Preserving session in Java with sendredirect

I am creating a Login Application in JAVA.I am making the presentation in JSP and all the logic (Database connectivity) in Servlet [this is not a right approach I know that]. I check the username Password in Servlet and then create a session variable. and add the session like this

sess.setAttribute("username",oName);

Then I redirect the user to its homepage say student.jsp

response.sendRedirect("student.jsp");

It removes the session variable.I need a way to preserve the session variable and move to student.jsp.I tried to use forwading but that didn't worked out.

RequestDispatcher dispatcher =
                getServletContext()
                    .getRequestDispatcher("/student.jsp");

            if (dispatcher != null) {
                dispatcher.forward(request, response);
            }

It forward request but the Page address doesn't change to student.jsp which is not good. Any help in this regard will be appreciated Thank you