@RequestMapping(value = "/login", method = RequestMethod.POST,produces = "application/json")
public @ResponseBody Map<String, String> validateUser(@RequestBody String loginParameters,HttpServletRequest request) throws Exception {
    try{
        HttpSession session=request.getSession();
        JSONObject json = new JSONObject(loginParameters.trim());
        String un=json.getString("username");
        session.setAttribute("username", un);