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java使用監(jiān)聽器實(shí)現(xiàn)一個(gè)統(tǒng)計(jì)網(wǎng)站在線人數(shù)的示例

更新時(shí)間：2016年10月21日 09:29:55 作者：碧天云月

本文主要介紹了java使用監(jiān)聽器實(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ServletContextListener監(jiān)聽，當(dāng)Web應(yīng)用上下文啟動(dòng)時(shí)，在ServletContext中添加一個(gè)List，用來準(zhǔn)備存放在線的用戶名；然后，可以通過HttpSessionAttributeListener監(jiān)聽，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HttpSessionListener監(jiān)聽，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OnLineListener類實(shí)現(xiàn)ServletContextListener、HttpSessionAttributeListener、HttpSessionListener接口，具體代碼如下：

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中注冊監(jiān)聽器

監(jiān)聽器實(shí)現(xiàn)好后，還需要在web.xml文件中進(jìn)行注冊才能起作用，只需要在web.xml中像如下添加元素即可

<!-- 注冊一個(gè)監(jiān)聽器 -->
 <listener>
 <!-- 指定監(jiān)聽器實(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來測試這個(gè)監(jiān)聽器實(shí)現(xiàn)的功能。

處理用戶登錄的Servlet類代碼：

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: 要對鏈接URL進(jìn)行自動(dòng)重寫處理 
  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

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</a>"); 
  out.println(" </BODY>"); 
  out.println("</HTML>"); 
  out.flush(); 
  out.close(); 
 } 
}

然后創(chuàng)建一個(gè)index.html文件，用來供用戶登錄，代碼如下：

<!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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