45_Listener_监听器_在线人数监听

来源：互联网发布：wps表格数据无法求和编辑：程序博客网时间：2024/06/13 06:20

使用注解 Listener@WebListener
在线人数
1. 人数放在何处？–公共区域（ServletContext）
2. 上线下线和什么有关？–HttpSession
OnlineListener

@WebListenerpublic class OnlineListener implements ServletContextListener,HttpSessionListener{    private ServletContext context=null;    private int count;    @Override    public void contextInitialized(ServletContextEvent sce) {        context=sce.getServletContext();        count=0;    }    @Override    public void contextDestroyed(ServletContextEvent sce) {     }    @Override    public void sessionCreated(HttpSessionEvent se) {        context.setAttribute("count", ++count);    }    @Override    public void sessionDestroyed(HttpSessionEvent se) {        context.setAttribute("count", --count);         }}

IndexServlet

public class IndexServlet extends HttpServlet {    @Override    protected void service(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        req.getSession().setAttribute("LL", "zhangsan");        resp.sendRedirect("index.jsp");    }}

index.jsp

<body>    在线人数：${applicationScope.count}</body>

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