Bean validation: at least one element of a list must have one field filled

Question

I have a list of lets say Car objects. Each car has a miles member. I need to validate (using Hibernate Validator) that at least one car in my list has a not null miles member. The best solution would be an annotation that would apply to all the elements of a collection, but would validate in the context of the whole collection.

I have two questions:

• Is there already an annotation for this (I do not know of any)?

• If there is no annotation for this, is there a way to create an generic annotation? I thought of specifiyng the name of the field that has to be not null at least for one element in the list, then I can apply this not only for Car classes.

  public class VechicleTransport {
  
      @AtLeastOneNotNull( fieldName = "miles" )
      private List<Car> carList;
  }
  
  
  public class Car {
  
    private Double miles;
  
      ....
  }
  

Answer 1

AFAIK there is no such annotation, You need to define custom constraint annotations and define your validation logic inside it.
Like
Defining custom constraint annotation AtLeastOneNotNull

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Constraint(validatedBy=AtLeastOneNotNullValidator.class)

public @interface AtLeastOneNotNull{
 String message() default "Your error message";
 Class<!--?-->[] groups() default {};
 Class<!--? extends Payload-->[] payload() default {};
}   

Defining validator for custom annotation.

public class AtLeastOneNotNullValidator implements ConstraintValidator<AtLeastOneNotNull, object=""> {

 @Override
 public void initialize(AtLeastOneNotNull constraint) {

 }

 @Override
 public boolean isValid(Object target, ConstraintValidatorContext context) {
    // Add logic to check if atleast one element have one field
 }
}

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