Web中的监听器【Listener】

package com.wangzhu.listener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

/**
 * Servlet监听器：Servlet规范中定义的一种特殊类，它用于监听Web应用程序中的ServletContext、<br/>
 * HttpSession和ServletRequest等域对象的创建与销毁事件，以及监听这些域对象中的属性发生修改的事件。<br/>
 * 
 * ServeltContextListener接口<br/>
 * 其用于监听ServletContext对象的创建和销毁事件。<br/>
 * 当ServletContext对象被创建时，激发contextInitialized(ServletContextEvent sce)方法<br/>
 * 当ServletContext对象被销毁时，激发contextDestroyed(ServletContextEvent sce)方法<br/>
 * 
 * Servlet的监听器Listener<br/>
 * 随Web应用的启动而启动，只初始化一次，并随Web应用的停止而销毁<br/>
 * 
 * @author wangzhu
 * @date 2015-2-1上午12:20:42
 * 
 */
public class MyServletContextListener implements ServletContextListener {

    /**
     * 应用监听器的初始化方法
     */
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        System.out.println("MyServletContextListener contextInitialized");
    }

    /**
     * 应用监听器的销毁方法
     */
    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        System.out.println("MyServletContextListener contextDestroyed");
    }

}

package com.wangzhu.listener;

import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

/**
 * HttpSessionListener接口<br/>
 * 其用于监听HttpSession对象的创建和销毁<br/>
 * 当创建一个Session时，激发sessionCreated(HttpSessionEvent se)方法<br/>
 * 当销毁一个Session时，激发sessionDestroyed(HttpSessionEvent se)方法<br/>
 * 
 * @author wangzhu
 * @date 2015-2-1下午3:48:10
 * 
 */
public class MyHttpSessionListener implements HttpSessionListener {

    @Override
    public void sessionCreated(HttpSessionEvent se) {
        System.out.println("MyHttpSessionListener sessionCreated");
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        System.out.println("MyHttpSessionListener sessionDestroyed");
    }

}

package com.wangzhu.listener;

import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;

/**
 * ServletRequestListener接口<br/>
 * 
 * 其用于监听ServletRequest对象的创建和销毁<br/>
 * 当创建一个ServletRequest时，激发requestInitialized(ServletRequestEvent sre)方法<br/>
 * 当销毁一个ServletRequest时，激发requestDestroyed(ServletRequestEvent sre)方法<br/>
 * 
 * @author wangzhu
 * @date 2015-2-1下午3:51:31
 * 
 */
public class MyServletRequestListener implements ServletRequestListener {

    @Override
    public void requestDestroyed(ServletRequestEvent sre) {
        System.out.println("MyServletRequestListener requestDestroyed");
    }

    @Override
    public void requestInitialized(ServletRequestEvent sre) {
        System.out.println("MyServletRequestListener requestInitialized");
    }

}

  
    <!--ServletContext监听器-->
    <listener>
        <listener-class>com.wangzhu.listener.MyServletContextListener</listener-class>
    </listener>
    
    <!--HttpSession监听器-->
    <listener>
        <listener-class>com.wangzhu.listener.MyHttpSessionListener</listener-class>
    </listener>
    
    <!--ServletRequest监听器-->
    <listener>
        <listener-class>com.wangzhu.listener.MyServletRequestListener</listener-class>
    </listener>