Today I had to implement a change logging system for an application. The most changes to log came with UPDATE commands to the database. The idea: detect UPDATE commands by JPA and notify instead of place method-calls all over the code.
Fortunately Spring Boot and JPA provides some Entity-Lifecycle-Listeners:
@EntityListeners(AuditTrailListener.class)
@Entity
public class User {
//...
}
public class AuditTrailListener {
private static Log log = LogFactory.getLog(AuditTrailListener.class);
@PrePersist
@PreUpdate
@PreRemove
private void beforeAnyUpdate(User user) {
log.info("add/update/delete complete for user: " + user.getId());
}
@PostPersist
@PostUpdate
@PostRemove
private void afterAnyUpdate(User user) {
log.info("[USER AUDIT] add/update/delete complete for user: " + user.getId());
}
@PostLoad
private void afterLoad(User user) {
log.info("[USER AUDIT] user loaded from database: " + user.getId());
}
}
But for me it was not enough. My AuditTrailListener should be an Spring Boot class annotated with @Component. This together doesn't work. After some experiments I realized that JPA and Spring instantiate it's own objects of the Listener.
On stackoverflow.com I found another way to get my desired result:
@Component
public class MyEventListener implements PreInsertEventListener {
@Autowired
private EntityManagerFactory entityManagerFactory;
@PostConstruct
private void init() {
SessionFactoryImpl sessionFactory = entityManagerFactory.unwrap(SessionFactoryImpl.class);
EventListenerRegistry registry = sessionFactory.getServiceRegistry().getService(EventListenerRegistry.class);
registry.getEventListenerGroup(EventType.PRE_INSERT).appendListener(this);
}
@Override
public boolean onPreInsert(PreInsertEvent preInsertEvent) {
return false;
}
}
The EntityManagerFactory has an ServiceRegistry which can be extended with custom EventListeners. The example shows the PreInsertEvent, but there are all Pre and Post Insert/Update/Delete events ready for you.
