監聽器----如何使用監聽器記錄註冊用戶的在線狀態?

時間 2019-11-15

標籤監聽器如何使用記錄註冊用戶在線狀態简体版

原文原文鏈接

首先寫一個登錄界面----index.jspweb

<body>
    <form action="${pageContext.request.contextPath }/loginServlet" method="post">
        用戶名：<input name="uname"/><br/>
        密碼：<input name="pwd" type="password"/><br/>
        <input type="submit" value="登陸"/>
    </form>
  </body>

點擊登錄,跳轉至----loginServletsession

@WebServlet(name="loginServlet",urlPatterns="/loginServlet") //Serclet3.0註解配置
public class LoginServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String name = request.getParameter("uname"); //獲取用戶名
        String pwd = request.getParameter("pwd");   //獲取密碼
        if("jack".equals(name) && "bdqn".equals(pwd)){  //判斷用戶名與密碼是否正確
            request.getSession().setAttribute("name", name);   //將name放到session做用域裏
            request.getRequestDispatcher("online.jsp").forward(request, response); //跳轉至登陸成功界面
        }else if ("tom".equals(name) && "123".equals(pwd)) { //第二個用戶
            request.getSession().setAttribute("name", name);
            request.getRequestDispatcher("online.jsp").forward(request, response);
        }else {
            request.getRequestDispatcher("401.jsp").forward(request, response); //若是未成功登陸,跳轉至401界面,可返回從新登陸
        }
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
}

未成功登錄----401.jspapp

<body>
    請先登陸，點擊返回<a href="${pageContext.request.contextPath }/index.jsp">登陸</a>頁面
</body>

成功登陸---online.jspjsp

<body>
    登陸成功！當前在線人數：${applicationScope.num } <!-- 監聽器獲取在線人數 -->
    <a href="${pageContext.request.contextPath }/logoutServlet">退出</a>
</body>

退出處理----LogoutServletide

@WebServlet(name="logoutServlet",urlPatterns="/logoutServlet") 
public class LogoutServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        request.getSession().removeAttribute("name");
        request.getRequestDispatcher("index.jsp").forward(request, response);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
}

設置監聽器----首先須要在web.xml裏配置post

<listener>
      <listener-class>cn.bdqn.listener.DemoListemer</listener-class>
  </listener>

監聽器類 DemoListemer 繼承 HttpSessionAttributeListener 接口url

public class DemoListemer implements HttpSessionAttributeListener{

    @Override
    public void attributeAdded(HttpSessionBindingEvent event) {
        int num=0;  //定義初始在線人數爲0
        ServletContext servletContext = event.getSession().getServletContext();//使用session來判斷是否爲註冊用戶
        Object object = servletContext.getAttribute("num");  //獲取人數num
        if(object==null){
            num=1;  //object爲null,說明是第一個登陸的用戶
        }else {
            num=(Integer)object+1;  //若是不爲null,就在原人數上+1;
        }
        servletContext.setAttribute("num", num);
    }

    @Override
    public void attributeRemoved(HttpSessionBindingEvent event) {
        ServletContext servletContext = event.getSession().getServletContext();
        Object object = servletContext.getAttribute("num"); //獲取人數num
        int num=(Integer)object-1;  //退出登陸後人數-1
        servletContext.setAttribute("num", num);  //變動人數後設置給num
    }

    @Override
    public void attributeReplaced(HttpSessionBindingEvent event) {
        // TODO Auto-generated method stub
        
    }
}

登陸成功頁面圖spa

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