stateless4scala - lightweight state machine for scala

stateless4scala is a port of stateless4j for scala

stateless4j is a port of stateless for java

Introduction

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

val phoneCallConfig = new StateMachineConfig[State, Trigger]

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

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

phoneCallConfig.configure(State.Connected)
  .onEntry(startCallTimer)
  .onExit(stopCallTimer)
  .permit(Trigger.LeftMessage, State.OffHook)
  .permit(Trigger.HungUp, State.OffHook)
  .permit(Trigger.PlacedOnHold, State.OnHold)

// ...

val phoneCall = new StateMachine[State, Trigger](State.OffHook, phoneCallConfig)

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

Features

Most standard state machine constructs are supported:

Generic support for states and triggers of any java/scala 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

Hierarchical 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.

Entry/Exit Events

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.

License

Apache 2.0 License

keritaf / stateless4scala