摘要：狀態(tài)機(jī)的使用細(xì)節(jié)上一篇文章介紹了以及三款狀態(tài)機(jī)引擎的實現(xiàn)原理，以及我為何選擇作為解決方案。被代理的默認(rèn)實現(xiàn)為，內(nèi)部描述了狀態(tài)機(jī)實例創(chuàng)建細(xì)節(jié)包括類型信息等，同時也包含了的一些全局共享資源包括等。

date: 2017-06-19 15:50:18

上一篇文章介紹了stateless4j、spring-statemachine以及squirrel-foundation三款狀態(tài)機(jī)引擎的實現(xiàn)原理，以及我為何選擇squirrel-foundation作為解決方案。本文主要介紹一下項目中如何使用squirrel-foundation的一些細(xì)節(jié)以及如何與spring進(jìn)行集成。在閱讀本文前，建議先閱讀官方的使用手冊。

StateMachine: StateMachine實例由StateMachineBuilder創(chuàng)建不被共享，對于使用annotation方式(或fluent api)定義的StateMachine，StateMachine實例即根據(jù)此定義創(chuàng)建，相應(yīng)的action也由本實例執(zhí)行，與spring的集成最終要的就是講spring的bean實例注入給由builder創(chuàng)建的狀態(tài)機(jī)實例；

StateMachineBuilder: 本質(zhì)上是由StateMachineBuilderFactory創(chuàng)建的動態(tài)代理。被代理的StateMachineBuilder默認(rèn)實現(xiàn)為StateMachineBuilderImpl，內(nèi)部描述了狀態(tài)機(jī)實例創(chuàng)建細(xì)節(jié)包括State、Event、Context類型信息、constructor等，同時也包含了StateMachine的一些全局共享資源包括StateConverter、EventConverter、MvelScriptManager等。StateMachineBuilder可被復(fù)用，使用中可被實現(xiàn)為singleton；

StateMachineBuilderFactory: 為StateMachineBuilder創(chuàng)建的動態(tài)代理實例；

狀態(tài)正常遷移
TransitionBegin--(exit->transition->entry)-->TransitionComplete-->TransitionEnd

狀態(tài)遷移異常
TransitionBegin--(exit->transition->entry)-->TransitionException-->TransitionEnd

狀態(tài)遷移事件拒絕
TransitionBegin-->TransitionDeclined-->TransitionEnd

從statemachine的生命流程上可以看到，StateMachineBuilder可以單例方式由spring container管理，而stateMachine的instance的生命周期伴隨著請求(或業(yè)務(wù))。
從這兩點出發(fā)，集成spring需要完成兩件事：

(1).通過Spring創(chuàng)建StateMachineBuilder實例；

(2).業(yè)務(wù)函數(shù)中通過(1)的StateMachineBuilder實例創(chuàng)建StateMachine實例，并向StateMachine暴露SpringApplicationContext；

泛型參數(shù)+覆蓋默認(rèn)構(gòu)造函數(shù)隱藏StateMachineBuilder創(chuàng)建細(xì)節(jié)，實現(xiàn)ApplicationContextAware接口，接受applicationContext注入，并注入給stateMachine實例。

public abstract class AbstractStateMachineEngine implements ApplicationContextAware {
    protected UntypedStateMachineBuilder stateMachineBuilder = null;
    @SuppressWarnings("unchecked")
    public AbstractStateMachineEngine() {
        //識別泛型參數(shù)
        Class genericType = (Class)GenericTypeResolver.resolveTypeArgument(getClass(),
            AbstractStateMachineEngine.class);
        stateMachineBuilder = StateMachineBuilderFactory.create(genericType, ApplicationContext.class);
    }
    //注入applicationContext，并在創(chuàng)建StateMachine實例時注入
    @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
                            //暫時開啟debug進(jìn)行日志trace
                            StateMachineConfiguration.create().enableDebugMode(true).enableAutoStart(true),
                            //注入applicationContext
                            applicationContext);
        stateMachine.fire(trigger, context);
    }
    ...
}
@Service
class DiscountRefundStateMachineEngine extends AbstractStateMachineEngine {
}
@Service
public class ReturnGoodsStateMachineEngine extends AbstractStateMachineEngine {
}

StateMachine定義，接受SpringContext注入

@StateMachineParameters(stateType = State.class, eventType = Trigger.class,
    //StateMachineContext 自定義上下文，用來傳遞數(shù)據(jù)
    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;
    //定義構(gòu)造函數(shù)接受ApplicationContext注入([參看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
    }
    ...
}

從StateMachine的事件響應(yīng)流程中可以看到，TransitionBegin--(exit->transition->entry)-->TransitionComplete-->TransitionEnd，在TransitionComplete發(fā)生一個狀態(tài)已從source遷移到了target狀態(tài)，所以我選擇了在這個時間點進(jìn)行了狀態(tài)的持久化（沒有選擇TransitionEnd做持久化，因為某些場景在持久化完成后還會存在一些外部動作的觸發(fā)，例如通知第三方系統(tǒng)當(dāng)前狀態(tài)已完成變更）。

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;
            //從上下文中獲取需要持久化的數(shù)據(jù)，例如訂單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());
        }
    }
}

由于StateMachine實例不是由Spring容器創(chuàng)建，所以這個過程中無法通過注解方式開啟事務(wù)(Spring沒有機(jī)會去創(chuàng)建事務(wù)代理)，我采用了編程式事務(wù)，在AbstractStateMachineEngine的fire函數(shù)中隱式的實現(xiàn)。
AbstractStateMachineEngine#fire

public abstract class AbstractStateMachineEngine implements ApplicationContextAware {
    ...
    public void fire(int rmaId, State initialState, Trigger trigger, StateMachineContext context) {
        JedisLock jedisLock = jedisLockFactory.buildLock(rmaId);
        //爭用分布式鎖
        if (jedisLock.tryLock()) {
            try {
                T stateMachine = stateMachineBuilder.newUntypedStateMachine(
                                    initialState
                                    //暫時開啟debug進(jìn)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();
            }
        } 
        ...
    }
}

squirrel statemachine提供了DotVisitor、SCXMLVisitor兩種實現(xiàn)方式用于生成狀態(tài)機(jī)描述文件，項目里我選擇了graphviz用來做狀態(tài)拓?fù)?br>graphviz gui工具下載
PS:由于squirrel默認(rèn)的DotVisitorImpl對帶中文描述屬性的State/Event枚舉不友好，我在原有代碼上做了一些調(diào)整，有類似需求的可以看這里

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