java web用監聽器listener簡單的實現線上統計人數

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   今天又重新學習了java web的基礎 監聽器技術，用sessionListener簡單的實現了網頁統計線上人數 （有一個bug就是當關閉網頁的時候 session不會關閉依舊存在，除非關閉伺服器），代碼如下(前端網頁代碼就不顯示了):

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     @Override12     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.jsp17         response.sendRedirect("index.jsp");18     }19 20     @Override21     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     @Override14     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {15     //從session中移除loginName參數16         response.getWriter().write("2222");17         HttpSession session=request.getSession();18         session.removeAttribute("username");19         //重新定向到login.jsp20         response.sendRedirect("login.jsp");21     }22 23     @Override24     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     @Override18     public void contextInitialized(ServletContextEvent sce) {19      20     }21     @Override22     public void contextDestroyed(ServletContextEvent sce) {23     24     }25     @Override26     public void sessionCreated(HttpSessionEvent se) {27         System.out.println("會話已建立");28     }29     @Override30     public void sessionDestroyed(HttpSessionEvent se) {31         System.out.println("會話已銷毀");32     }33     34     @Override35     public void attributeAdded(HttpSessionBindingEvent sbe) {36       //向session範圍中添加一個使用者37         User.addUser(String.valueOf(sbe.getValue()));38         System.out.println("session增加屬性為"+sbe.getName()+"值為："+sbe.getValue());39     }40     @Override41     public void attributeRemoved(HttpSessionBindingEvent sbe) {42      //將session會話中的使用者移除43         User.removeUser(String.valueOf(sbe.getValue()));44         System.out.println(sbe.getValue()+"屬性已被移除");45     }46     @Override47     public void attributeReplaced(HttpSessionBindingEvent sbe) {48       //擷取舊的屬性值49         String oldValue=String.valueOf(sbe.getValue());50         //擷取新的屬性值51         String newValue=String.valueOf(sbe.getSession().getAttribute(sbe.getName()));52         //移除舊的屬性，添加新的屬性53         User.removeUser(oldValue);54         User.addUser(newValue);55     }56 }

用兩個不同的瀏覽器運行結果如所示：

項目工程目錄如：

（堅持學習！努力加油！勉勵自己）

java web用監聽器listener簡單的實現線上統計人數