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设计模式-观察者模式的拓展
可观察者对象(消息发送者) Java.util.Observalbe观察者 java.util.Observer
标准化接口(标记接口)
事件对象 java.util.EventObject事件监听器 java.util.EventListener
public class ObserverDemo {public static vo…Java 事件/监听器编程模型
设计模式-观察者模式的拓展
可观察者对象(消息发送者) Java.util.Observalbe观察者 java.util.Observer
标准化接口(标记接口)
事件对象 java.util.EventObject事件监听器 java.util.EventListener
public class ObserverDemo {public static void main(String[] args) {Observable observable new EventObservable();observable.addObserver(new EventObserver());observable.notifyObservers(hello);}/*** 因为我们要调用 change 监听者这个方法才能生效 但是这个方法是个protected 所以我们进行拓展* */static class EventObservable extends Observable {public void setChanged(){super.setChanged();}public void notifyObservers(Object args) {setChanged();super.notifyObservers(new EventObject(args));clearChanged();}}static class EventObserver implements Observer, EventListener {Overridepublic void update(Observable o, Object event) {EventObject eventObject (EventObject) event;System.out.println(收到消息: eventObject);}}
}理解 发布事件的是被监听的对向里面会注册监听器也就是需要感知当前对象变化的对象。 JDKEventListener提供了这个标记接口算是一种规范表名这个是事件的监听器。 EventObject 这个也算是一个标准这个对象是方便数据在事件发布的时候进行传递。
面向接口的事件/监听器设计模式 基本模式 一般监听器会继承EventListener 一般事件会继承EventObject
面向注解的事件/监听器设计模式 Spirng 标准事件 ApplicationEvent 基于接口的事件监听器 public static void main(String[] args) {GenericApplicationContext context new GenericApplicationContext();// 注册一个事件监听context.addApplicationListener(new ApplicationListenerApplicationEvent() {Overridepublic void onApplicationEvent(ApplicationEvent event) {System.out.println(event.getTimestamp() 接收到事件 : event);}});context.refresh();context.close();
}可以看到这里收到了两个事件那么事件从哪里发布的呢请看事件发布器。
基于注解的事件监听器 public static void main(String[] args) {AnnotationConfigApplicationContext context new AnnotationConfigApplicationContext();context.register(ApplicatonListenrDemo.class);context.refresh();context.close();
}
EventListener
public void onApplicationEvent(ApplicationEvent applicationEvent) {System.out.println(applicationEvent);
}
// 这样的话就会分类别来处理
EventListener
public void onApplicationEvent(ContextRefreshedEvent applicationEvent) {System.out.println(applicationEvent re);
}// 异步处理
EnableAsync
public class ApplicatonListenrDemo {public static void main(String[] args) {AnnotationConfigApplicationContext context new AnnotationConfigApplicationContext();context.register(ApplicatonListenrDemo.class);context.refresh();context.close();}EventListenerpublic void onApplicationEvent(ApplicationEvent applicationEvent) {System.out.println(applicationEvent);}EventListenerpublic void onApplicationEvent(ContextRefreshedEvent applicationEvent) {System.out.println(applicationEvent re);}EventListenerAsyncpublic void onApplicationEvent(ContextClosedEvent applicationEvent) {System.out.println(applicationEvent);System.out.println(Thread.currentThread().getId());}
}// 控制顺序
public class ApplicatonListenrDemo {public static void main(String[] args) {AnnotationConfigApplicationContext context new AnnotationConfigApplicationContext();context.register(ApplicatonListenrDemo.class);context.refresh();context.close();}EventListenerOrder(2)public void onApplicationEvent2(ContextRefreshedEvent applicationEvent) {System.out.println();}EventListenerOrder(1)public void onApplicationEvent1(ContextRefreshedEvent applicationEvent) {System.out.println(****);}
}注册Spirng ApplicationListenner
方法一 ApplicationListener 作为SpirngBean注册
context.register(MyEventListener.class);
static class MyEventListener implements ApplicationListenerApplicationEvent {Overridepublic void onApplicationEvent(ApplicationEvent event) {System.out.println();}
}方法二通过ConfigrableApplicationContextAPI 注册
context.addApplicationListener(new ApplicationListenerApplicationEvent() {Overridepublic void onApplicationEvent(ApplicationEvent event) {System.out.println(event.getTimestamp() 接收到事件 : event);}
});事件发布器 public class ApplicatonListenrDemo implements ApplicationEventPublisherAware {public static void main(String[] args) {AnnotationConfigApplicationContext context new AnnotationConfigApplicationContext();context.register(ApplicatonListenrDemo.class);context.refresh();context.start();context.close();}EventListenerpublic void onApplicationEvent(ApplicationEvent event) {System.out.println(event);}Overridepublic void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {applicationEventPublisher.publishEvent(new ApplicationEvent(hello) {});// 发布任意对象 重载方法applicationEventPublisher.publishEvent(yes);}
}事件发布器如何找到对应的监听器进行实事件的发布呢? 在发布时间的时候会查缓存缓存如果没有对应的监听器则会更具事件泛型类型进行判断。 根据事件的泛型类型进行判断如果类型符合加入监听器数组。
