mina statemachine解读（一）

statemachine(状态机)在维护多状态数据时有非常好的作用，现在github上star排名最前的是squirrel-foundation以及spring-statemachine，而mina的statemachine好像并没有对外提供，多用于mina的高级特性里面。

了解了下spring-statemachine，提供特别完善的扩展方式，interceptor，listener，甚至支持分布式，但是上手使用还是有一定的难度，代码也比较复杂，状态机的实例比较重。没有看到较好的现实应用实例，如对一个任务的管理可能是需要根据ID从数据库中获取状态再根据当前状态，事件去决定transition，看到spring中是使用PersistStateMachineHandler来处理类似的情况，需要停止状态机，重置状态机为相应状态再触发，感觉不是很优雅，也可能是我看的不够深入没有理解其精髓，如果有别的实现方式欢迎留言告知。

squirrel-foundation相比较spring上手就容易很多了，有很完善的帮助示例，应用也比较符合对状态机的认知，同时也提供了完善的linstener等支持，是比较好的状态机选择。

这里主要介绍mina statemachine，相比前两个可以说寥寥无名，但是在用起来的时候还是很爽的，比较符合现实业务对状态机的要求。核心代码也就几百行，实现逻辑足够清晰，看完源码半个小时就够了，也可以根据自己的业务需求进行修改定制。

mina statemachine的guide：http://mina.apache.org/mina-project/userguide/ch14-state-machine/ch14-state-machine.html，有对应的maven gav。

先上示例吧

/**
 * 任务实体
 * @author 鱼蛮 on 2019/2/23
 **/
@Getter
@Setter
public class Task {
    /**任务ID*/
    private Integer id;
    /**任务名称*/
    private String name;
    /**任务状态*/
    private String state;
}

/**
 * @author 鱼蛮 on 2019/2/23
 **/
public interface TaskWork {
    /**
     * 任务领取
     * @param taskId
     * @param userName
     */
    void take(Integer taskId, String userName);

    /**
     * 任务提交
     * @param taskId
     */
    void submit(Integer taskId);

    /**
     * 任务审核
     * @param taskId
     * @param auditor
     */
    void audit(Integer taskId, String auditor);
}

/**
 * @author 鱼蛮 on 2019/2/23
 **/
@Slf4j
public class TaskHandler {
    @State public static final String CREATED = "Created";
    @State public static final String TOOK = "Took";
    @State public static final String SUBMITTED = "Submitted";
    @State public static final String AUDITED = "Audited";

    @Transition(on = "take", in = CREATED, next = TOOK)
    public void takeTask(StateContext context, String userName) {
        Task task = (Task)context.getAttribute("task");
        log.info("use:{},take task, taskId:{}", userName, task.getId());
    }

    @Transition(on = "submit", in = {TOOK}, next = SUBMITTED)
    public void submitTask(StateContext context) {
        Task task = (Task)context.getAttribute("task");
        log.info("taskId:{}, submitted", task.getId());
    }

    @Transition(on = "audit", in = SUBMITTED, next = AUDITED)
    public void auditTask(StateContext context, String auditor) {
        Task task = (Task)context.getAttribute("task");
        log.info("auditor:{}, audit task {}", auditor, task.getId());
    }
}

/**
 * @author 鱼蛮 on 2019/2/23
 **/
public class TaskSmTest {
    public static void main(String[] args) {
        // 新建handler
        TaskHandler taskHandler = new TaskHandler();
        // 构建状态机
        StateMachine sm = StateMachineFactory.getInstance(Transition.class).create(TaskHandler.CREATED, taskHandler);
        // 创建对外接口对象
        TaskWork taskWork = new StateMachineProxyBuilder().setStateContextLookup(new StateContextLookup() {
            @Override
            public StateContext lookup(Object[] objects) {
                Integer taskId = (Integer)objects[0];
                // 这里应该是根据Id去数据库查询
                Task task = new Task();
                task.setId(taskId);
                StateContext context = new DefaultStateContext();
                if (taskId == 123) {
                    task.setState(TaskHandler.CREATED);
                } else if (taskId == 124) {
                    task.setState(TaskHandler.TOOK);
                } else if (taskId == 125) {
                    task.setState(TaskHandler.SUBMITTED);
                }
                context.setCurrentState(sm.getState(task.getState()));
                context.setAttribute("task", task);
                return context;
            }
        }).create(TaskWork.class, sm);


        taskWork.take(123, "Jack");
        taskWork.submit(124);
        taskWork.audit(125, "Andy");

        StateContext context = new DefaultStateContext();
        context.setCurrentState(sm.getState(TaskHandler.CREATED));
        context.setAttribute("task", new Task());
        Event event = new Event("take", context, new Object[]{123, "Jack"});
        sm.handle(event);

　　　　 taskWork.submit(123);

} }

输出结果为：

2019-02-23 15:50:54,570  INFO [main] (TaskHandler.java:22) - use:Jack,take task, taskId:123
2019-02-23 15:50:54,574  INFO [main] (TaskHandler.java:28) - taskId:124, submitted
2019-02-23 15:50:54,574  INFO [main] (TaskHandler.java:34) - auditor:Andy, audit task 125
2019-02-23 15:50:54,575  INFO [main] (TaskHandler.java:22) - use:Jack,take task, taskId:null
Exception in thread "main" org.apache.mina.statemachine.event.UnhandledEventException: Unhandled event: Event[id=submit,context=StateContext[currentState=State[id=Created],attributes={task=com.blackbread.statemachine.mina.Task@4f8e5cde}],arguments={123}]
    at org.apache.mina.statemachine.StateMachine.handle(StateMachine.java:275)
    at org.apache.mina.statemachine.StateMachine.processEvents(StateMachine.java:170)
    at org.apache.mina.statemachine.StateMachine.handle(StateMachine.java:158)
    at org.apache.mina.statemachine.StateMachineProxyBuilder$MethodInvocationHandler.invoke(StateMachineProxyBuilder.java:261)
    at com.sun.proxy.$Proxy5.submit(Unknown Source)
    at com.blackbread.statemachine.mina.TaskSmTest.main(TaskSmTest.java:55)

