Java State Machine

This is a simple event based state machine library written in java to avoid any boiler plate code around writing if-else/switch cases around state changes for a particular entity. It interprets the current state, new state and event fired to verify if it is a valid transition.

Status

Java State Machine is currently in a very nascent stage and has a lot improvement scope around making it more generic and addition of more features around state management.

Usage

for Maven

<dependency>
    <groupId>com.himanshuvirmani</groupId>
    <artifactId>java-state-machine</artifactId>
    <version>1.0.5</version>
</dependency>

for Gradle

repositories {
    mavenCentral()
}

dependencies {
    compile("com.himanshuvirmani:java-state-machine:1.0.5") {
        exclude group: 'org.projectlombok', module: 'lombok' //do this if you are already include lombok in you dependencies 
        exclude group: 'org.slf4j', module: 'slf4j-simple' //do this if you are already include slf4j in you dependencies
    }
}

Sample Code

You can find a working sample project in this repository which showcases some of the features of the library. Find below some excerpts from the same sample project on how to use the library.

Initialize

StateMachine<MySampleState, MySampleEvent, Object> stateMachine =
                new StateMachine<MySampleState, MySampleEvent, Object>(MySampleState.CREATED);

Creating Transitions

• Individual Transition

stateMachine.transition().from(MySampleState.CREATED).to(MySampleState.ONHOLD).on(MySampleEvent.HOLD).setOnSuccessListener(onSuccessListener).create();

stateMachine.transition().from(MySampleState.ONHOLD).to(MySampleState.DELIVERED).on(MySampleEvent.DELIVER).create();

• Using Single line Transitions Examples

stateMachine.transitions().fromAny(MySampleState.CREATED, MySampleState.ONHOLD).toAmong(MySampleState.ONHOLD, MySampleState.DELIVERED).on(MySampleEvent.HOLD, MySampleEvent.DELIVER).create();

stateMachine.transitions().fromAny(MySampleState.CREATED, MySampleState.ONHOLD).toAmong(MySampleState.ONHOLD, MySampleState.DELIVERED).on(MySampleEvent.DELIVER).create();

stateMachine.transitions().fromAny(MySampleState.CREATED, MySampleState.ONHOLD).on(MySampleEvent.DELIVER).ignore().create();

• Using Conditional Transitions Example. You can catch TransitionConditionNotMetException to ignore state change when condition is not met.

stateMachine.transition().from(MySampleState.CREATED).to(MySampleState.ONHOLD).on(MySampleEvent.HOLD).when(new Condition() {
    @Override
    public boolean isMet() {
        return a == b;
    }
}).create();

Firing an event

try {
    stateMachine.fire(MySampleEvent.HOLD);
} catch (TransitionException e) {
    e.printStackTrace();
}

Additionally you can have StateChangeListener

MyEntityClass implements StateMachine.StateChangeListener<MySampleState, MySampleEvent>{

@Override
public void onStateChanged(MySampleState from, MySampleState to, MySampleEvent on) {
    log.info("State changed from " + from + " to " + to + " on " + on);
}

To Do

1. State Exit and Entry Listeners.
2. Better Java Docs
3. More features as and when they come.