监听器----如何使用监听器记录注册用户的在线状态?
Posted 波光闪烁
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首先写一个登陆界面----index.jsp
<body> <form action="${pageContext.request.contextPath }/loginServlet" method="post"> 用户名：<input name="uname"/><br/> 密码：<input name="pwd" type="password"/><br/> <input type="submit" value="登录"/> </form> </body>
点击登陆,跳转至----loginServlet
@WebServlet(name="loginServlet",urlPatterns="/loginServlet") //Serclet3.0注解配置 public class LoginServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String name = request.getParameter("uname"); //获取用户名 String pwd = request.getParameter("pwd"); //获取密码 if("jack".equals(name) && "bdqn".equals(pwd)){ //判断用户名与密码是否正确 request.getSession().setAttribute("name", name); //将name放到session作用域里 request.getRequestDispatcher("online.jsp").forward(request, response); //跳转至登录成功界面 }else if ("tom".equals(name) && "123".equals(pwd)) { //第二个用户 request.getSession().setAttribute("name", name); request.getRequestDispatcher("online.jsp").forward(request, response); }else { request.getRequestDispatcher("401.jsp").forward(request, response); //如果未成功登录,跳转至401界面,可返回重新登录 } } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }
未成功登陆----401.jsp
<body> 请先登录，点击返回<a href="${pageContext.request.contextPath }/index.jsp">登录</a>页面 </body>
成功登录---online.jsp
<body> 登录成功！当前在线人数：${applicationScope.num } <!-- 监听器获取在线人数 --> <a href="${pageContext.request.contextPath }/logoutServlet">退出</a> </body>
退出处理----LogoutServlet
@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); } }
设置监听器----首先需要在web.xml里配置
<listener> <listener-class>cn.bdqn.listener.DemoListemer</listener-class> </listener>
监听器类 DemoListemer 继承 HttpSessionAttributeListener 接口
public class DemoListemer implements HttpSessionAttributeListener{ @Override public void attributeAdded(HttpSessionBindingEvent event) { int num=0; //定义初始在线人数为0 ServletContext servletContext = event.getSession().getServletContext();//使用session来判断是否为注册用户 Object object = servletContext.getAttribute("num"); //获取人数num if(object==null){ num=1; //object为null,说明是第一个登录的用户 }else { num=(Integer)object+1; //如果不为null,就在原人数上+1; } servletContext.setAttribute("num", num); } @Override public void attributeRemoved(HttpSessionBindingEvent event) { ServletContext servletContext = event.getSession().getServletContext(); Object object = servletContext.getAttribute("num"); //获取人数num int num=(Integer)object-1; //退出登录后人数-1 servletContext.setAttribute("num", num); //变更人数后设置给num } @Override public void attributeReplaced(HttpSessionBindingEvent event) { // TODO Auto-generated method stub } }
登录成功页面图
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