validation - 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;
    }
}