Hibernate Validator is not tied to Hibernate for event based validation: a Java Persistence entity listener is available. Whenever an listened entity is persisted or updated, Hibernate Validator will verify all constraints of the entity instance and throw an exception if any constraint is violated. Basically, objects will be checked before any inserts and before any updates made by the Java Persistence provider. This includes changes applied by cascade! On constraint violation, the event will raise a runtime InvalidStateException which contains an array of InvalidValues describing each failure.

Here is how to make a class validatable:

@Entity
@EntityListeners( JPAValidateListener.class )
public class Submarine {
    ...
}