validation annotations with OR?

bbeloff · **Joined:** Fri Jul 08, 2011 8:45 am **Posts:** 6

Hi

I've got a pretty simple validation requirement for a field. I've read the Hibernate Validator reference, but I still can't figure out how to do this.

I want to specify that a field should EITHER be empty, OR contain at least nine characters.

How do I do this?

Thanks for your help.

Bruno.

Gunnar · **Joined:** Sat Jan 24, 2009 12:46 pm **Posts:** 388

Hi,

do you mean by empty an empty string ("") or actually null? In case of the latter you could simply use the @Size annotation, as all built-in constraints allow null as valid value. Assuming you're validating values from an UI there might be an option supported by your UI framework which automatically converts empty strings to null. In JSF 2 for example there is the option javax.faces.INTERPRET_EMPTY_STRING_SUBMITTED_VALUES_AS_NULL.

In case you really have to deal with empty strings you might use the @Pattern constraint with a regular expression which accepts the empty string or requires at least 9 characters such as this:

Code:

@Pattern(regexp = "^|.{9,}")
String myString;

Hope that helps,

--Gunnar

Gunnar · **Joined:** Sat Jan 24, 2009 12:46 pm **Posts:** 388

Just thought a bit more about this :)

If you're using HV 4.2 you could also create a reusable constraint @EmptyOrSize based on the boolean constraint composition feature introduced with 4.2. This could roughly look like this:

Code:

@ConstraintComposition(CompositionType.OR)
@Pattern(regexp = "")
@Size
@ReportAsSingleViolation
@Target({ ElementType.METHOD, ElementType.FIELD })
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = { })
public @interface EmptyOrSize {

   String message() default "{EmptyOrSize.message}";
   Class<?>[] groups() default { };
   Class<? extends Payload>[] payload() default { };
   
   @OverridesAttribute(constraint = Size.class, name = "min")
   int min() default 0;
   
   @OverridesAttribute(constraint = Size.class, name = "max")
   int max() default Integer.MAX_VALUE;

}

This constraint could be used like this:

Code:

@EmptyOrSize(min=9)
String myString;

--Gunnar

bbeloff · **Joined:** Fri Jul 08, 2011 8:45 am **Posts:** 6

Hi Gunnar

Brilliant!

In fact, I use a binder with StringTrimmerEditor. I trim, but I don't convert to null, because I want to be able to distinguish between fields that have been set to empty, and those that have never been set.

And I was being stupid - of course, @Pattern is always going to be flexible enough to cope with these situations! I just have to get my regexp head on.

The custom constraint is the most elegant, especially because I can see this type of constraint being used in multiple places in the application. I'm currently using HV 4.1. I'll see if I can shift to 4.2 without breaking anything.

Thank you very much for this.

--Bruno.