监听器(使用HttpSessionListener实现在线人数统计)

最新推荐文章于 2025-03-29 10:47:59 发布

CarlosXu14

最新推荐文章于 2025-03-29 10:47:59 发布

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分类专栏：编程语言

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介绍
监听器是一个专门用于对其他对象身上发生的事件或状态改变进行监听和相应处理的对象，当被监视的对象发生情况时，立即采取相应的行动。监听器其实就是一个实现特定接口的普通java程序，这个程序专门用于监听另一个java对象的方法调用或属性改变，当被监听对象发生上述事件后，监听器某个方法立即被执行。
案列(使用HttpSessionListener实现在线人数统计)

package com.ListenerServlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class TestDemo implements ServletContextListener,HttpSessionListener,HttpSessionAttributeListener{
	
	private ServletContext servletContext=null;
	
	@Override
	public void attributeAdded(HttpSessionBindingEvent session) {
		// TODO Auto-generated method stub
		servletContext = session.getSession().getServletContext();
		if(session.getName().equals("name")){
			int attribute = (int) servletContext.getAttribute("count");
			++attribute;
			System.out.println(attribute+"===========");
			servletContext.setAttribute("count", attribute);
		}
	}

	@Override
	public void sessionDestroyed(HttpSessionEvent session) {
		// TODO Auto-generated method stub
		servletContext = session.getSession().getServletContext();
		int attribute = (int) servletContext.getAttribute("count");
		--attribute;
		System.out.println(attribute+"===========");
		servletContext.setAttribute("count", attribute);
	}

	@Override
	public void contextDestroyed(ServletContextEvent app) {
		// TODO Auto-generated method stub
		}

	@Override
	public void contextInitialized(ServletContextEvent app) {
		// TODO Auto-generated method stub
		int count=0;
		servletContext = app.getServletContext();
		servletContext.setAttribute("count", count);
	}


	@Override
	public void attributeRemoved(HttpSessionBindingEvent arg0) {
		// TODO Auto-generated method stub
		
	}


	@Override
	public void attributeReplaced(HttpSessionBindingEvent arg0) {
		// TODO Auto-generated method stub
		
	}


	@Override
	public void sessionCreated(HttpSessionEvent arg0) {
		// TODO Auto-generated method stub
		
	}

}

package com.Controller;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

@WebServlet("/LoginController")
public class LoginController extends HttpServlet {

	
	@Override
	public void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// TODO Auto-generated method stub
		String name=req.getParameter("name");
		HttpSession session=req.getSession();
		session.setAttribute("name", name);
		req.getRequestDispatcher("index.jsp").forward(req, resp);
	}
	
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// TODO Auto-generated method stub
		HttpSession session1=req.getSession();
		String attribute = (String) session1.getAttribute("name");
		session1.invalidate();
	}
}

<%@ 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>

${applicationScope.count}
${sessionScope.name}

<!--
<%
session.invalidate();
%>
-->
<a href="LoginController"><button>注销</button></a>
</body>
</html>