CustomGoogleEmailConstraint.java

@Documented 
@Constraint(validatedBy = CustomGoogleEmailValidator.class) 
@Target({ ElementType.METHOD, ElementType.FIELD }) 
@Retention(RetentionPolicy.RUNTIME) 
public @interface CustomGoogleEmailConstraint {
  String message() default "The email must have \"@gmail.com\" extension";
  Class[] groups() default {};
  Class[] payload() default {};
}