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);      } }