Validation services for complex domain objects.

Generally you will write Validators for each of your domain objects, and add a {@link ValidationManager} to your application context. You will need to wire a suitable {@link IntrospectionManager} against the ValidationManager so that children of a domain object presented for validation can be identified and in turn also validated.

The {@link ValidationInterceptor} and {@link ValidationAdvisor} should be used against each of your data access object (DAO) mutator methods, such as SomeDao.create(Object) and SomeDao.update(Object). The interceptor will cause the Object to be presented to the ValidationManager, thus ensuring the domain object instance is in a valid state before being persisted.

If you domain objects themselves wish to ensure they are in a valid state prior to internal business methods being invoked, it is suggested they provide a ValidationManager collaborator, and fire its validate method. Such collaborator can be autowired during both instance retrieval and creation. It should generally also be marked as transient, to avoid possible serialisation issues if used inside a HttpSession or similar.

Sometimes domain objects need to internally update themselves before being validated. Any such domain objects should implement {@link BindBeforeValidation}. The ValidationManager will fire the related method just prior to validation, and you can do it manually using {@link BindBeforeValidationUtils}. Using the utility class is generally preferred over calling the method directly, as it ignores classes that do not implement BindBeforeValidation.

Finally, sometimes Validators might need to perform queries against a persistence or services layer. For example, the Validator may be checking no other user has this username. If using an ORM tool such as Hibernate, it is recommended your Validators subclass a common abstract parent that provides an evict(Object) and evict(Collection) method. That way your Validators can utilise standard services layer or DAO methods as required to retrieve other domain objects, and flush them from the session cache afterwards. Whilst this is more a Validator design choice than something mandated by this package, we have found it a worthwhile pattern in real-world applications.