java web用监听器listener简单的实现在线统计人数

今天又重新学习了java web的基础 监听器技术，用sessionListener简单的实现了网页统计在线人数 （有一个bug就是当关闭网页的时候 session不会关闭依旧存在，除非关闭服务器），代码如下(前端网页代码就不显示了):

LoginServlet.java:

 1 import javax.servlet.ServletException;
 2 import javax.servlet.annotation.WebServlet;
 3 import javax.servlet.http.HttpServlet;
 4 import javax.servlet.http.HttpServletRequest;
 5 import javax.servlet.http.HttpServletResponse;
 6 import javax.servlet.http.HttpSession;
 7 import java.io.IOException;
 8
 9 @WebServlet(name = "LoginServlet",urlPatterns = "/login")
10 public class LoginServlet extends HttpServlet {
11     @Override
12     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
13        String username=request.getParameter("username");
14         HttpSession session=request.getSession();
15         session.setAttribute("username",username);
16         //重新定向到index.jsp
17         response.sendRedirect("index.jsp");
18     }
19
20     @Override
21     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
22
23     }
24 }

ExitServlet.java:

 1 package servlet;
 2
 3 import javax.servlet.ServletException;
 4 import javax.servlet.annotation.WebServlet;
 5 import javax.servlet.http.HttpServlet;
 6 import javax.servlet.http.HttpServletRequest;
 7 import javax.servlet.http.HttpServletResponse;
 8 import javax.servlet.http.HttpSession;
 9 import java.io.IOException;
10
11 @WebServlet(name = "ExitServlet",urlPatterns = "/exit")
12 public class ExitServlet extends HttpServlet {
13     @Override
14     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
15     //从session中移除loginName参数
16         response.getWriter().write("2222");
17         HttpSession session=request.getSession();
18         session.removeAttribute("username");
19         //重新定向到login.jsp
20         response.sendRedirect("login.jsp");
21     }
22
23     @Override
24     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
25     doPost(request, response);
26     }
27 }

OnlineListener.java:

 1 package listener;
 2
 3 import bean.User;
 4
 5 import javax.servlet.ServletContextEvent;
 6 import javax.servlet.ServletContextListener;
 7 import javax.servlet.http.HttpSessionAttributeListener;
 8 import javax.servlet.http.HttpSessionEvent;
 9 import javax.servlet.http.HttpSessionListener;
10 import javax.servlet.http.HttpSessionBindingEvent;
11
12 @javax.servlet.annotation.WebListener()
13 public class OnlineListener implements ServletContextListener,
14         HttpSessionListener, HttpSessionAttributeListener {
15     public OnlineListener() {
16     }
17     @Override
18     public void contextInitialized(ServletContextEvent sce) {
19
20     }
21     @Override
22     public void contextDestroyed(ServletContextEvent sce) {
23
24     }
25     @Override
26     public void sessionCreated(HttpSessionEvent se) {
27         System.out.println("会话已创建");
28     }
29     @Override
30     public void sessionDestroyed(HttpSessionEvent se) {
31         System.out.println("会话已销毁");
32     }
33
34     @Override
35     public void attributeAdded(HttpSessionBindingEvent sbe) {
36       //向session范围中添加一个用户
37         User.addUser(String.valueOf(sbe.getValue()));
38         System.out.println("session增加属性为"+sbe.getName()+"值为："+sbe.getValue());
39     }
40     @Override
41     public void attributeRemoved(HttpSessionBindingEvent sbe) {
42      //将session会话中的用户移除
43         User.removeUser(String.valueOf(sbe.getValue()));
44         System.out.println(sbe.getValue()+"属性已被移除");
45     }
46     @Override
47     public void attributeReplaced(HttpSessionBindingEvent sbe) {
48       //获取旧的属性值
49         String oldValue=String.valueOf(sbe.getValue());
50         //获取新的属性值
51         String newValue=String.valueOf(sbe.getSession().getAttribute(sbe.getName()));
52         //移除旧的属性，添加新的属性
53         User.removeUser(oldValue);
54         User.addUser(newValue);
55     }
56 }

用两个不同的浏览器运行结果如下图所示：

项目工程目录如下图：

（坚持学习！努力加油！勉励自己）

原文地址：https://www.cnblogs.com/crabmany/p/8605826.html