Java annotation for Null but neither Empty nor Blank

Question

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 

Answer 1

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;     } } 

Answer 2

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).