And / Or condition in Spring annotation based validation

Question

I am using Spring 3 annotation based validation. I want to add a following validation for String fields

Field can be Null OR it should contain a non empty string

I know annotation like @Null, @NotEmpty but how I can use both with a OR condition?

---

Solution:

Using @Size(min=1) helps but it don't handle spaces. So added a custom annotation NotBlankOrNull which will allow null and non empty strings also it takes care of blank spaces. Thanks a lot @Ralph.
Here is my Annotation

@Documented
@Constraint(validatedBy = { NotBlankOrNullValidator.class })
@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER })
@Retention(RUNTIME)
public @interface NotBlankOrNull {
    String message() default "{org.hibernate.validator.constraints.NotBlankOrNull.message}";

    Class<?>[] groups() default { };

    Class<? extends Payload>[] payload() default { };
}

Validator class

public class NotBlankOrNullValidator implements ConstraintValidator<NotBlankOrNull, String> {

    public boolean isValid(String s, ConstraintValidatorContext constraintValidatorContext) {
        if ( s == null ) {
            return true;
        }
        return s.trim().length() > 0;
    }

    @Override
    public void initialize(NotBlankOrNull constraint) {

    }
} 

I have also updated it on my site.

Answer 1

First of all, it is not Spring annotation based validation, it is JSR 303 Bean Validation, implemented for example by Hibernate Validation. It is really not spring related/

You can not combine the annotations in an OR way*.

But there is a simple workaround for the not null constraint, because the most basic validations accept null as an valid input (therefore you often need to combine the basic vaidations and an extra @NotNull, if you want to have a "normal" behavior but not what you asked for).

For Example: @javax.validation.constraints.Size accept null as an valid input.

So what you need in your case is use @Size(min=1) instead of @NotEmpty.

BTW: Not @NotEmpty is just an combination of @NotNull and @Size(min = 1)

*except you implement it by your self.