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事件机制包含三个部分：事件、事件监听器、事件源。

1.事件：继承自java.util.EventObject类，开发人员自己定义。

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 = http://www.mamicode.com/userData;>
2.事件监听器：实现java.util.EventListener接口,注冊在事件源上,当事件源的属性或状态改变时,取得对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);

}
监听器的详细实现类
public class DnsEventaListenerImpl implements DnsEventListener {

    @Override
    public void processDnsEvent(DnsEvent dnsEvent) {

        String userdata = http://www.mamicode.com/dnsEvent.getUserData();>
3.事件源：事件发生的地方，因为事件源的某项属性或状态发生了改变导致某项事件发生。因为事件监听器要注冊在事件源上,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);
        }
    }


}
測试例如以下：

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);
    }
}



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