Servlet的监听器实现在线人数统计

朱雀 2021-07-24 17:35 405阅读 0赞

**目录**

一 开发步骤

二 实战

三 测试

--------------------

# **一 开发步骤** #

1 编写监听器

2 注册监听器

# **二 实战** #

1 监听器编写

import javax.servlet.ServletContext;
    import javax.servlet.http.HttpSessionEvent;
    import javax.servlet.http.HttpSessionListener;
    
    
    /**
    * @ClassName: OnlineCount
    * @Description: 在线人数监听
    * @Date: 2020/6/15
    * @Author: cakin
    */
    public class OnlineCount implements HttpSessionListener {
        /**
         * 功能描述：会话创建时刻进行监听
         *
         * @param se 会话事件
         * @author cakin
         * @date 2020/6/15
         * @description: 创建一个会话时，在线人数加1
         */
        public void sessionCreated(HttpSessionEvent se) {
            ServletContext servletContext = se.getSession().getServletContext();
            Integer onlineCount = (Integer) servletContext.getAttribute("onlineCount");
            System.out.println("增加一个session");
            if (onlineCount == null) {
                onlineCount = 1;
            } else {
                int count = onlineCount.intValue();
                onlineCount = ++count;
            }
            servletContext.setAttribute("onlineCount", onlineCount);
        }
    
    
        /**
         * 功能描述：会话销毁时刻进行监听
         *
         * @param se 会话事件
         * @author cakin
         * @date 2020/6/15
         * @description: 销毁会话时，在线人数建1
         */
        public void sessionDestroyed(HttpSessionEvent se) {
            ServletContext servletContext = se.getSession().getServletContext();
            System.out.println("减少一个session");
            Integer onlineCount = (Integer) servletContext.getAttribute("onlineCount");
            if (onlineCount == null) {
                onlineCount = 0;
            } else {
                int count = onlineCount.intValue();
                onlineCount = --count;
            }
            servletContext.setAttribute("onlineCount", onlineCount);
        }
    }

2 注册监听器

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
             version="4.0">
        
        <listener>
            <listener-class>OnlineCount</listener-class>
        </listener>
        
        <session-config>
            <session-timeout>1</session-timeout>
        </session-config>
    </web-app>

3 JSP页面测试

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
    <html>
      <head>
        <title>$Title$</title>
      </head>
      <body>
      <h1>当前在线人数为<%=this.getServletConfig().getServletContext().getAttribute("onlineCount")%></h1>
      </body>
    </html>

# **三 测试** #

![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/20210724/6ef80934dd034c4d92664bd8f777b1d1.png