java - How can i get a session variable (setted with a servlet) in jstl -

i'm making application jsp , java servlets, problem
need check if session variable set (i set on servlet)
on jsp file. i'm using jstl cheking this, code is:

 string siguiente = "/vista2.jsp"; ... if(request.getparameter("user").equals(usdb) && request.getparameter("pass").equals(passdb)){                     out.println("coinciden usuario y contraseña
");                     httpsession hs = request.getsession(true);                     integer par = (integer)hs.getattribute("vars");                     if(par==null){                         random rg = new random();                         par = new integer(rg.nextint(1000));                         hs.setattribute("vars", par);                     }                     requestdispatcher dispatcher = getservletcontext().getrequestdispatcher(siguiente);                     dispatcher.forward(request, response);                     break;                 }

and in jsp code i'm trying

 <c:choose>
             <c:when test="${vars!=null}">
              <c:redirect url="/index.jsp" />
            </c:when>
            <c:otherwise>
              <h1>has entrado exitosamente</h1>   
           </c:otherwise>
       </c:choose> 

and though access page directly(without accessing servlet before) page doesn't redirect