How to avoid cross dependency between layers because of @Constraint validatedBy?

Question

In our project we have Service and DAO layers in separate Maven modules. Service module depends on DAO module and works with it\'s entities. The problem is that we can\'t pu

Answer 1

We faced the same issue in our Spring based project. To solve it in best Spring way we split ConstraintValidator interface and implementation. For example in domain layer we only have interface:

public interface UniqueValidator extends ConstraintValidator<Unique, String> {
}

In service layer we implement that interface:

public class UniqueValidatorJpaImpl implements UniqueValidator {
    private EntityManager entityManager;
    ...
}

Next we declare a bean in Spring Context for UniqueValidatorJpaImpl.

Finally to make all that staff working we extended SpringConstraintValidatorFactory. By default it only creates a new instance of class specified in validatedBy. We extended it by first looking in spring context for a bean of corresponding type:

public class SpringConstraintValidatorFactoryEx implements ConstraintValidatorFactory {

    private final Logger logger = LoggerFactory.getLogger(SpringConstraintValidatorFactoryEx.class);

    @Autowired
    private AutowireCapableBeanFactory beanFactory;

    public <T extends ConstraintValidator<?, ?>> T getInstance(Class<T> key) {
        T bean = null;

        try {
            logger.info("Trying to find a validator bean of class " + key.getSimpleName());
            bean = this.beanFactory.getBean(key);
        } catch (BeansException exc) {
            logger.info("Failed to find a bean of class " + key.getSimpleName());
        }

        if (bean == null) {
            try {
                logger.info("Creating a new validator bean of class " + key.getSimpleName());
                bean = this.beanFactory.createBean(key);
            } catch (BeansException exc) {
                logger.info("Failed to create a validator of class " + key.getSimpleName());
            }
        }

        if (bean == null) {
            logger.warn("Failed to get validator of class " + key.getSimpleName());
        }

        return bean;
    }

}

Answer 2

You may use an XML based constraint mapping to assign a validator to your constraint to avoid the reference from the annotation to the validator implementation.

The BV 1.1 EG is also discussing some improvements in that area. Feel free to weigh in on the issue on the mailing list.