可以看到，编写一个多分支的状态机也是非常简单明了的。5zq拜客生活常识网

三、通过状态机反向生成PlantUml图

5zq拜客生活常识网

没想到吧，还能通过代码定义好的状态机反向生成plantUML图，实现状态机的可视化。（可以用图说话，和产品对比下状态实现的是否正确了。）5zq拜客生活常识网

四、特殊使用示例

1. 不满足状态流转条件时的处理

@Test
public void testConditionNotMeet(){
  StateMachineBuilder builder = StateMachineBuilderFactory.create();
  builder.externalTransition()
  .from(StateMachineTest.States.STATE1)
  .to(StateMachineTest.States.STATE2)
  .on(StateMachineTest.Events.EVENT1)
  .when(checkConditionFalse())
  .perform(doAction());

  StateMachine stateMachine = builder.build("NotMeetConditionMachine");
  StateMachineTest.States target = stateMachine.fireEvent(StateMachineTest.States.STATE1, StateMachineTest.Events.EVENT1, new StateMachineTest.Context());
  Assert.assertEquals(StateMachineTest.States.STATE1,target);
}

可以看到，当checkConditionFalse()执行时，永远不会满足状态流转的条件，则状态不会变化，会直接返回原来的STATE1。相关源码在这里：5zq拜客生活常识网

5zq拜客生活常识网

2. 重复定义相同的状态流转

@Test(expected = StateMachineException.class)
public void testDuplicatedTransition(){
  StateMachineBuilder builder = StateMachineBuilderFactory.create();
  builder.externalTransition()
  .from(StateMachineTest.States.STATE1)
  .to(StateMachineTest.States.STATE2)
  .on(StateMachineTest.Events.EVENT1)
  .when(checkCondition())
  .perform(doAction());

  builder.externalTransition()
  .from(StateMachineTest.States.STATE1)
  .to(StateMachineTest.States.STATE2)
  .on(StateMachineTest.Events.EVENT1)
  .when(checkCondition())
  .perform(doAction());
}

会在第二次builder执行到on(StateMachineTest.Events.EVENT1)函数时，抛出StateMachineException异常。抛出异常在on()的verify检查这里，如下：5zq拜客生活常识网

5zq拜客生活常识网

3. 重复定义状态机

@Test(expected = StateMachineException.class)
public void testDuplicateMachine(){
  StateMachineBuilder builder = StateMachineBuilderFactory.create();
  builder.externalTransition()
  .from(StateMachineTest.States.STATE1)
  .to(StateMachineTest.States.STATE2)
  .on(StateMachineTest.Events.EVENT1)
  .when(checkCondition())
  .perform(doAction());

  builder.build("DuplicatedMachine");
  builder.build("DuplicatedMachine");
}

会在第二次build同名状态机时抛出StateMachineException异常。抛出异常的源码在状态机的注册函数中，如下：