JSR 303: How to Validate a Collection of annotated objects?

Question

Is it possible to validate a collection of objects in JSR 303 - Jave Bean Validation where the collection itself does not have any annotations but the elements contained within do?

For example, is it possible for this to result in a constraint violation due to a null name on the second person:

List<Person> people = new ArrayList<Person>();
people.add(new Person("dave"));
people.add(new Person(null));

Validator validator = Validation.buildDefaultValidatorFactory().getValidator();
Set<ConstraintViolation<List<Person>>> validation = validator.validate(people);

Answer 1

Yes, just add @Valid to the collection.

Here is an example from the Hibernate Validator Reference.

public class Car {
  @NotNull
  @Valid
  private List<Person> passengers = new ArrayList<Person>();
}

This is standard JSR-303 behavior. See Section 3.1.3 of the spec.

Answer 2

You, can also add @NotEmpty to the collection.

public class Car {
  @NotEmpty(message="At least one passenger is required")
  @Valid
  private List<Person> passengers = new ArrayList<Person>();
}

this will ensure at least one passenger is present, and the @Valid annotation ensures that each Person object is validated

Answer 3

You can of course also just iterate over the list and call Validator.validate on each element. Or put the List into some wrapper bean and annotate it with @Valid. Extending ArrayList for validation seems wrong to me. Do you have a particular use case you want to solve with this? If so maybe you can explain it a little more. To answer your initial question:

Is it possible to validate a collection of objects in JSR 303 - Jave Bean Validation where the collection itself does not have any annotations but the elements contained within do?

No

Answer 4

As of Bean Validator 2.0, both of these approaches work:

class MyDto {

    private List<@Valid MyBean> beans;
}

and

class MyDto {

    @Valid
    private List<MyBean> beans;
}

Answer 5

I wrote this generic class:

public class ValidListWrapper<T> {

    @Valid
    private List<T> list;

    public ValidListWrapper(List<T> list) {
        this.list = list;
    }

    public List<T> getList() {
        return list;
    }

}

If you are using Jackson library to deserialize JSON you can add @JsonCreator annotation on the constructor and Jackson will automatically deserialize JSON array to wrapper object.