<dependency>
        <groupId>com.github.oxo42</groupId>
        <artifactId>stateless4j</artifactId>
        <version>2.5.0</version>
    </dependency>

Create state machines and lightweight state machine-based workflows directly in java code.

StateMachineConfig<State, Trigger> phoneCallConfig = new StateMachineConfig<>();

phoneCallConfig.configure(State.OffHook)
        .permit(Trigger.CallDialed, State.Ringing);

phoneCallConfig.configure(State.Ringing)
        .permit(Trigger.HungUp, State.OffHook)
        .permit(Trigger.CallConnected, State.Connected);

// this example uses Java 8 method references
// a Java 7 example is provided in /examples
phoneCallConfig.configure(State.Connected)
        .onEntry(this::startCallTimer)
        .onExit(this::stopCallTimer)
        .permit(Trigger.LeftMessage, State.OffHook)
        .permit(Trigger.HungUp, State.OffHook)
        .permit(Trigger.PlacedOnHold, State.OnHold);

// ...

StateMachine<State, Trigger> phoneCall =
        new StateMachine<>(State.OffHook, phoneCallConfig);

phoneCall.fire(Trigger.CallDialed);
assertEquals(State.Ringing, phoneCall.getState());

stateless4j is a port of stateless for java

Most standard state machine constructs are supported:

• Generic support for states and triggers of any java type (numbers, strings, enums, etc.)
• Hierarchical states
• Entry/exit events for states
• Guard clauses to support conditional transitions
• Introspection

Some useful extensions are also provided:

• Parameterised triggers
• Reentrant states

In the example below, the OnHold state is a substate of the Connected state. This means that an OnHold call is still connected.

phoneCall.configure(State.OnHold)
    .substateOf(State.Connected)
    .permit(Trigger.TakenOffHold, State.Connected)
    .permit(Trigger.HungUp, State.OffHook)
    .permit(Trigger.PhoneHurledAgainstWall, State.PhoneDestroyed);

In addition to the StateMachine.getState() property, which will report the precise current state, an isInState(State) method is provided. isInState(State) will take substates into account, so that if the example above was in the OnHold state, isInState(State.Connected) would also evaluate to true.

In the example, the startCallTimer() method will be executed when a call is connected. The stopCallTimer() will be executed when call completes (by either hanging up or hurling the phone against the wall.)

The call can move between the Connected and OnHold states without the startCallTimer() and stopCallTimer() methods being called repeatedly because the OnHold state is a substate of the Connected state.

Entry/Exit event handlers can be supplied with a parameter of type Transition that describes the trigger, source and destination states.

Apache 2.0 License