Where do add additional logic for validation that makes db calls?

My create controller method looks like this:

Code:

---

@RequestMapping(value = "/create", method = RequestMethod.POST)
    public ModelAndView create(@Valid AccountForm accountForm, BindingResult bindingResult) {

        ModelAndView mav = new ModelAndView("accounts/new");
        mav.addObject("errors", bindingResult.getAllErrors());
        mav.addObject("accountForm", accountForm);

        if (bindingResult.hasErrors()) {
            return mav;
        }
      // more code here
    }

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Now my accountForm class has simple validations on the fields like NotNull, Size, Pattern, etc. For example:

Code:

---

  @NotNull(message = "Email cannot be empty.")
    @Size(min=3, max=20, message="Email must be between 3 and 100 characters long.")
    private String email;

---

What if I need to make a database call? e.g. to make sure the email address is not a duplicate, etc.

I'm planning on doing this for now:

Code:

---

if(!bindingResult.hasErrors()) {
  if(userService.doesEmailExist(accountForm.getEmail())) {
      bindingResult.addError(new ObjectError("email", "Email address already exists.")); 
  }
}

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But I don't like this approach since the validation logic in not encapsulated in a single place.
Is there a better way?