private void verifyUser(User user) throws UserServiceException {
   if (this.userExists(user.getUsername())) {
     throw new UsernameAlreadyExistsException(
         "Username " + user.getUsername() + " already exists");
   }
   if (this.emailExists(user.getEmail())) {
     throw new EmailAlreadyInUseException("Email " + user.getEmail() + " already exists");
   }
 }