Spring 事件传播 public static void main(String[] args) {// 1 创建 parent Spring 应用上下文AnnotationConfigApplicationContext parent new AnnotationConfigApplicationContext();parent.setId(parent);parent.register(Mylistener.class);// 创建current spring 应用上下文AnnotationConfigApplicationContext current new AnnotationConfigApplicationContext();current.setId(current);current.register(Mylistener.class);current.setParent(parent);// current parentparent.refresh();current.refresh();parent.close();current.close();}
static class Mylistener implements ApplicationListenerContextRefreshedEvent {Overridepublic void onApplicationEvent(ContextRefreshedEvent event) {System.out.printf(监听到应用上下文[ID %s]\n, event.getApplicationContext().getId());}
}第一个事件触发是parent第二三个由于事件传播子和父都触发了这个事件
原理就是源码会在父也发布事件 如何避免
public class HierachicalEventDemo {public static void main(String[] args) {// 1 创建 parent Spring 应用上下文AnnotationConfigApplicationContext parent new AnnotationConfigApplicationContext();parent.setId(parent);parent.register(Mylistener.class);// 创建current spring 应用上下文AnnotationConfigApplicationContext current new AnnotationConfigApplicationContext();current.setId(current);current.register(Mylistener.class);current.setParent(parent);// current parentparent.refresh();current.refresh();parent.close();current.close();}static class Mylistener implements ApplicationListenerContextRefreshedEvent {/*** 这里之所以要静态是因为我们在 parent 和 current 是不是一样的对象 也就是有两对象* 但是静态字段就是类共用的* 如果时间发布过不再重新发布*/private static SetApplicationEvent processedEvents new LinkedHashSet();Overridepublic void onApplicationEvent(ContextRefreshedEvent event) {if (processedEvents.add(event)) {System.out.printf(监听到应用上下文[ID %s] %s\n , event.getApplicationContext().getId(), event);}}}
}Spirng 内建事件 Spring Payload 事件
使用的时候不能简单继承使用发送方法最好是用object这个方法。
自定义Spirng事件 public class MyEvent extends ApplicationEvent {public MyEvent(String msg) {super(msg);}Overridepublic String getSource() {return (String) super.getSource();}public String getMessage() {return getSource();}
}public class MyListener implements ApplicationListenerMyEvent {Overridepublic void onApplicationEvent(MyEvent event) {System.out.println(event.getMessage());}
}public class Demo {public static void main(String[] args) {AnnotationConfigApplicationContext context new AnnotationConfigApplicationContext();context.register(Mylistener.class);context.refresh();context.publishEvent(new MyEvent(test event));context.close();}
}事件发布注入
ApplicationEventPublisherAwae 回调接口 通过Autowired ApplicationEventPublisher
依赖查找 ApplicationEventMulticaster的底层实现 AbstractContext事件分发布是通过ApplicationEventMulticaster来实现的
同步和异步Spirng事件广播 如果是异步如果要设置Executeor 是需要类型转换的不是基于接口的编程方式。
public class Demo {public static void main(String[] args) {AnnotationConfigApplicationContext context new AnnotationConfigApplicationContext();context.register(Mylistener.class);context.refresh();ApplicationEventMulticaster multicaster context.getBean(ApplicationEventMulticaster.class);if (multicaster instanceof SimpleApplicationEventMulticaster) {ExecutorService executor newSingleThreadExecutor();SimpleApplicationEventMulticaster simpleApplicationEventMulticaster (SimpleApplicationEventMulticaster) multicaster;simpleApplicationEventMulticaster.setTaskExecutor(executor);// 优雅的关闭线程池simpleApplicationEventMulticaster.addApplicationListener(new ApplicationListenerContextClosedEvent() {Overridepublic void onApplicationEvent(ContextClosedEvent event) {if (!executor.isShutdown()) {executor.shutdown();}}});}context.publishEvent(new MyEvent(test event));context.close();}
}通过注解的方式实现
EnableAsync
public class Demo {public static void main(String[] args) {AnnotationConfigApplicationContext context new AnnotationConfigApplicationContext();context.register(Demo.class);context.refresh();context.publishEvent(new MyEvent(test event));context.close();}EventListenerAsyncpublic void onApplicationContext(ApplicationEvent event) {System.out.println(Thread.currentThread().getName() event);}// 这是自定义我们的线程池BeanExecutor taskExecutor() {return Executors.newSingleThreadExecutor();}
}事件的异常情况 public class Demo {public static void main(String[] args) {AnnotationConfigApplicationContext context new AnnotationConfigApplicationContext();context.register(Demo.class);context.refresh();ApplicationEventMulticaster multicaster context.getBean(ApplicationEventMulticaster.class);if (multicaster instanceof SimpleApplicationEventMulticaster) {SimpleApplicationEventMulticaster simpleApplicationEventMulticaster (SimpleApplicationEventMulticaster) multicaster;simpleApplicationEventMulticaster.setErrorHandler((t) -{System.out.printf(发生了异常 );});}context.publishEvent(new MyEvent(test event));context.close();}EventListenerpublic void onApplicationContext(ContextClosedEvent event) {System.out.println(Thread.currentThread().getName() event);throw new RuntimeException(制造异常);}BeanExecutor taskExecutor() {return Executors.newSingleThreadExecutor();}
}Spirng 事件/监听实现原理 ListenerRetriever 会过滤对应的ApplicationListener Event实例 这个Event实例包括它本身及它的孙子类 处理泛型并过滤 在处理事件的时候就会去获取对应的监听器 参考资料小马哥核心编程思想。
