Java监听：一个Java睡前故事(Java Listener: A Java Bedtime Sto

Java监听：一个Java睡前故事(Java Listener: A Java Bedtime Story)

作者: 杨帆 博 邮

本文是仿照 .NET Delegates: A C# Bedtime Story 的功能实现的Java版源代码，时间原因，没有给出文字故事

接口定义

package cn.steven.demo;import java.util.EventListener;import java.util.EventObject;/** * 监听接口 用于处理各种事件 * 此处设计与JDK不同 */public interface StevenEventListener extends EventListener {public void doListen(EventObject e);}package cn.steven.demo;/** * 评价接口 */public interface IAppraisable {//评价的方法public void appraise(String name, int degree);}

事件

独立工作事件

package cn.steven.demo;import java.util.EventObject;public class WorkEvent extends EventObject {private String eventMsg = "干活了";public String getEventMsg() {return eventMsg;}public void setEventMsg(String eventMsg) {this.eventMsg = eventMsg;}/** * 自动升成的serialVersionUID用于序列化 */private static final long serialVersionUID = 6232430258434094316L;/** * @param source 事件源 */public WorkEvent(Object source) {super(source);}}

生活事件 (注意此事件有两个子类)

package cn.steven.demo;import java.util.EventObject;public abstract class LifeEvent extends EventObject {public abstract String getEventMsg();public LifeEvent(Object source) {super(source);}private static final long serialVersionUID = -5117554641874171524L;}

package cn.steven.demo;public class BornEvent extends LifeEvent {private String eventMsg = "出生";public String getEventMsg() {return eventMsg;}public void setEventMsg(String eventMsg) {this.eventMsg = eventMsg;}public BornEvent(Object source) {super(source);}private static final long serialVersionUID = 8880371520168303175L;}

package cn.steven.demo;public class DieEvent extends LifeEvent {public DieEvent(Object source) {super(source);}private String eventMsg = "死亡";public String getEventMsg() {return eventMsg;}public void setEventMsg(String eventMsg) {this.eventMsg = eventMsg;}private static final long serialVersionUID = 5643693360168396103L;}

监听器

package cn.steven.demo;import java.util.EventObject;public class Boss implements StevenEventListener{/** * 只对WorkEvent事件响应 */@Overridepublic void doListen(EventObject e) {if(e instanceof WorkEvent){System.out.println("老板:"+e.getSource()+"开工啦!");try {//老板由于事务繁忙，打分时间要长，所以需要异步调用节省时间Thread.currentThread().sleep(500);} catch (InterruptedException e1) {}Object source = e.getSource();//如果可以打分if(source instanceof IAppraisable){IAppraisable ia = (IAppraisable)source;//老板打分ia.appraise("老板", 5);}}}}package cn.steven.demo;import java.util.EventObject;public class God implements StevenEventListener {@Overridepublic void doListen(EventObject e) {if (e instanceof LifeEvent) {LifeEvent de = (LifeEvent) e;System.out.println("上帝：(生命时间)" + de.getSource() + de.getEventMsg());}if (e instanceof WorkEvent) {WorkEvent de = (WorkEvent) e;System.out.println("上帝：(工作时间)" + de.getSource() + de.getEventMsg());try {//god由于事务繁忙，打分时间要长，所以需要异步调用节省时间Thread.currentThread().sleep(1000);} catch (InterruptedException e1) {}Object source = e.getSource();//如果可以打分if(source instanceof IAppraisable){IAppraisable ia = (IAppraisable)source;//上帝打分ia.appraise("上帝", 6);}}}}package cn.steven.demo;import java.util.EventObject;public class Satan implements StevenEventListener {@Overridepublic void doListen(EventObject e) {if (e instanceof DieEvent) {DieEvent de = (DieEvent) e;System.out.println("撒旦：" + de.getSource() + de.getEventMsg());}}}

