Instead of using @Digit
, I would like to suggest you to use @Pattern(message="YOUR_MESSAGE", regexp="REGULAR_EXPRESSION")
Main reason is that we show message for such set of values for which we want to restrict the user, here in your condition message is displayed for that value which you don't want to restrict.
So You wants to restrict user to enter anything other than blank space and numbers.Make a regular expression for that and use @Pattern with that.
For your case :
@Pattern(message="YOUR_MESSAGE", regexp="^(\\s*|\\d{10,15})$")