Javaweb之再谈监听器

最新推荐文章于 2023-09-18 22:07:41 发布

原创最新推荐文章于 2023-09-18 22:07:41 发布 · 259 阅读

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#监听器

博客围绕HttpSessionBindingListener接口展开，介绍了让Student类实现该接口，准备SessionAttributeListener用于观察，还提及index.jsp、add.jsp、delete.jsp等页面。启动服务器访问index页面，点击添加和删除按钮，分别触发valueBound和valueUnbound方法。

HttpSessionBindingListener接口

Student类，实现了HttpSessionBindingListener接口；

package com.zzu.listener.vo;

import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;

public class Student implements HttpSessionBindingListener {//此监听器的作用是监听一个对象添加到session对象的过程

	private String id;
	private String name;
	
	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	@Override
	public void valueBound(HttpSessionBindingEvent event) {
		System.out.println(this+"Student对象已经添加到session中");
	}

	@Override
	public void valueUnbound(HttpSessionBindingEvent event) {
		System.out.println(this+"Student对象已经从session中删除");
	}

}

准备一个SessionAttributeListener方便观察；

package com.zzu.listener.attribute;

import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;

public class SessionAttributeListener implements HttpSessionAttributeListener {

	public SessionAttributeListener() {
		System.out.println("构造方法");
	}
	@Override
	public void attributeAdded(HttpSessionBindingEvent arg0) {
		System.out.println("添加");
	}

	@Override
	public void attributeRemoved(HttpSessionBindingEvent arg0) {
		System.out.println("删除");

	}

	@Override
	public void attributeReplaced(HttpSessionBindingEvent arg0) {
		System.out.println("替换");
	}

}

index.jsp

<%@page import="com.zzu.listener.vo.Student"%>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<a href="./add.jsp">添加</a>
<a href="./delete.jsp">删除</a>

</body>
</html>

add.jsp

<%@page import="com.zzu.listener.vo.Student"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<%
	Student student = new Student();
	session.setAttribute("student", student);
%>
</body>
</html>

delete.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<%
	session.removeAttribute("student");
%>
</body>
</html>

启动服务器，访问index页面
在这里插入图片描述
点击添加按钮，控制台输出结果为

com.zzu.listener.vo.Student@e4aa01Student对象已经添加到session中
添加

说明执行了执行了valueBound方法；

点击删除按钮，控制台输出结果为

com.zzu.listener.vo.Student@e4aa01Student对象已经从session中删除
删除

说明执行了valueUnbound方法；