通过session统计当前在线人数

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通过session统计当前在线人数

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<!-- 监听器配置 -->
    <listener>
        <listener-class>com.oracle.com.MyListener</listener-class>
    </listener>

　　配置

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package com.oracle.com;
 
import javax.servlet.ServletContext;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
 
public class MyListener implements HttpSessionListener {
 
    @Override
    public void sessionCreated(HttpSessionEvent event) {
        // System.out.println("创建了");
        HttpSession session = event.getSession();// 获得Session对象
        // 通过Session获得servletcontext对象
        ServletContext servletContext = session.getServletContext();
        /**
         * 1.获取num值
         * 2.加1
         * 3.存入servletcontext
         */
        Object object = servletContext.getAttribute("num");
        if (object == null) {
            servletContext.setAttribute("num", 1);
        } else {
            Object num = servletContext.getAttribute("num");
            int num1 = (int) num;
            servletContext.setAttribute("num", num1 + 1);
        }
    }
 
    @Override
    public void sessionDestroyed(HttpSessionEvent event) {
        // System.out.println("销毁了");
        HttpSession session = event.getSession();// 获得Session对象
        // 通过Session获得servletcontext对象
        ServletContext servletContext = session.getServletContext();
        /**
         *  1.获取num值
         *  2.减1
         *  3.存入servletcontext
         */
        servletContext.setAttribute("num", (long) servletContext.getAttribute("num") - 1);
    }
 
}

　　统计

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package com.oracle.com;
 
import java.io.IOException;
import java.io.PrintWriter;
 
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
 
public class servletDemo5 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }
 
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        HttpSession session = req.getSession();// 创建Session
        // session.setMaxInactiveInterval(10);//设置失效时间10秒 不是销毁
        PrintWriter writer = resp.getWriter();
        ServletContext servletContext = getServletContext();
        Object num = servletContext.getAttribute("num");
        writer.write("在线人数:" + num);
    }
}

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