java - Sessions in Spring MVC -

i know how sessions gets used in spring mvc retain value until user logged in.

somewhere found model.addattribute("session_name",username); creating session & access ${username} in jsp page. real way web can define & access username variable in pages?

how can check if session variable name username exists? in jsp used use

if(null == session.getattribute("username")){     // user not logged in.   }else{     // user logged in.   }  

how can check in spring mvc ?

session created spring container when need put in arguments of controllers method , injected. user login example

@requestmapping(value=("login"),method=requestmethod.post) public string login(@requestparam("name")string name,@requestparam("pass")string pass,@requestparam("gname")string gname,httpsession session         ) {      user u1=new user();     u1.setname(name);     u1.setgname(gname);     u1.setpass(pass);     user u2=dao.findbyid(name);     if(u2!=null)     { if(u1.getpass().equals(u2.getpass())&&u1.getgname().equals(u2.getgname()))         {              session.setattribute("user", u1);             return "welcome";         }         else         {             return "error";         }     }     else     {         return "error";     }   } 

now can in jsp page following way:

if(session.getattribute("user")!=null) {     user user=(user)session.getattribute("user");  } else  {    out.print("log in please");   }