Can you apply Bean Validation to arbitrary field types?

I can't find it explicitly stated in any of the documentation for JSR303/JSR380 bean validation (Jakarta Validation), but do all fields to which you apply validations have to be "essentially" plain-old-data (POD) types, like Strings and ints and Longs and such?

I tried to apply a regular expression validator to a UUID field, and I got a NoProviderFoundException thrown. I worked around it by just changing that field to a String and putting the onus of converting the field into a UUID on the consumer(s) of that class, but is there any way to create a custom "bean validation provider" mapped to an arbitrary non-POD class for cases where implementing a workaround isn't as straightforward?

Note: java.util.UUID is a serializable class, and therefore perfectly valid to include in a Bean.

Solution

Bean validation works for types, as long as the constraint annotation has a matching ConstraintValidator defined for it. I don't think that you can add support for extra types for the out-of-the-box annotations, but if you create your own custom annotation you can support all types you want.

A quick-and-dirty example based on @Pattern:

@Target({ElementType.FIELD, ElementType.METHOD}) // add others as needed
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = UuidValidator.class) // one for each type you want to support
@Documented
public @interface UuidPattern {

    String regexp();

    // mandated properties
    String message() default "UUID doesn't match pattern {regexp}";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};

    public class UuidValidator implements ConstraintValidator<UuidPattern, UUID> {

        private Pattern pattern;

        @Override
        public void initialize(UuidPattern annotation) {
            pattern = Pattern.compile(annotation.regexp());
        }

        @Override
        public boolean isValid(UUID uuid, ConstraintValidatorContext constraintValidatorContext) {
            if (uuid == null) {
                // let @NotNull handle this case
                return true;
            }
            return pattern.matcher().matches(uuid.toString());
        }
    }
}