问HttpServletRequest#login()在Java中不起作用

EN

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        try {
            String strUsername = request.getParameter("txtusername");
            String strPassword = request.getParameter("txtpassword");
            if(strUsername == null || strPassword == null || strUsername.equals("") || strPassword.equals(""))
                throw new Exception("Username and/or password missing.");
            request.login(strUsername, strPassword);
            System.out.println("Login succeeded!!");

            if(request.isUserInRole(ROLES.ADMIN.getValue())){//enum
                System.out.println("Found in Admin Role");
                response.sendRedirect("/app/Admin/home.jsf");

            }
            else if (request.isUserInRole(ROLES.GENERAL.getValue()))
                response.sendRedirect("/app/Common/index.jsf");
            else //guard
                throw new Exception("No role for user " + request.getRemoteUser());


        }catch(Exception ex){
            //patch work why there needs to be blogger here?
            System.out.println("Invalid username and/or password!!");
            response.sendRedirect("/app/Common/index.jsf");
        }finally {
            out.close();
        }
    }