HttpSessionListener监听器实战

阳光穿透心脏的1/2处 2021-07-24 11:34 359阅读 0赞

**一 定义监听器**

package lee;
    
    import javax.servlet.*;
    import javax.servlet.annotation.*;
    import javax.servlet.http.*;import java.util.*;
    @WebListener
    public class OnlineListener
        implements HttpSessionListener
    {
        // 当用户与服务器之间开始session时触发该方法
        public void sessionCreated(HttpSessionEvent se)
        {
            HttpSession session = se.getSession();
            ServletContext application = session.getServletContext();
            // 获取session ID
            String sessionId = session.getId();
            // 如果是一次新的会话
            if (session.isNew())
            {
                String user = (String)session.getAttribute("user");
                // 未登录用户当游客处理
                user = (user == null) ? "游客" : user;
                Map<String , String> online = (Map<String , String>)
                    application.getAttribute("online");
                if (online == null)
                {
                    online = new Hashtable<String , String>();
                }
                // 将用户在线信息放入Map中
                online.put(sessionId , user);
                application.setAttribute("online" , online);
            }
        }
        // 当用户与服务器之间session断开时触发该方法
        public void sessionDestroyed(HttpSessionEvent se)
        {
            HttpSession session = se.getSession();
            ServletContext application = session.getServletContext();
            String sessionId = session.getId();
            Map<String , String> online = (Map<String , String>)
                application.getAttribute("online");
            if (online != null)
            {
                // 删除该用户的在线信息
                online.remove(sessionId);
            }
            application.setAttribute("online" , online);
        }
    }

**二 测试JSP**

<%@ page contentType="text/html; charset=GBK" language="java" errorPage="" %>
    <%@ page import="java.util.*" %>
    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
        "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
    <html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <title> 用户在线信息 </title>
        <meta name="website" content="http://www.crazyit.org" />
    </head>
    <body>
    在线用户：
    <table width="400" border="1">
    <%
    Map<String , String> online = (Map<String , String>)application
        .getAttribute("online");
    for (String sessionId : online.keySet())
    {%>
    <tr>
        <td><%=sessionId%>
        <td><%=online.get(sessionId)%>
    </tr>
    <%}%>
    </body>
    </html>

**三 测试结果**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70]: /images/20210724/d3b907190c1349988486f081f2bd1f6b.png