本文主要介紹了java使用監(jiān)聽(tīng)器實(shí)現(xiàn)一個(gè)統(tǒng)計(jì)網(wǎng)站在線人數(shù)的示例，具有一定的參考價(jià)值，有需要的朋友可以了解一下。
（1）創(chuàng)建一個(gè)監(jiān)聽(tīng)器實(shí)現(xiàn)類
要大致統(tǒng)計(jì)一個(gè)網(wǎng)站的在線人數(shù)，首先，可以通過(guò)ServletContextListener監(jiān)聽(tīng)，當(dāng)Web應(yīng)用上下文啟動(dòng)時(shí)，在ServletContext中添加一個(gè)List，用來(lái)準(zhǔn)備存放在線的用戶名；然后，可以通過(guò)HttpSessionAttributeListener監(jiān)聽(tīng)，當(dāng)用戶登錄成功把用戶名設(shè)置到Session中時(shí)同時(shí)將用戶名存放到ServletContext中的List列表中；最后通過(guò)HttpSessionListener監(jiān)聽(tīng)，當(dāng)用戶注銷會(huì)話時(shí)將用戶名從應(yīng)用上下文范圍中的List列表中刪除。
所以，編寫(xiě)OnLineListener類實(shí)現(xiàn)ServletContextListener、HttpSessionAttributeListener、HttpSessionListener接口，具體代碼如下：
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package com.web.servlet; 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; //在線人數(shù)統(tǒng)計(jì)監(jiān)聽(tīng)器實(shí)現(xiàn)類 public class OnlineListener implements ServletContextListener, HttpSessionAttributeListener, HttpSessionListener { private ServletContext application = null; public void contextDestroyed(ServletContextEvent arg0) { // TODO Auto-generated method stub } public void contextInitialized(ServletContextEvent arg0) { //初始化一個(gè)application對(duì)象 this.application = arg0.getServletContext(); //設(shè)置一個(gè)列表屬性，用于保存在想用戶名 this.application.setAttribute("online", new LinkedList<String>()); } //往會(huì)話中添加屬性時(shí)會(huì)回調(diào)的方法 public void attributeAdded(HttpSessionBindingEvent arg0) { //取得用戶名列表 List<String> online = (List<String>) this.application .getAttribute("online"); if ("username".equals(arg0.getName())) { //將當(dāng)前用戶名添加到列表中 online.add((String) arg0.getValue()); } //將添加后的列表重新設(shè)置到application屬性中 this.application.setAttribute("online", online); } public void attributeRemoved(HttpSessionBindingEvent arg0) { // TODO Auto-generated method stub } public void attributeReplaced(HttpSessionBindingEvent arg0) { // TODO Auto-generated method stub } public void sessionCreated(HttpSessionEvent arg0) { // TODO Auto-generated method stub } //會(huì)話銷毀時(shí)會(huì)回調(diào)的方法 public void sessionDestroyed(HttpSessionEvent arg0) { //取得用戶名列表 List<String> online = (List<String>) this.application .getAttribute("online"); //取得當(dāng)前用戶名 String username = (String) arg0.getSession().getAttribute("username"); //將此用戶名從列表中刪除 online.remove(username); //將刪除后的列表重新設(shè)置到application屬性中 this.application.setAttribute("online", online); } } |
（2）在web.xml中注冊(cè)監(jiān)聽(tīng)器
監(jiān)聽(tīng)器實(shí)現(xiàn)好后，還需要在web.xml文件中進(jìn)行注冊(cè)才能起作用，只需要在web.xml中像如下添加元素即可
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<!-- 注冊(cè)一個(gè)監(jiān)聽(tīng)器 --> <listener> <!-- 指定監(jiān)聽(tīng)器實(shí)現(xiàn)類的全限定名 --> <listener-class> com.web.servlet.OnlineListener </listener-class> </listener |
最后，我們創(chuàng)建幾個(gè)Servlet來(lái)測(cè)試這個(gè)監(jiān)聽(tīng)器實(shí)現(xiàn)的功能。
處理用戶登錄的Servlet類代碼：
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package com.web.servlet; 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; //處理用戶登錄的Servlet public class LoginServlet 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");//設(shè)置相應(yīng)內(nèi)容類型 String username= request.getParameter("username");//獲取請(qǐng)求參數(shù)中的用戶名 //往session中添加屬性,會(huì)觸發(fā)HttpSessionAttributeListener中的attributeAdded方法 if(username != null && !username.equals("")) { request.getSession().setAttribute("username",username); } //從應(yīng)用上下文中獲取在線用戶名列表 List<String> online = (List<String>)getServletContext().getAttribute("online"); response.setContentType("text/html;charset=utf-8"); PrintWriter out = response.getWriter(); out.println("<HTML>"); out.println(" <HEAD><TITLE>用戶列表</TITLE></HEAD>"); out.println(" <BODY>"); out.println("當(dāng)前用戶是：" + username); out.print(" <hr/><h3>在線用戶列表</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: 要對(duì)鏈接URL進(jìn)行自動(dòng)重寫(xiě)處理 out.println("<hr/><a href="/" mce_href="/""" + response.encodeURL("logout") + "/">注銷</a>"); out.println(" </BODY>"); out.println("</HTML>"); out.flush(); out.close(); } } |
處理用戶登錄Servlet的類代碼
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package com.web.servlet; import java.io.*; import java.util.List; import javax.servlet.ServletException; import javax.servlet.http.*; //處理用戶注銷會(huì)話的Servlet 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"); //銷毀會(huì)話,會(huì)觸發(fā)SessionLinstener中的sessionDestroyed方法 request.getSession().invalidate(); //從應(yīng)用上下文中獲取在線用戶名列表 List<String> online = (List<String>)getServletContext().getAttribute("online"); response.setContentType("text/html;charset=utf-8"); PrintWriter out = response.getWriter(); out.println("<HTML>"); out.println(" <HEAD><TITLE>用戶列表</TITLE></HEAD>"); out.println(" <BODY>"); out.print(" <h3>在線用戶列表</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="/" mce_href="/""index.html/">主頁(yè)</a>"); out.println(" </BODY>"); out.println("</HTML>"); out.flush(); out.close(); } } |
然后創(chuàng)建一個(gè)index.html文件，用來(lái)供用戶登錄，代碼如下：
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <title>index.html</title> </head> <body> <form action = "login" method = "post"> 用戶名：<input type ="text" name = "username"/> <input type = "submit" value = "登錄"/><br/><br/> </form> </body> </html> |
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