1、多个状态机的搞法
在实际的企业应用中，基本不可能只有一个状态机流程在跑，比如订单，肯定是很多个订单在运行，每个订单都有自己的订单状态机流程，但上一章的例子，大家可以试一下，当执行到一个状态时，再次刷新页面，不会有任何日志出现，当一个状态流程执行到某个状态，再次执行这个状态，是不会有任何输出的，因为状态机的机制是只有在状态切换的时候才会事件（event）触发，所以我们这一章讲多个状态机的并行执行。
首先，靠上一章例子里面的手打定制一个StateMachineConfig的做法，就只能是有一个状态机流程制霸整个项目，这种霸道的做法肯定是不行啦，要想多个状态机流程并行，那么就要请builder出场了，看代码：
private final static String MACHINEID = "orderMachine";
public StateMachine<OrderStates, OrderEvents> build(BeanFactory beanFactory) throws Exception {
StateMachineBuilder.Builder<OrderStates, OrderEvents> builder = StateMachineBuilder.builder();
System.out.println("构建订单状态机");
builder.configureConfiguration()
.withConfiguration()
.machineId(MACHINEID)
.beanFactory(beanFactory);
builder.configureStates()
.withStates()
.initial(OrderStates.UNPAID)
.states(EnumSet.allOf(OrderStates.class));
builder.configureTransitions()
.withExternal()
.source(OrderStates.UNPAID).target(OrderStates.WAITING_FOR_RECEIVE)
.event(OrderEvents.PAY).action(action())
.and()
.withExternal()
.source(OrderStates.WAITING_FOR_RECEIVE).target(OrderStates.DONE)
.event(OrderEvents.RECEIVE);
return builder.build();
}有没有似曾相识的感觉，里面描述订单状态机的初始状态，状态机的流程代码和StateMachineConfig几乎是一样的，但是都配置在StateMachineBuilder里面
StateMachineBuilder.Builder<OrderStates, OrderEvents> builder = StateMachineBuilder.builder();这是完整的builder类代码：
import java.util.EnumSet;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.context.annotation.Bean;
import org.springframework.statemachine.StateContext;
import org.springframework.statemachine.StateMachine;
import org.springframework.statemachine.action.Action;
import org.springframework.statemachine.config.StateMachineBuilder;
import org.springframework.stereotype.Component;
@Component
public class OrderStateMachineBuilder {
private final static String MACHINEID = "orderMachine";
/**
* 构建状态机
*
* @param beanFactory
* @return
* @throws Exception
*/
public StateMachine<OrderStates, OrderEvents> build(BeanFactory beanFactory) throws Exception {
StateMachineBuilder.Builder<OrderStates, OrderEvents> builder = StateMachineBuilder.builder();
System.out.println("构建订单状态机");
builder.configureConfiguration()
.withConfiguration()
.machineId(MACHINEID)
.beanFactory(beanFactory);
builder.configureStates()
.withStates()
.initial(OrderStates.UNPAID)
.states(EnumSet.allOf(OrderStates.class));
builder.configureTransitions()
.withExternal()
.source(OrderStates.UNPAID).target(OrderStates.WAITING_FOR_RECEIVE)
.event(OrderEvents.PAY).action(action())
.and()
.withExternal()
.source(OrderStates.WAITING_FOR_RECEIVE).target(OrderStates.DONE)
.event(OrderEvents.RECEIVE);
return builder.build();
}
@Bean
public Action<OrderStates, OrderEvents> action() {
return new Action<OrderStates, OrderEvents>() {
@Override
public void execute(StateContext<OrderStates, OrderEvents> context) {
System.out.println(context);
}
};
}
}在完整的代码里面我们看到有个东西没讲，那就是MACHINEID，在builder的配置代码里面，有这么一段
builder.configureConfiguration()
.withConfiguration()
.machineId(MACHINEID)
.beanFactory(beanFactory);machineId是状态机的配置类和事件实现类的关联，和它关联的是OrderEventConfig，代码如下：
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.messaging.Message;
import org.springframework.statemachine.annotation.OnTransition;
import org.springframework.statemachine.annotation.WithStateMachine;
@WithStateMachine(id="orderMachine")
public class OrderEventConfig {
private Logger logger = LoggerFactory.getLogger(getClass());
/**
* 当前状态UNPAID
*/
@OnTransition(target = "UNPAID")
public void create() {
logger.info("---订单创建，待支付---");
}
......
