Java怎么实现监听者模式(java,开发技术)

代码展示

Main：测试类

ObServer：每个被监听的对象实现该接口，重写该方法，完成自己的业务

publicinterfaceObServer{/***当某一个被监控的对象发生变化时*所有实现该方法处理方法*/voidexceptionHandler();}

Subject：监听者容器

publicinterfaceSubject{/***添加被观察对象*/voidadd(ObServerobServer);/***通知所有被观察者完成自己的exceptionHandler方法*/voidnotifyAllSubject();}

SubjectHandler：监听者容器的实现类

publicclassSubjectHandlerimplementsSubject{/***存放被监听对象*/privatestaticfinalList<ObServer>SUBJECTS=Collections.synchronizedList(newLinkedList<>());@Overridepublicvoidadd(ObServersubject){SUBJECTS.add(subject);}@OverridepublicvoidnotifyAllSubject(){SUBJECTS.forEach(ObServer::exceptionHandler);}}

Thread1、Thread2 测试对象

模拟两个线程对数据库操作，若Threa1执行时出异常了，那么终止所有线程并对其回滚。

Threa1:

publicclassThread1implementsObServer,Runnable{@SneakyThrows@Overridepublicvoidrun(){System.out.println("thread1run");Thread.sleep(1000);System.out.println("t1end");}@SneakyThrows@OverridepublicvoidexceptionHandler(){System.out.println("thread1rollback.....");}}

Thread2:

publicclassThread2implementsObServer,Runnable{privatestaticThreadCURRENT_THREAD;privatestaticvolatilebooleanFLAG=false;@SneakyThrows@Overridepublicvoidrun(){CURRENT_THREAD=Thread.currentThread();System.out.println("thread2running");intcount=0;while(!FLAG){System.out.println(count);count++;}System.out.println("thread2end");}@SneakyThrows@OverridepublicvoidexceptionHandler(){FLAG=true;CURRENT_THREAD.interrupt();System.out.println("thread2rollback.....");}}

测试Demo

publicstaticvoidmain(String[]args)throwsInterruptedException{//创建监听容器Subjectsubject=newSubjectHandler();Thread1thread1=newThread1();Thread2thread2=newThread2();subject.add(thread1);subject.add(thread2);CompletableFuture.supplyAsync(()->{newThread(thread1).start();try{Thread.sleep(10);inta=1/0;//模拟线程1报错}catch(InterruptedExceptione){e.printStackTrace();}returntrue;}).exceptionally((error)->{subject.notifyAllSubject();returnfalse;});CompletableFuture.supplyAsync(()->{newThread(thread2).start();returntrue;}).exceptionally((error)->{subject.notifyAllSubject();returnfalse;});//mainthreadawaitThread.sleep(60*1000);}

测试结果

在 java.util 包下提供了Observable（监听容器）和 Observer接口（被监听者），用法跟我们完全一致，只需实现Observer的update方法，把每个Observer子类添加到监听容器中。

注意：在调用监听容器的通知所有servers时首先调用一下其setChanged方法

将changed变为true（默认flase）