Add a sample app with Spring Kafka

.gitignore

@@ -12,6 +12,7 @@ release.properties
 *.iml
 .classpath
 .project
+.factorypath
 .settings/
 .vscode/
 .attach_pid*

examples/pom.xml

@@ -28,6 +28,7 @@
         <module>spring-reactive</module>
         <module>spring-rsocket</module>
         <module>spring-function</module>
+        <module>spring-kafka</module>
     </modules>
 
 </project>

examples/spring-kafka/README.md

@@ -0,0 +1,32 @@
+# Spring Kafka + CloudEvents sample
+
+## Build
+
+```shell
+mvn package
+```
+
+## Start Consumer
+
+```shell
+mvn spring-boot:run
+```
+
+You can try sending a request using any kafka client, or using the integration tests in this project. You send to the "in" topic and it echos back a cloud event on the "out" topic. The listener is implemented like this (the request and response are modelled directly as a `CloudEvent`):
+
+```java
+@KafkaListener(id = "listener", topics = "in", clientIdPrefix = "demo")
+@SendTo("out")
+public CloudEvent listen(CloudEvent event) {
+    return ...;
+}
+```
+
+and to make that work we need to install the Kafka message converter as a `@Bean`:
+
+```java
+@Bean
+public CloudEventRecordMessageConverter recordMessageConverter() {
+    return new CloudEventRecordMessageConverter();
+}
+```

examples/spring-kafka/pom.xml

@@ -0,0 +1,82 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <artifactId>cloudevents-examples</artifactId>
+        <groupId>io.cloudevents</groupId>
+        <version>2.1.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>cloudevents-spring-kafka-example</artifactId>
+
+    <properties>
+        <spring-boot.version>2.4.3</spring-boot.version>
+        <testcontainers.version>1.15.2</testcontainers.version>
+    </properties>
+
+    <dependencyManagement>
+        <dependencies>
+            <dependency>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-dependencies</artifactId>
+                <version>${spring-boot.version}</version>
+                <type>pom</type>
+                <scope>import</scope>
+            </dependency>
+            <dependency>
+                <groupId>org.testcontainers</groupId>
+                <artifactId>testcontainers-bom</artifactId>
+                <version>${testcontainers.version}</version>
+                <type>pom</type>
+                <scope>import</scope>
+            </dependency>
+        </dependencies>
+    </dependencyManagement>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>io.cloudevents</groupId>
+            <artifactId>cloudevents-spring</artifactId>
+            <version>${project.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.kafka</groupId>
+            <artifactId>spring-kafka</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>io.cloudevents</groupId>
+            <artifactId>cloudevents-json-jackson</artifactId>
+            <version>${project.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.kafka</groupId>
+            <artifactId>spring-kafka-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.testcontainers</groupId>
+            <artifactId>kafka</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-maven-plugin</artifactId>
+                <version>${spring-boot.version}</version>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>

examples/spring-kafka/src/main/java/io/cloudevents/examples/spring/DemoApplication.java

@@ -0,0 +1,58 @@
+package io.cloudevents.examples.spring;
+
+import java.net.URI;
+import java.util.UUID;
+
+import org.apache.kafka.clients.admin.NewTopic;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.kafka.annotation.KafkaListener;
+import org.springframework.kafka.config.TopicBuilder;
+import org.springframework.messaging.handler.annotation.SendTo;
+
+import io.cloudevents.CloudEvent;
+import io.cloudevents.core.builder.CloudEventBuilder;
+import io.cloudevents.spring.kafka.CloudEventRecordMessageConverter;
+
+@SpringBootApplication
+public class DemoApplication {
+
+    public static void main(String[] args) throws Exception {
+        SpringApplication.run(DemoApplication.class, args);
+    }
+
+    @KafkaListener(id = "listener", topics = "in", clientIdPrefix = "demo")
+    @SendTo("out")
+    public CloudEvent listen(CloudEvent event) {
+        System.err.println("Echo: " + event);
+        return CloudEventBuilder.from(event).withId(UUID.randomUUID().toString())
+                .withSource(URI.create("https://spring.io/foos")).withType("io.spring.event.Foo")
+                .withData(event.getData().toBytes()).build();
+    }
+
+    @Bean
+    public NewTopic topicOut() {
+        return TopicBuilder.name("out").build();
+    }
+
+    @Bean
+    public NewTopic topicIn() {
+        return TopicBuilder.name("in").build();
+    }
+
+    @Configuration
+    public static class CloudEventMessageConverterConfiguration {
+        /**
+         * Configure a RecordMessageConverter for Spring Kafka to pick up and use to
+         * convert to and from CloudEvent and Message.
+         */
+        @Bean
+        public CloudEventRecordMessageConverter recordMessageConverter() {
+            return new CloudEventRecordMessageConverter();
+        }
+
+    }
+
+}

examples/spring-kafka/src/main/java/io/cloudevents/examples/spring/Foo.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2019-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.cloudevents.examples.spring;
+
+class Foo {
+
+	private String value;
+
+	public Foo() {
+	}
+
+	public Foo(String value) {
+		this.value = value;
+	}
+
+	public String getValue() {
+		return this.value;
+	}
+
+	public void setValue(String value) {
+		this.value = value;
+	}
+
+	@Override
+	public String toString() {
+		return "Foo [value=" + this.value + "]";
+	}
+
+}

examples/spring-kafka/src/main/resources/application.properties

@@ -0,0 +1,4 @@
+spring.kafka.producer.value-serializer=org.apache.kafka.common.serialization.ByteArraySerializer
+spring.kafka.producer.key-serializer=org.apache.kafka.common.serialization.ByteArraySerializer
+spring.kafka.consumer.value-deserializer=org.apache.kafka.common.serialization.ByteArrayDeserializer
+spring.kafka.consumer.key-deserializer=org.apache.kafka.common.serialization.ByteArrayDeserializer