监听器

一 监听器作用
主要是用来监听特定对象的创建对象或销毁，属性的变化的！是一个实现特定接口的普通java类。
Servlet中哪些对象需要监听？
request/session/servletContext
分别对应的request监听器，session相关监听器，servletContext监听器
二 监听器（listener）概述
监听器接口

• 监听器对象创建/销毁的监听器接口
  Interface ServletRequestListener 监听request对象的创建或销毁
  Interface HttpSessionListener 监听session对象的创建或销毁
  Interface ServletContextListener 监听servletContext对象的创建或销毁
• 监听对象属性的变化
  Interface ServletRequestAttributeListener 监听request对象属性变化: 添加、移除、修改
  Interface HttpSessionAttributeListener 监听session对象属性变化: 添加、移除、修改
  Interface ServletContextAttributeListener 监听servletContext对象属性变化
• session相关监听器
  Interface HttpSessionBindingListener 监听对象绑定到session上的事件
  Interface HttpSessionActivationListener(了解) 监听session序列化及反序列化的事件
  三 程序实现
  1 生命周期监听
  index.jsp

<%--
  Created by IntelliJ IDEA.
  User: pc
  Date: 2017/9/6
  Time: 17:48
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    


欢迎访问index页面
<%
    request.setAttribute("name","Yang");
%>

RequestListener.java

package entity;

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

/**
 * Created by pc on 2017/9/12.
 */
public class RequestListener implements ServletRequestListener {
    public void requestDestroyed(ServletRequestEvent servletRequestEvent) {
       Object object = servletRequestEvent.getServletRequest().getAttribute("name");
        System.out.println("2.对象销毁"+object);
    }

    public void requestInitialized(ServletRequestEvent servletRequestEvent) {
        Object object1 = servletRequestEvent.getServletRequest().getAttribute("name");
        System.out.println("1.对象创建"+object1);
    }
}

.xml配置

  Archetype Created Web Application

  entity.RequestListener

测试结果

2 属性监听（监听session变化）
index.jsp

<%--
  Created by IntelliJ IDEA.
  User: pc
  Date: 2017/9/6
  Time: 17:48
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    


欢迎访问index页面
<%
    session.setAttribute("name","YY");
    session.removeAttribute("name");
%>

SessionAttributeListener.java

package entity;
import javax.servlet.http.*;

/**
 * Created by pc on 2017/9/12.
 */
public class SessionAttributeListener implements HttpSessionAttributeListener {

    public void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {
        System.out.println("创建session");
    }

    public void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {
        System.out.println("移除session");
    }

    public void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) {
        System.out.println("修改session");
    }
}

.xml配置

  Archetype Created Web Application
  
    entity.SessionAttributeListener
  

运行结果