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

        class >com.oracle.com.MyListener class >

　　配置

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

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);
    }
}