jsp session/application

session的增加读取

 session.setAttribute("username", "张三");
 String u = (String) session.getAttribute("username");

application(服务器级别的，如果服务关了/或断电了，那么他就会消失)

 List onlineUserList = (List)  application.getAttribute("onlineUserList");
 if(onlineUserList == null)
 {
      onlineUserList = new ArrayList();
    application.setAttribute("onlineUserList", onlineUserList);
 }
 onlineUserList.add("张三");