheManager"
class="org.springframework.cache.jcache.JCacheCacheManager"
p:cache-manager-ref="jCacheManager"/>
<!-- JSR-107 cache manager setup -->
<bean id="jCacheManager" .../>Sometimes, when switching environments or doing testing, you might have cache declarations without having an actual backing cache configured. As this is an invalid configuration, an exception is thrown at runtime, since the caching infrastructure is unable to find a suitable store. In situations like this, rather than removing the cache declarations (which can prove tedious), you can wire in a simple dummy cache that performs no caching — that is, it forces the cached methods to be invoked every time. The following example shows how to do so:
<bean id="cacheManager" class="org.springframework.cache.support.CompositeCacheManager">
<property name="cacheManagers">
<list>
<ref bean="jdkCache"/>
<ref bean="gemfireCache"/>
</list>
</property>
<property name="fallbackToNoOpCache" value="true"/>
</bean>The CompositeCacheManager in the preceding chains multiple CacheManager instances and,
through the fallbackToNoOpCache flag, adds a no-op cache for all the definitions not
handled by the configured cache managers. That is, every cache definition not found in
either jdkCache or gemfireCache (configured earlier in the example) is handled by
the no-op cache, which does not store any information, causing the target method to be
invoked every time.
Clearly, there are plenty of caching products out there that you can use as a backing
store. For those that do not support JSR-107 you need to provide a CacheManager and a
Cache implementation. This may sound harder than it is, since, in practice, the classes
tend to be simple adapters that map the
caching abstraction framework on top of the storage API, as the Caffeine classes do.
Most CacheManager classes can use the classes in the
org.springframework.cache.support package (such as AbstractCacheManager which takes
care of the boiler-plate code, leaving only the actual mapping to be completed).
Directly through your cache provider. The cache abstraction is an abstraction,
not a cache implementation. The solution you use might support various data
policies and different topologies that other solutions do not support (for example,
the JDK ConcurrentHashMap — exposing that in the cache abstraction would be useless
because there would no backing support). Such functionality should be controlled
directly through the backing cache (when configuring it) or through its native API.