 来分析下状态机的创建以及执行流程，首先看这一行是状态机的创建，初始化

        StateMachine sm = StateMachineFactory.getInstance(Transition.class).create(TaskHandler.CREATED, taskHandler);

getInstance方法中获取传入的transitionAnnotation指定的TransitionAnnotation.class，以此作为查找trastition的注解，同时创建StateMachineFactory对象

create方法执行StateMachinne的创建

    public StateMachine create(String start, Object handler, Object... handlers) {

        Map<String, State> states = new HashMap<>();
        List<Object> handlersList = new ArrayList<>(1 + handlers.length);
        handlersList.add(handler);
        handlersList.addAll(Arrays.asList(handlers));

　　　　　// 从handler中获取带State注解的状态集合，这里必须是String类型的，如果想用其他类型的需要自己修改源码加以支持　　　　
        LinkedList<Field> fields = new LinkedList<>();
        for (Object h : handlersList) {
            fields.addAll(getFields(h instanceof Class ? (Class<?>) h : h.getClass()));
        }
　　　　 // 根据field创建State对象
        for (State state : createStates(fields)) {
            states.put(state.getId(), state);
        }

        if (!states.containsKey(start)) {
            throw new StateMachineCreationException("Start state '" + start + "' not found.");
        }
　　　　 // 执行transition与State的绑定
        setupTransitions(transitionAnnotation, transitionsAnnotation, entrySelfTransitionsAnnotation,
                exitSelfTransitionsAnnotation, states, handlersList);

        return new StateMachine(states.values(), start);
    }

private static void setupTransitions(Class<? extends Annotation> transitionAnnotation,
            Class<? extends Annotation> transitionsAnnotation,
            Class<? extends Annotation> onEntrySelfTransitionAnnotation,
            Class<? extends Annotation> onExitSelfTransitionAnnotation, Map<String, State> states, Object handler) {

        Method[] methods = handler.getClass().getDeclaredMethods();
        Arrays.sort(methods, new Comparator<Method>() {
            @Override
            public int compare(Method m1, Method m2) {
                return m1.toString().compareTo(m2.toString());
            }
        });

        for (Method m : methods) {
　　　　　　  // 做State与OnEntry,OnExit注解标注的方法进行绑定，在进入transition以及退出时候调用
            setupSelfTransitions(m, onEntrySelfTransitionAnnotation, onExitSelfTransitionAnnotation, states, handler);

            List<TransitionWrapper> transitionAnnotations = new ArrayList<>();
            // 这里是找带有指定的transitionAnnotation注解的方法，如果是将其包装成TransitionWrapper进行保存，在下一步处理中好获取相应数据
            if (m.isAnnotationPresent(transitionAnnotation)) {
                transitionAnnotations.add(new TransitionWrapper(transitionAnnotation, m
                        .getAnnotation(transitionAnnotation)));
            }
            // 处理多个注解的
            if (m.isAnnotationPresent(transitionsAnnotation)) {
                transitionAnnotations.addAll(Arrays.asList(new TransitionsWrapper(transitionAnnotation,
                        transitionsAnnotation, m.getAnnotation(transitionsAnnotation)).value()));
            }

            if (transitionAnnotations.isEmpty()) {
                continue;
            }

            for (TransitionWrapper annotation : transitionAnnotations) {
                Object[] eventIds = annotation.on();
                
                if (eventIds.length == 0) {
                    throw new StateMachineCreationException("Error encountered when processing method " + m
                            + ". No event ids specified.");
                }
                
                if (annotation.in().length == 0) {
                    throw new StateMachineCreationException("Error encountered when processing method " + m
                            + ". No states specified.");
                }

                State next = null;
                
                if (!annotation.next().equals(Transition.SELF)) {
                    next = states.get(annotation.next());
                    
                    if (next == null) {
                        throw new StateMachineCreationException("Error encountered when processing method " + m
                                + ". Unknown next state: " + annotation.next() + ".");
                    }
                }

                for (Object event : eventIds) {
                    if (event == null) {
                        event = Event.WILDCARD_EVENT_ID;
                    }
                    
                    if (!(event instanceof String)) {
                        event = event.toString();
                    }
                    
                    for (String in : annotation.in()) {
                        State state = states.get(in);
                        
                        if (state == null) {
                            throw new StateMachineCreationException("Error encountered when processing method "
                                    + m + ". Unknown state: " + in + ".");
                        }
　　　　　　　　　　　　　　// 这里就是执行State与Transition的绑定，定义了如下的关系：state执行了event，使用什么样的transition进行处理
                        state.addTransition(new MethodTransition(event, next, m, handler), annotation.weight());
                    }
                }
            }
        }
    }

这段代码就是创建状态机的核心代码了，其实主要了就是解析State状态集合，解析Transition标签，做State与Event，Transition的绑定，状态机在使用的时候其实就是先获取State然后获取State上绑定的Transition执行传入的Event。

这里先到状态机的创建吧，再写一个状态机的内部执行流程。