Java – spring validates a string list of non empty elements

I have a model class that contains a list of strings The list can be empty or contain elements If it has elements, they cannot be empty For example, suppose I have a class named questionpaper, which has a list of questionids, each of which is a string

class QuestionPaper{
private List<String> questionIds;
....
}

The paper can have zero or more questions However, if there is a problem, the ID value cannot be an empty string I am writing a microservice using springboot, hibernate, JPA and Java How should I do this verification Any help is appreciated

For example, we need to reject the following JSON input from the user

{ "examId": 1,"questionIds": [ ""," ","10103" ] }

Is there any out of the box way to achieve this, or do I have to write a custom validator for it

Solution

Custom validation comments should not be a problem:

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = NotEmptyFieldsValidator.class)
public @interface NotEmptyFields {

    String message() default "List cannot contain empty fields";

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

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

}


public class NotEmptyFieldsValidator implements ConstraintValidator<NotEmptyFields,List<String>> {

    @Override
    public void initialize(NotEmptyFields notEmptyFields) {
    }

    @Override
    public boolean isValid(List<String> objects,ConstraintValidatorContext context) {
        return objects.stream().allMatch(nef -> nef != null && !nef.trim().isEmpty());
    }

}

Usage? Simple:

class QuestionPaper{

    @NotEmptyFields
    private List<String> questionIds;
    // getters and setters
}

PS: no test logic, but I think it's good