In your servlet, you must use the passed in request object to obtain 'the' session, not just any session. This might be the problem if you're not doing it.
Session ses = request.getSession();
ses.setAttribute("hello", "hello");
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Then you get the RequestDispatcher and forward
RequestDispatcher rd = getRequestDispatcher("/somePage.jsp");
rd.forward(request, response);
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inside somePage.jsp,
you should be able to access "hello" like you already know how to do.