More Advanced Features - Beginning Hibernate: From Novice to Professional - page 256

Financial packages often require considerable auditing information to be maintained to
prevent fraud and aid accountability. Auditing is a natural candidate for implementation as an
interceptor, as it would normally require that no changes be made to the persistence process
at all.
The question that usually arises when discussing interceptors is “why not use triggers?”
Triggers should never embody application logic, only business logic. If any application is
going to have audit-free access to the database, you cannot implement the auditing in trig-
gers. Worse, the triggers may not have access to the user information that's needed. In most
multi-tier situations, the need to pool the database connections precludes establishing indi-
vidual user logins to the database. So, for example, the trigger would only know that a user
with the login “MonolithicApplication” carried out an update of last year's sales figures—not
that it was carried out by, say, Jim from accounts, which is who the auditors are likely to be
interested in! Table A-2 summarizes the points in the application life cycle at which the vari-
ous methods will be invoked.

Table A-2. The Interceptor Methods

Name When Invoked Comments

afterTransactionBegin()

Invoked immediately after a call to This method can change the state

begin() on a Transaction object

of the transaction—for example, it

retrieved from the Session object. can call rollback() .

afterTransactionCompletion()

Invoked immediately after the
completion of a transaction.

beforeTransactionCompletion()

Invoked immediately prior to the
completion of a transaction. This
method can change the state of the
transaction—for example, it can
call rollback() .

findDirty() Invoked during calls to flush() .

This allows the saving of changes
to attributes to be prevented or
forced.

getEntity()

Invoked when an entity not in the
Session object's own cache is
requested by its identifier.

getEntityName() Invoked when the Session object

needs to determine the name of a
given entity.

instantiate()

Invoked when the Session object Because the “empty” object can be

needs to create an entity instance. created here, this allows Hibernate

(in legacy applications, for exam-
ple) to use entities that do not
have a default constructor.

isTransient() Invoked when the Session object

needs to determine whether an
entity it has been asked to persist
is transient—for example, during
calls to saveOrUpdate() .

onDelete()

Invoked before an object is deleted. The object's state should not be

tampered with at this point.