BListener：

package demoListener;

import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;
import javax.servlet.annotation.WebListener;

@WebListener
public class BListener implements ServletContextAttributeListener {

    public void attributeAdded(ServletContextAttributeEvent scae)  { 
        System.out.println("你正在添加一个名为：" + scae.getName() + "，值为：" + scae.getValue() + "的属性内容");
    }
    public void attributeRemoved(ServletContextAttributeEvent scae)  { 
        System.out.println("你正在删除一个名为：" + scae.getName() + "，值为：" + scae.getValue() + "的属性内容");
    }
    public void attributeReplaced(ServletContextAttributeEvent scae)  { 
        System.out.println("你正在修改一个名为：" + scae.getName() + "，值为：" + scae.getValue() + "的属性内容");
    }
}

创建一个JSP页面：

index.jsp：

<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>title</title>
</head>
<body>
<%
    application.setAttribute("张三", 15);
    application.setAttribute("张三", 14);
    application.removeAttribute("张三");
    
%>
<h1>欢迎来到我的世界</h1>
</body>
</html>