计数在servlet的

Question

在web应用程序的用户数我已经修改我的应用程序，找出用户的数量记录在一个Web应用程序下面是我的代码..

监听器类

import javax.servlet.ServletContext; 
import javax.servlet.http.HttpSessionEvent; 
import javax.servlet.http.HttpSessionListener; 


public class SessionCounter implements HttpSessionListener 
{ 
     private static int count; 

     public static int getActiveSessions() { 
      return count; 
      } 



     public SessionCounter() 
     { 
     } 

//The "sessionCount" attribute which has been set in the servletContext should not be modified in any other part of the application. 
//Since we are using serveltContext in both the methods to modify the same variable, we have synchronized it for consistency. 


     public void sessionCreated(HttpSessionEvent e) 
     { 
       count++; 
       ServletContext sContext = e.getSession().getServletContext(); 
       synchronized (sContext) 
       { 
         sContext.setAttribute("sessionCount", new Integer(count)); 
       } 
     } 

     public void sessionDestroyed(HttpSessionEvent e) 
     { 
       count--; 
       ServletContext sContext = e.getSession().getServletContext(); 
       synchronized (sContext) 
       { 
         sContext.setAttribute("sessionCount", new Integer(count)); 
       } 
     } 
} 

和主要的servlet ..

package com.saral; 

import java.io.IOException; 
import org.apache.log4j.Logger; 
import org.apache.log4j.PropertyConfigurator; 
import java.io.PrintWriter; 

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

/** 
* Servlet implementation class First 
*/ 
//@WebServlet("/First") 
public class MyServlet extends HttpServlet 
{ 
    private static final long serialVersionUID = 1L; 
    static final Logger logger = Logger.getLogger(MyServlet.class); 


    /** 
    * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 
    */ 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
     PropertyConfigurator.configure("log4j.properties"); 
     logger.info("before---->"); 

     // TODO Auto-generated method stub 
     String name=request.getParameter("txtName"); 
     response.setContentType("text/html"); 
     PrintWriter out=response.getWriter(); 
     out.println("Hello,"+name); 
     out.println("<br> this output is generated by a simple servlet."); 
     out.println("Total Number of users logged in--->"+SessionCounter.getActiveSessions()); 
     out.close(); 


    } 

} 

和web.xml中是...

<?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" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" 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>FirstDemo</display-name> 


    <context-param> 
     <param-name>log4jConfigLocation</param-name> 
     <param-value>/WEB-INF/log4j.properties</param-value> 
</context-param> 


    <servlet> 
    <servlet-name>hello</servlet-name> 
    <servlet-class>com.saral.MyServlet</servlet-class> 
    </servlet> 
    <servlet-mapping> 
    <servlet-name>hello</servlet-name> 
    <url-pattern>/helloServlet</url-pattern> 
    </servlet-mapping> 
    <welcome-file-list> 
    <welcome-file>home.html</welcome-file> 
    </welcome-file-list> 


    <listener> 
    <listener-class>com.saral.SessionCounter</listener-class> 
</listener> 

</web-app> 

但我获得的登录用户总数为0，这并不完美，请告知我错在哪里以及如何克服这一点。

Answer 1

当客户端请求到达Tomcat服务器并且您没有调用request.getSession()时，那么Tomcat服务器stil会自动创建一个会话。之后，调用SessionCounter类中的方法sessionCreated(...)。

当会话被销毁时，方法sessionDestroyed(...)将被调用。当您拨打session.invalidate()时会发生这种情况。如果关闭浏览器上的选项卡或关闭浏览器，则会话在您的tomcat服务器上仍然存在。

我这么认为。你可以使用一些不同势听众归档你的目标：HttpSessionAttributeListener，HttpSessionBindingListener，...