监听器 - 学习笔记

一.监听器作用：

主要是用来监听特定对象的创建或销毁、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
分别对应的是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.生命周期监听器

声明周期监听器： 监听对象的创建、销毁的过程！
监听器开发步骤：
1.写一个普通java类，实现相关接口；
2.配置(web.xml)

• 监听request对象的创建或者销毁

index.jsp

<%--
  Created by IntelliJ IDEA.
  User: 马欢欢
  Date: 2017/5/30
  Time: 10:52
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    


Hello World!
欢迎访问index页面
<%
    request.setAttribute("huan","mahuan");
%>

web.xml

  Archetype Created Web Application
  
  
    ed.huan.listener.RequestListener
  

RequestListener.java

package ed.huan.listener;

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

/**
 * Created by 马欢欢  on 17-6-1.
 */
public class RequestListener implements ServletRequestListener {
    //对象销毁
    public void requestDestroyed(ServletRequestEvent servletRequestEvent) {
        Object obj = servletRequestEvent.getServletRequest().getAttribute("huan");
        System.out.println("2.对象销毁"+obj);
    }
    //对象创建
    public void requestInitialized(ServletRequestEvent servletRequestEvent) {
        Object obj1 = servletRequestEvent.getServletRequest().getAttribute("huan");
        System.out.println("1.对象创建"+ obj1);
    }
}

2.属性监听

• 监听session属性的变化

index.jsp

<%--
  Created by IntelliJ IDEA.
  User: 马欢欢
  Date: 2017/5/30
  Time: 10:52
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    


Hello World!
欢迎访问index页面
<%
    session.setAttribute("huan","mahuan");
    session.removeAttribute("huan");

%>

web.xml

    ed.huan.listener.Session
  

SessionAttributeListener.java

package ed.huan.listener;

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

/**
 * Created by 马欢欢  on 17-6-1.
 */
public class RequestListener implements ServletRequestListener {
    //对象销毁
    public void requestDestroyed(ServletRequestEvent servletRequestEvent) {
        Object obj = servletRequestEvent.getServletRequest().getAttribute("huan");
        System.out.println("2.对象销毁"+obj);
    }
    //对象创建
    public void requestInitialized(ServletRequestEvent servletRequestEvent) {
        Object obj1 = servletRequestEvent.getServletRequest().getAttribute("huan");
        System.out.println("1.对象创建"+ obj1);
    }
}

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