想研究 汤姆猫，发现里面很多监听器 : LifecycleEvent,Lifecycle,ServletContextListener(Spring)等，故作此文。

java在gui方面用到了大量该模式，当初上大学时用过swing，awt，现在全忘了。有兴趣的可以深究一下。

事件-监听器模式需要四个类：事件源，事件，监听器(interface)，具体的监听器

事件源产生事件，如窗口产生点击、关闭事件。

监听器是具体监听器的抽象，面向接口的编程。事件源不需要知道监听器的具体实现细节，只需调用抽要即可。

jdk已有该模式的规范，

//监听器接口package java.util;public interface EventListener {}//事件package java.util;/** * 
 * The root class from which all event state objects shall be derived. * 
 * All Events are constructed with a reference to the object, the "source", * that is logically deemed to be the object upon which the Event in question * initially occurred upon. * * @since JDK1.1 */public class EventObject implements java.io.Serializable {    private static final long serialVersionUID = 5516075349620653480L;    /**     * The object on which the Event initially occurred.     */    protected transient Object  source;    /**     * Constructs a prototypical Event.     *     * @param    source    The object on which the Event initially occurred.     * @exception  IllegalArgumentException  if source is null.     */    public EventObject(Object source) {        if (source == null)            throw new IllegalArgumentException("null source");        this.source = source;    }    /**     * The object on which the Event initially occurred.     *     * @return   The object on which the Event initially occurred.     */    public Object getSource() {        return source;    }    /**     * Returns a String representation of this EventObject.     *     * @return  A a String representation of this EventObject.     */    public String toString() {        return getClass().getName() + "[source=" + source + "]";    }}

这个监听器是个空接口，我们可以自己定义一个EventList接口，包含一个void onEvent(ConcreateEventObject  eventObject)方法。

本文头部的链接写的很好，读者可以点进去细读。thanks