protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");

    HttpSession sesion = request.getSession();
    PrintWriter out = response.getWriter();

    String num = request.getParameter("num");
    String password = request.getParameter("password");
    sesion.setAttribute("num", num);

    Queries sql = new Queries();
    if (sql.login(num, password)) {
        response.sendRedirect("private.jsp");
    } else {
        request.setAttribute("error", "Error on login");
        RequestDispatcher dispatcher =
        ServletContext().getRequestDispatcher("login.jsp"); // This line doesn't working
        dispatcher.forward(request, response);
    }

}