Session使用（14）

用session统计某个网页的访问人数（因为我还不会js，所以就做了个简易版本的）

1、创建Session监听器，每创建了一个Session对象就执行监听类中·的sessionCreated方法。

package com.ykh.session;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public class SeesionLister 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);
    }
}

　　2、具体实现的servlet：

package com.ykh.session;import java.io.IOException;
import java.io.PrintWriter;import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;/**
 * Servlet implementation class SeesionTest
 */
@WebServlet("/Test")
public class SeesionTest extends HttpServlet {
private static final long serialVersionUID = 1L;    /**
     * @see HttpServlet#HttpServlet()
     */
    public SeesionTest() {
        super();
        // TODO Auto-generated constructor stub
    }/**
 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
 */
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// TODO Auto-generated method stub
req.setCharacterEncoding("utf-8");
       doPost(req,resp);
}/**
 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
 */
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// TODO Auto-generated method stub
//doGet(request, response);
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);
}}

　　3、效果：

链接：https://pan.baidu.com/s/1F4R-jdC2bhKO7iTmzaOyWA
提取码：whkm
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