Java annotation for Null but neither Empty nor Blank

Is there are any java annotation(s) that can validate like the example below?

String test;
test = null; //valid
test = ""; //invalid
test = " "; //invalid
test = "Some values"; //valid

You need to create a custom annotation: @NullOrNotBlank

First create the custom annotation: NullOrNotBlank.java

@Target( {ElementType.FIELD})
@Retention(RUNTIME)
@Documented
@Constraint(validatedBy = NullOrNotBlankValidator.class)
public @interface NullOrNotBlank {
    String message() default "{javax.validation.constraints.NullOrNotBlank.message}";
    Class<?>[] groups() default { };
    Class<? extends Payload>[] payload() default {};
}

Then the actual validator: NullOrNotBlankValidator.java

public class NullOrNotBlankValidator implements ConstraintValidator<NullOrNotBlank, String> {

    public void initialize(NullOrNotBlank parameters) {
        // Nothing to do here
    }

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

There isn't such an annotation in either javax.validation or Hibernate Validator. There was a request to add one to Hibernate Validator but it was closed as "won't fix" due to the possibility of writing your own relatively easily. The suggest solution was to either use your own annotation type defined like this:

@ConstraintComposition(OR)
@Null
@NotBlank
@ReportAsSingleViolation
@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER })
@Retention(RUNTIME)
@Constraint(validatedBy = { })
public @interface NullOrNotBlank {
    String message() default "{org.hibernate.validator.constraints.NullOrNotBlank.message}";
    Class<?>[] groups() default { };
    Class<? extends Payload>[] payload() default { };
}

or to use the @Pattern annotation with a regular expression that requires a non-whitespace character to be present (as the Pattern annotation accepts nulls and does not match them against the pattern).

Where is a nice javax.validation.constraints.Pattern annotation.

You can annotate the field with:

@Pattern(regexp = "^(?!\\s*$).+", message = "must not be blank")

This checks if field matches regex. The regex itself is something but not blank (see details here). It uses negative lookahead.