事件源

package cn.steven.demo;import java.util.EventObject;import java.util.HashMap;import java.util.LinkedList;import java.util.List;import java.util.Map;//Worker的工作是可以评价的IAppraisablepublic class Worker implements IAppraisable {private String name;private Map<Class<? extends EventObject>, List<StevenEventListener>> listenerMap;public Worker(String name) {this.name = name;listenerMap = new HashMap<Class<? extends EventObject>, List<StevenEventListener>>();}@Overridepublic String toString() {return name;}// 增加监听器public synchronized void addListener(StevenEventListener listener,Class<? extends EventObject>… eventClass) {if (null != listenerMap) {if (eventClass.length <= 0) {throw new RuntimeException("至少指定一个事件进行监听！");} else {for (int i = 0; i < eventClass.length; i++) {Class<? extends EventObject> e = eventClass[i];List<StevenEventListener> list = null;if (listenerMap.containsKey(e)) {list = listenerMap.get(e);}if (null == list) {list = new LinkedList<StevenEventListener>();}if (list.contains(listener)) {// 如果已存在，不操作，处理下一个事件continue;}list.add(listener);listenerMap.put(e, list);}}}}// 移除事件监听器public synchronized void removeEventListener(StevenEventListener listener,Class<? extends EventObject>… eventClass) {if (null != listenerMap) {// 如果没给定第二个参数if (eventClass.length <= 0) {// 在所有事件中移除监听器for (Map.Entry<Class<? extends EventObject>, List<StevenEventListener>> entry : listenerMap.entrySet()) {List<StevenEventListener> list = entry.getValue();if (null != list) {list.remove(listener);}}} else {// 在给定的事件中移除监听器for (int i = 0; i < eventClass.length; i++) {Class<? extends EventObject> e = eventClass[i];if (listenerMap.containsKey(e)) {List<StevenEventListener> list = listenerMap.get(e);if (null != list) {list.remove(listener);}}}}}}public synchronized void removeListener(StevenEventListener listener) {if (null != listenerMap) {}}// 移除所有监听器public synchronized void removeAllListener() {if (null != listenerMap) {listenerMap.clear();}}// 处理监听public void doEvent(final EventObject e) {if (null != listenerMap) {// 在此，如果key是event的祖先也可以监听for (Map.Entry<Class<? extends EventObject>, List<StevenEventListener>> entry : listenerMap.entrySet()) {if (entry.getKey().isInstance(e)) {if (null != entry.getValue()) {for (final StevenEventListener stevenEventListener : entry.getValue()) {if (null != stevenEventListener) {// 处理监听 同步方法// stevenEventListener.doListen(e);// 处理监听 异步多线程方法Thread t = new Thread(new Runnable() {public void run() {stevenEventListener.doListen(e);}});// 如果设置为守护进程，程序退出后此进程关闭// t.setDaemon(true);// 如果不设置为守护，则程序退出后线程还会运行t.start();// 如果想再次等待非守护想成结束在结束进程(阻塞调用线程，直到某个线程终止时为止。变为同步)，则join// try {// t.join();//必须放在线程启动的后面// } catch (InterruptedException e1) {// }}}}}}}}// 工作方法public void work() {System.out.println("@我干活了!");doEvent(new WorkEvent(this));}public void born() {System.out.println("@我出生了!");doEvent(new BornEvent(this));}public void die() {System.out.println("@我死了!");doEvent(new DieEvent(this));}//对工作打分 需要回调(callback)@Overridepublic void appraise(String name, int degree){System.out.println(name+"评价工作为"+degree+"分!");}}

运行

package cn.steven.demo;public class Run {public static void main(String[] args) {System.out.println("/t进程开始");// 事件源Worker worker = new Worker("东方不败");Boss boss = new Boss();God god = new God();Satan satan = new Satan();// 老板只对工作关心worker.addListener(boss, WorkEvent.class);// god对两种时间都关心worker.addListener(god, WorkEvent.class, LifeEvent.class);// satan对死亡关心worker.addListener(satan, DieEvent.class);worker.work();worker.born();worker.die();System.out.println("/t进程结束 在此后出现的为非守护线程");}}

运行结果

进程开始@我干活了!@我出生了!老板:东方不败开工啦!@我死了!上帝：(工作时间)东方不败干活了上帝：(生命时间)东方不败出生进程结束 在此后出现的为非守护线程撒旦：东方不败死亡上帝：(生命时间)东方不败死亡老板评价工作为5分!上帝评价工作为6分!

后记

java版的故事很明显要比c#的代码多，这实际上是由于Java中的很多机制是编程实现而不是类库和语言特性支持的缘故，下图是两种实现的比较。

javac#说明效率采用多态，相对高采用委托，相对低。应该说，它们都是在运行时获取对哪个对象的哪个方法进行调用，但是采用多态相对于委托效率高一点。是否支持静态方法调用否是java采用多态，当然不能把方法声明为static;c#中delegate中的_object可以为null来实现对静态方法的调用是否类型安全是是它们都会在编译时对响应函数进行参数检查，类型安全。开发者易用性两级实体对象：事件源-与事件响应者三级实体对象：事件源-委托-事件响应者由于有delegate的封装，不用编写事件注册/注销之类的代码，c#事件处理易用性相对高；注意，虽然java中采用接口来规范响应函数，但这里却说java中是两级实体对象，是因为在运行时并不存在接口的实例(实际上，接口也不可实例化，呵呵)

也会有想更换的念头。旅行，正好提供了这样一个机会，