}
这个后面的内容和上一章的OrderSingleEventConfig一模一样，但在类的上面注解了这一句：
@WithStateMachine(id="orderMachine")这个id对应的就是OrderStateMachineBuilder 里面的MACHINEID，被builder写到.machineId(MACHINEID)里面。这样，OrderStateMachineBuilder对应上一章的StateMachineConfig多个状态机的实现版本，OrderEventConfig对应上一章的OrderSingleEventConfig，基本一样，只是和OrderStateMachineBuilder通过machineid做了关联。
现在我们来看怎么用上它。在controller里面引用这个类：
@Autowired
private OrderStateMachineBuilder orderStateMachineBuilder;然后使用它
@RequestMapping("/testOrderState")
public void testOrderState(String orderId) throws Exception {
StateMachine<OrderStates, OrderEvents> stateMachine = orderStateMachineBuilder.build(beanFactory);
// 创建流程
stateMachine.start();
// 触发PAY事件
stateMachine.sendEvent(OrderEvents.PAY);
// 触发RECEIVE事件
stateMachine.sendEvent(OrderEvents.RECEIVE);
// 获取最终状态
System.out.println("最终状态：" + stateMachine.getState().getId());
}这其实就是每次请求testOrderState就会生成一个新的statemachine，所以每次刷新testOrderState请求都会看到日志显示：
构建订单状态机
orderMachine
2019-05-03 19:24:23.734 INFO 11752 --- [nio-9991-exec-1] tConfig$$EnhancerBySpringCGLIB$$29e58541 : ---订单创建，待支付---
2019-05-03 19:24:23.754 INFO 11752 --- [nio-9991-exec-1] o.s.s.support.LifecycleObjectSupport : started org.springframework.statemachine.support.DefaultStateMachineExecutor@133d52dd
2019-05-03 19:24:23.755 INFO 11752 --- [nio-9991-exec-1] o.s.s.support.LifecycleObjectSupport : started UNPAID DONE WAITING_FOR_RECEIVE / UNPAID / uuid=52b44103-22af-49cc-a645-3aab29212a9e / id=orderMachine
DefaultStateContext [stage=TRANSITION, message=GenericMessage [payload=PAY, headers={id=ed826b85-e069-9a5e-34a1-d78454183143, timestamp=1556882663765}], messageHeaders={id=ade4055c-9b59-6498-501e-0e2a8cfe04b4, _sm_id_=52b44103-22af-49cc-a645-3aab29212a9e, timestamp=1556882663767}, extendedState=DefaultExtendedState [variables={}], transition=AbstractTransition [source=ObjectState [getIds()=[UNPAID], getClass()=class org.springframework.statemachine.state.ObjectState, hashCode()=1027927242, toString()=AbstractState [id=UNPAID, pseudoState=org.springframework.statemachine.state.DefaultPseudoState@4b05dcc, deferred=[], entryActions=[], exitActions=[], stateActions=[], regions=[], submachine=null]], target=ObjectState [getIds()=[WAITING_FOR_RECEIVE], getClass()=class org.springframework.statemachine.state.ObjectState, hashCode()=422378, toString()=AbstractState [id=WAITING_FOR_RECEIVE, pseudoState=null, deferred=[], entryActions=[], exitActions=[], stateActions=[], regions=[], submachine=null]], kind=EXTERNAL, guard=null], stateMachine=UNPAID DONE WAITING_FOR_RECEIVE / UNPAID / uuid=52b44103-22af-49cc-a645-3aab29212a9e / id=orderMachine, source=null, target=null, sources=null, targets=null, exception=null]
传递的参数：null
2019-05-03 19:24:23.775 INFO 11752 --- [nio-9991-exec-1] tConfig$$EnhancerBySpringCGLIB$$29e58541 : ---用户完成支付，待收货---
传递的参数：null
传递的参数：null
2019-05-03 19:24:23.782 INFO 11752 --- [nio-9991-exec-1] tConfig$$EnhancerBySpringCGLIB$$29e58541 : ---用户已收货，订单完成---
最终状态：DONE
这和之前执行testSingleOrderState是不一样的，testSingleOrderState只有第一次会有日志打出，再执行就没有日志出来了，而testOrderState因为每次都build一个新的statemachine，所以每次都会显示日志出来，这样就能保证每个订单都可以为它build一个新的statemachine，就解决了多个状态机并行执行的问题了。
虽然多个状态机的问题解决了，但是对于实际的企业应用而言，还是有问题。这种简单粗暴的，来一个请求就新增一个状态机的搞法很不经济，而且状态机也不是越多越好，而应该是和业务对象一一对应才行，比如订单，就是一个订单一个状态机，而不是每次订单变化就build的一个。这个问题就用到了状态机的持久化，我们下一章就谈谈持久化问题。
2、有个坑
EventConfig类的@WithStateMachine注解有两个参数可用
public @interface WithStateMachine {
/**
* The name of a state machine bean which annotated bean should be associated.
* Defaults to {@code stateMachine}
*
* @return the state machine bean name
*/
String name() default StateMachineSystemConstants.DEFAULT_ID_STATEMACHINE;
/**
* The id of a state machine which annotated bean should be associated.
*
* @return the state machine id
* @see StateMachine#getId()
*/
String id() default "";
}我们在上面是用id来关联StateMachineBuilder和EventConfig的，用name是无效的，但这个id是spring-statemachine-starter，2.x版本才有，在1.x版本里面，只有name参数，用name参数StateMachineBuilder和EventConfig关联不上，也就是在builder里面状态变化，eventConfig里面并不会同步触发事件，请大家确认使用的是2.x的版本，这都是我血与泪的忠告。