看項目代碼時遇到了好多事件監聽機制相關的代碼。現學習一下：

java事件機制包含三個部分：事件、事件監聽器、事件源。

1.事件：繼承自java.util.EventObject類，開發人員自己定義。

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.事件監聽器：實現java.util.EventListener接口,註冊在事件源上,當事件源的屬性或狀態改變時,取得對應的監聽器調用其內部的回調方法。

package com.shuyan.javatest.EventTest;

import java.util.EventListener;

public interface DnsEventListener extends EventListener {

    public void processDnsEvent(DnsEvent dnsEvent);

}

public class DnsEventaListenerImpl implements DnsEventListener {

    @Override
    public void processDnsEvent(DnsEvent dnsEvent) {

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

    }
}

3.事件源：事件發生的地方，因為事件源的某項屬性或狀態發生了改變導致某項事件發生。因為事件監聽器要註冊在事件源上,所以事件源類中應該要有盛裝監聽器的容器(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);
        }
    }


}

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

Java 中的事件監聽機制