本文实例讲述了Java基于servlet监听器实现在线人数监控功能的方法。分享给大家供大家参考,具体如下:
1、分析:
做一个网站在线人数统计,可以通过ServletContextListener监听,当Web应用上下文启动时,在ServletContext中添加一个List.用来准备存放在线的用户名,然后通过HttpSessionAttributeListener监听,当用户登录成功,把用户名设置到Session中。同时将用户名方法到ServletContext的List中,最后通过HttpSessionListener监听,当用户注销会话时,讲用户名从应用上下文范围中的List列表中删除。
2、注意事项
测试时,需要启动不同的浏览器来登陆不同的用户,只有点击注销按钮才能减少在线用户,关闭浏览器不能减少在线用户。
3、项目源代码
(1)java代码
OnlineListener类
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package com.smalle.listener; import java.util.LinkedList; import java.util.List; 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 OnlineListener implements ServletContextListener, HttpSessionAttributeListener, HttpSessionListener { private ServletContext application = null ; //应用上下文初始时会回调的方法 @Override public void contextInitialized(ServletContextEvent e) { //初始化一个application对象 application = e.getServletContext(); //设置一个列表属性,用于保存在线用户名 this .application.setAttribute( "online" , new LinkedList<String>()); } //往会话中添加属性时的回调方法 @Override public void attributeAdded(HttpSessionBindingEvent e) { //取得用户名列表 List<String> onlines = (List<String>) this .application.getAttribute( "online" ); if ( "username" .equals(e.getName())){ onlines.add((String) e.getValue()); } //将添加后的列表重新设置列application属性中. this .application.setAttribute( "online" , onlines); } //会话销毁时会回调的方法 @Override public void sessionDestroyed(HttpSessionEvent e) { //取得用户名列表 List<String> onlines = (List<String>) this .application.getAttribute( "online" ); //取得当前用户名 String username = (String) e.getSession().getAttribute( "username" ); //将此用户从列表中删除 onlines.remove(username); //讲删除后的列表重新设置到application属性中. this .application.setAttribute( "online" , onlines); } public void sessionCreated(HttpSessionEvent e) {} public void attributeRemoved(HttpSessionBindingEvent e) {} public void attributeReplaced(HttpSessionBindingEvent e) {} public void contextDestroyed(ServletContextEvent e) {} } |
LoginServlet类
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package com.smalle.listener; import java.io.IOException; import java.io.PrintWriter; import java.util.List; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class LoginServlet extends HttpServlet { private static final long serialVersionUID = 1L; public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this .doPost(request, response); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding( "utf-8" ); //设置响应内容类型 String username= request.getParameter( "username" ); //获取请求参数中的用户名 //往session中添加属性,会触发HttpSessionAttributeListener中的attributeAdded方法 if (username != null && !username.equals( "" )) { request.getSession().setAttribute( "username" ,username); } //从应用上下文中获取在线用户名列表 List<String> online = (List<String>)getServletContext().getAttribute( "online" ); System.out.println( "LoginServlet" + online); response.setContentType( "text/html;charset=utf-8" ); PrintWriter out = response.getWriter(); out.println( "" ); out.println( " <title>用户列表</title>" ); out.println( " " ); out.println( "当前用户是:" + username); out.print( " <hr><h3>在线用户列表</h3>" ); int size = online == null ? 0 : online.size(); for ( int i = 0 ; i < size; i++) { if (i > 0 ){ out.println( "<br>" ); } out.println(i + 1 + "." + online.get(i)); } //注意: 要对链接URL进行自动重写处理 out.println( "<hr/><a href=\"" + response.encodeURL( "logoutListener" ) + "\">注销</a>" ); out.println( " " ); out.println( "" ); out.flush(); out.close(); } } |
LogoutServlet类
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package com.smalle.listener; import java.io.IOException; import java.io.PrintWriter; import java.util.List; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class LogoutServlet extends HttpServlet{ public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this .doPost(request, response); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding( "utf-8" ); //设置响应内容类型 //销毁会话,会触发SessionLinstener中的sessionDestroyed方法 request.getSession().invalidate(); //从应用上下文中获取在线用户名列表 List<String> online = (List<String>)getServletContext().getAttribute( "online" ); response.setContentType( "text/html;charset=utf-8" ); PrintWriter out = response.getWriter(); out.println( "" ); out.println( " <title>用户列表</title>" ); out.println( " " ); out.print( " <h3>在线用户列表</h3>" ); int size = online == null ? 0 : online.size(); for ( int i = 0 ; i < size; i++) { if (i > 0 ){ out.println( "<br>" ); } out.println(i + 1 + "." + online.get(i)); } out.println( "<hr><a href='\'index.html\''>主页</a>" ); out.println( " " ); out.println( "" ); out.flush(); out.close(); } } |
(2)web.xml代码
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<? xml version = "1.0" encoding = "UTF-8" ?> < web-app xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance" xmlns = "http://java.sun.com/xml/ns/javaee" xsi:schemaLocation = "http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id = "WebApp_ID" version = "3.0" > < display-name >testServlet</ display-name > < listener > < listener-class >com.smalle.listener.OnlineListener</ listener-class > </ listener > < servlet > < servlet-name >LoginServlet</ servlet-name > < servlet-class >com.smalle.listener.LoginServlet</ servlet-class > </ servlet > < servlet-mapping > < servlet-name >LoginServlet</ servlet-name > < url-pattern >/loginListener</ url-pattern > </ servlet-mapping > < servlet > < servlet-name >LogoutServlet</ servlet-name > < servlet-class >com.smalle.listener.LogoutServlet</ servlet-class > </ servlet > < servlet-mapping > < servlet-name >LogoutServlet</ servlet-name > < url-pattern >/logoutListener</ url-pattern > </ servlet-mapping > < welcome-file-list > < welcome-file >index.jsp</ welcome-file > </ welcome-file-list > </ web-app > |
(3)表现层代码
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<!DOCTYPE html> < html > < head > < title >index.html</ title > < meta name = "content-type" content = "text/html; charset=UTF-8" > </ head > < body > < form action = "loginListener" method = "post" > 用户名:< input type = "text" name = "username" > < input type = "submit" value = "登录" >< br >< br > </ form > </ body > </ html > |
希望本文所述对大家java程序设计有所帮助。
原文链接:http://blog.csdn.net/oldinaction/article/details/40622393