Spring 4.0 form validation issue using AJAX

I am facing problem when i am doing server side form validation using jQuery and spring 4. Every time "result" (object of BindingResult) is coming with zero error result.

Below I am proving my code for better understanding. my jsp code is

  <div class="registerForm">
                      <div class="modal-header">
                        <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>
                        <h4 class="modal-title" id="myModalLabel">Please Register</h4>
                      </div>
                      <div class="modal-body">
                            <form class="form-signin" id="regForm" commandName="userRegister">
                                <div class="reg-error error"></div><div class="reg-success success"></div>
                                <input type="text" name="username" class="input-block-level" placeholder="Username">
                                <input type="text" name="emailAddress" class="input-block-level" placeholder="Email address">
                                <input type="text" name="confirmEmailAdd" class="input-block-level" placeholder="Confirm Email address">
                                <input type="password" name="password" class="input-block-level" placeholder="Password">
                            </form>
                      </div>
                      <div class="modal-footer">
                        <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
                        <button type="button" class="btn btn-primary submitRegister">Register</button>
                      </div>
                  </div>

my script code is

 $.ajax({
                url: "${pageContext.request.contextPath}/register",    
                data: $('#regForm').serialize(), 
                type: "POST",
                success: function(result) {},
                error: function(XMLHttpRequest, textStatus, errorThrown){}
            });

My controller code is

@RequestMapping(value="/register", method = RequestMethod.POST)
    public @ResponseBody 
    ValidationResponse register(Model model, @ModelAttribute("userRegister") @Valid UserRegister userReg, BindingResult result) {
        ValidationResponse res = new ValidationResponse();

        if(result.hasErrors()){
            res.setStatus("FAIL");
            List<FieldError> allErrors = result.getFieldErrors();
            List<ErrorMessage> errorMesages = new ArrayList<ErrorMessage>();
            for (FieldError objectError : allErrors) {
                errorMesages.add(new ErrorMessage(objectError.getField(), objectError.getField() + "  " + objectError.getDefaultMessage()));
            }
            res.setErrorMessageList(errorMesages);

        } else {
            res.setStatus("SUCCESS");
        }
        return res;
    }

My bean object

public class UserRegister {

    @NotEmpty @NotNull
    private String username;

    @NotEmpty @NotNull
    private String password;

    @NotEmpty @Email @NotNull
    private String emailAddress;

setter and getters....
}

Do i need to do any other configuration or something else to get it validated properly?