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。

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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

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@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)。

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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

由于StateMachine实例不是由Spring容器创建,所以这个过程中无法通过注解方式开启事务(Spring没有机会去创建事务代理),我采用了编程式事务,在AbstractStateMachineEngine的fire函数中隐式的实现。 AbstractStateMachineEngine#fire

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public abstract class AbstractStateMachineEngine<T extends UntypedStateMachine> implements ApplicationContextAware {
...
public void fire(int rmaId, State initialState, Trigger trigger, StateMachineContext context) {
JedisLock jedisLock = jedisLockFactory.buildLock(rmaId);
//争用分布式锁
if (jedisLock.tryLock()) {
try {
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);
DataSourceTransactionManager transactionManager = applicationContext.get("transactionManager")
DefaultTransactionDefinition def = new DefaultTransactionDefinition();
def.setPropagationBehavior(TransactionDefinition.PROPAGATION_REQUIRED);
TransactionStatus status = transactionManager.getTransaction(def);
try {
stateMachine.fire(trigger, context)
transactionManager.commit(status);
} catch (Exception ex) {
transactionManager.rollback(status);
throw ex;
}
} finally {
jedisLock.release();
}
}
...
}
}

使用graphviz生成状态拓扑图

squirrel statemachine提供了DotVisitor、SCXMLVisitor两种实现方式用于生成状态机描述文件,项目里我选择了graphviz用来做状态拓扑 graphviz gui工具下载 PS:由于squirrel默认的DotVisitorImpl对带中文描述属性的State/Event枚举不友好,我在原有代码上做了一些调整,有类似需求的可以看这里

以上是我在落地状态机改造过程中的一些细节,欢迎大家留意讨论。