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然后通过Event查找相应的Transition进行执行了。
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。
原文地址：https://www.cnblogs.com/lcxdever/p/10422917.html
时间： 2024-10-06 13:03:20