Java 中的事件监听机制

看项目代码时遇到了好多事件监听机制相关的代码，现学习一下：

java事件机制包括三个部分：事件、事件监听器、事件源。

1.事件：继承自java.util.EventObject类，开发者自定义。

package com.shuyan.javatest.EventTest;

import java.util.EventObject;

public class DnsEvent extends EventObject {

private String userData;

private long parseTime;

public DnsEvent(Object source) {
super(source);
}

public DnsEvent(Object source, String userData, long parseTime) {
super(source);
this.userData = userData;
this.parseTime = parseTime;
}

public String getUserData() {
return userData;
}

public void setUserData(String userData) {
this.userData = userData;
}

public long getParseTime() {
return parseTime;
}

public void setParseTime(long parseTime) {
this.parseTime = parseTime;
}

}

2.事件监听器：实现java.util.EventListener接口,注册在事件源上,当事件源的属性或状态改变时,取得相应的监听器调用其内部的回调方法。

package com.shuyan.javatest.EventTest;

import java.util.EventListener;

public interface DnsEventListener extends EventListener {

public void processDnsEvent(DnsEvent dnsEvent);

}

监听器的具体实现类

public class DnsEventaListenerImpl implements DnsEventListener {

@Override
public void processDnsEvent(DnsEvent dnsEvent) {

String userdata = dnsEvent.getUserData();
System.out.println("userdata-->" + userdata);

}
}

3.事件源：事件发生的地方，由于事件源的某项属性或状态发生了改变导致某项事件发生。由于事件监听器要注册在事件源上,所以事件源类中应该要有盛装监听器的容器(List,Set等)。

public class ManagerListener {

private List<DnsEventListener> listeners = null;

private static class Singleton {
static ManagerListener managerListener = new ManagerListener();
}

public static ManagerListener getInstance() {
return Singleton.managerListener;
}

private ManagerListener() {
listeners = new ArrayList<>();
}

public void addDnsEventListener(DnsEventListener listener) {
this.listeners.add(listener);
}

public void removeDnsEventListener(DnsEventListener listener) {
this.listeners.remove(listener);
}

public void fireDnsEventListener(DnsEvent event) {
for (DnsEventListener listener : listeners) {
listener.processDnsEvent(event);
}
}

}

测试如下：

public class DnsEventTest {
public static void main(String[] args) {
ManagerListener managerListener = ManagerListener.getInstance();
DnsEvent dnsEvent = new DnsEvent(managerListener, "data", 1000L);
DnsEventaListenerImpl listener = new DnsEventaListenerImpl();

managerListener.addDnsEventListener(listener);
managerListener.fireDnsEventListener(dnsEvent);
}
}

参考：http://blog.csdn.net/longlong3050/article/details/6854456