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squirrel-foundation状态机的使用细节

上一篇文章介绍了stateless4j、spring-statemachine以及squirrel-foundation三款状态机引擎的实现原理，以及我为何选择squirrel-foundation作为解决方案。本文主要介绍一下项目中如何使用squirrel-foundation的一些细节以及如何与spring进行集成。在阅读本文前，建议先阅读官方的使用手册。

生命周期

状态机创建过程

StateMachine: StateMachine实例由StateMachineBuilder创建不被共享，对于使用annotation方式(或fluent api)定义的StateMachine，StateMachine实例即根据此定义创建，相应的action也由本实例执行，与spring的集成最终要的就是讲spring的bean实例注入给由builder创建的状态机实例；StateMachineBuilder: 本质上是由StateMachineBuilderFactory创建的动态代理。被代理的StateMachineBuilder默认实现为StateMachineBuilderImpl，内部描述了状态机实例创建细节包括State、Event、Context类型信息、constructor等，同时也包含了StateMachine的一些全局共享资源包括StateConverter、EventConverter、MvelScriptManager等。StateMachineBuilder可被复用，使用中可被实现为singleton；StateMachineBuilderFactory: 为StateMachineBuilder创建的动态代理实例；

事件处理过程

状态正常迁移 TransitionBegin--(exit->transition->entry)-->TransitionComplete-->TransitionEnd状态迁移异常 TransitionBegin--(exit->transition->entry)-->TransitionException-->TransitionEnd状态迁移事件拒绝 TransitionBegin-->TransitionDeclined-->TransitionEnd

spring集成

从statemachine的生命流程上可以看到，StateMachineBuilder可以单例方式由spring container管理，而stateMachine的instance的生命周期伴随着请求(或业务)。 从这两点出发，集成spring需要完成两件事：

(1).通过Spring创建StateMachineBuilder实例；(2).业务函数中通过(1)的StateMachineBuilder实例创建StateMachine实例，并向StateMachine暴露SpringApplicationContext；

泛型参数+覆盖默认构造函数隐藏StateMachineBuilder创建细节，实现ApplicationContextAware接口，接受applicationContext注入，并注入给stateMachine实例。

public abstract class AbstractStateMachineEngine<T extends UntypedStateMachine> implements ApplicationContextAware { protected UntypedStateMachineBuilder stateMachineBuilder = null; @SuppressWarnings("unchecked") public AbstractStateMachineEngine() { //识别泛型参数 Class<T> genericType = (Class<T>)GenericTypeResolver.resolveTypeArgument(getClass(), AbstractStateMachineEngine.class); stateMachineBuilder = StateMachineBuilderFactory.create(genericType, ApplicationContext.class); } //注入applicationContext，并在创建StateMachine实例时注入 @Override public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { this.applicationContext = applicationContext; } //delegate fire public void fire(int rmaId, State initialState, Trigger trigger, StateMachineContext context) { T stateMachine = stateMachineBuilder.newUntypedStateMachine( initialState //暂时开启debug进行日志trace StateMachineConfiguration.create().enableDebugMode(true).enableAutoStart(true), //注入applicationContext applicationContext); stateMachine.fire(trigger, context); } ... } @Service class DiscountRefundStateMachineEngine extends AbstractStateMachineEngine<DiscountRefundStateMachine> { } @Service public class ReturnGoodsStateMachineEngine extends AbstractStateMachineEngine<ReturnGoodsStateMachine> { }

StateMachine定义，接受SpringContext注入

@StateMachineParameters(stateType = State.class, eventType = Trigger.class, //StateMachineContext 自定义上下文，用来传递数据 contextType = StateMachineContext.class) @States({ @State(name = "PENDING", initialState = true), @State(name = "CONFIRMING"), @State(name = "REJECTED"), @State(name = "REFUND_APPROVING"), @State(name = "REFUND_APPROVED"), @State(name = "REFUND_FINISHED") }) @Transitions({ @Transit(from = "PENDING", to = "CONFIRMING", on = "APPLY_CONFIRM", callMethod = "doSomething"), @Transit(from = "CONFIRMING", to = "REJECTED", on = "REJECT"), @Transit(from = "CONFIRMING", to = "REFUND_APPROVING", on = "APPLY_APPROVED"), @Transit(from = "REFUND_APPROVING", to = "REFUND_APPROVED", on = "REFUND_APPROVED"), @Transit(from = "REFUND_APPROVED", to = "REFUND_FINISHED", on = "REFUND_FINISH_CONFIRM") }) public class DiscountRefundStateMachine extends AbstractUntypedStateMachine { protected ApplicationContext applicationContext; //定义构造函数接受ApplicationContext注入([参看New State Machine Instance](http://hekailiang.github.io/squirrel/)) public DiscountRefundStateMachine(ApplicationContext applicationContext) { this.applicationContext = applicationContext; } public void doSomething(State fromState, State toState, Trigger event, StateMachineContext stateMachineContext) { DemoBean demoBean = this.applicationContext.get("demoBean"); //do something } ... }

状态持久化

从StateMachine的事件响应流程中可以看到，TransitionBegin--(exit->transition->entry)-->TransitionComplete-->TransitionEnd，在TransitionComplete发生一个状态已从source迁移到了target状态，所以我选择了在这个时间点进行了状态的持久化（没有选择TransitionEnd做持久化，因为某些场景在持久化完成后还会存在一些外部动作的触发，例如通知第三方系统当前状态已完成变更）。

public class DiscountRefundStateMachine extends AbstractUntypedStateMachine { .. @Override protected void afterTransitionCompleted(Object fromState, Object toState, Object event, Object context) { if (context instanceof StateMachineContext && toState instanceof State) { StateMachineContext stateMachineContext = (StateMachineContext)context; //从上下文中获取需要持久化的数据，例如订单ID等 Rma rma = stateMachineContext.get(MessageKeyEnum.RMA); //持久化 rma.setStatus((State)toState); this.applicationContext.get("rmaRepository").updateRma(rma); } else { throw new Exception("type not support, context expect " + StateMachineContext.class.getSimpleName() + ", actually " + context.getClass().getSimpleName() + ", state expect " + State.class.getSimpleName() + ", actually " + toState.getClass().getSimpleName()); } } }

分布式锁+事务

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