13. Interceptors and events

It is useful for the application to react to certain events that occur inside Hibernate. This allows for the implementation of generic functionality and the extension of Hibernate functionality.

13.1. Interceptors

The org.hibernate.Interceptor interface provides callbacks from the session to the application, allowing the application to inspect and/or manipulate properties of a persistent object before it is saved, updated, deleted or loaded.

One possible use for this is to track auditing information. The following example shows an Interceptor implementation that automatically logs when an entity is updated.

public static class LoggingInterceptor extends EmptyInterceptor {
    @Override
    public boolean onFlushDirty(
        Object entity,
        Serializable id,
        Object[] currentState,
        Object[] previousState,
        String[] propertyNames,
        Type[] types) {
            LOGGER.debugv( "Entity {0}#{1} changed from {2} to {3}",
                entity.getClass().getSimpleName(),
                id,
                Arrays.toString( previousState ),
                Arrays.toString( currentState )
            );
            return super.onFlushDirty( entity, id, currentState,
                previousState, propertyNames, types
        );
    }
}

An Interceptor can be either Session-scoped or SessionFactory-scoped.

A Session-scoped interceptor is specified when a session is opened.

SessionFactory sessionFactory = entityManagerFactory.unwrap( SessionFactory.class );
Session session = sessionFactory
    .withOptions()
    .interceptor(new LoggingInterceptor() )
    .openSession();

Customer customer = session.get( Customer.class, customerId );
customer.setName( "Mr. John Doe" );
//Entity Customer#1 changed from [John Doe, 0] to [Mr. John Doe, 0]
session.flush();

A SessionFactory-scoped interceptor is registered with the Configuration object prior to building the SessionFactory. Unless a session is opened explicitly specifying the interceptor to use, the SessionFactory-scoped interceptor will be applied to all sessions opened from that SessionFactory. SessionFactory-scoped interceptors must be thread safe. Ensure that you do not store session-specific states, since multiple sessions will use this interceptor potentially concurrently.

SessionFactory sessionFactory = new MetadataSources( new StandardServiceRegistryBuilder().build() )
    .addAnnotatedClass( Customer.class )
    .getMetadataBuilder()
    .build()
    .getSessionFactoryBuilder()
    .applyInterceptor( new LoggingInterceptor() )
    .build();

13.2. Native Event system

If you have to react to particular events in the persistence layer, you can also use the Hibernate event architecture. The event system can be used in place of or in addition to interceptors.

Many methods of the Session interface correlate to an event type. The full range of defined event types is declared as enum values on org.hibernate.event.spi.EventType. When a request is made of one of these methods, the Session generates an appropriate event and passes it to the configured event listener(s) for that type.

Applications are free to implement a customization of one of the listener interfaces (i.e., the LoadEvent is processed by the registered implementation of the LoadEventListener interface), in which case their implementation would be responsible for processing any load() requests made of the Session.

A custom listener implements the appropriate interface for the event it wants to process and/or extend one of the convenience base classes (or even the default event listeners used by Hibernate out-of-the-box as these are declared non-final for this purpose). Here is an example of a custom load event listener:

Example 254. Custom LoadListener example

EntityManagerFactory entityManagerFactory = entityManagerFactory();
SessionFactoryImplementor sessionFactory = entityManagerFactory.unwrap( SessionFactoryImplementor.class );
sessionFactory
    .getServiceRegistry()
    .getService( EventListenerRegistry.class )
    .prependListeners( EventType.LOAD, new SecuredLoadEntityListener() );

Customer customer = entityManager.find( Customer.class, customerId );

13.3. Hibernate declarative security

Usually, declarative security in Hibernate applications is managed in a session facade layer. Hibernate allows certain actions to be authorized via JACC and JAAS. This is an optional functionality that is built on top of the event architecture.

First, you must configure the appropriate event listeners, to enable the use of JACC authorization. Again, see Event Listener Registration for the details.

Below is an example of an appropriate org.hibernate.integrator.spi.Integrator implementation for this purpose.

Example 255. JACC listener registration example

public static class JaccIntegrator implements ServiceContributingIntegrator {

    private static final Logger log = Logger.getLogger( JaccIntegrator.class );

    private static final DuplicationStrategy DUPLICATION_STRATEGY =
            new DuplicationStrategy() {
        @Override
        public boolean areMatch(Object listener, Object original) {
            return listener.getClass().equals( original.getClass() ) &&
                    JaccSecurityListener.class.isInstance( original );
        }

        @Override
        public Action getAction() {
            return Action.KEEP_ORIGINAL;
        }
    };

    @Override
    public void prepareServices(
            StandardServiceRegistryBuilder serviceRegistryBuilder) {
        boolean isSecurityEnabled = serviceRegistryBuilder
                .getSettings().containsKey( AvailableSettings.JACC_ENABLED );
        final JaccService jaccService = isSecurityEnabled ?
                new StandardJaccServiceImpl() : new DisabledJaccServiceImpl();
        serviceRegistryBuilder.addService( JaccService.class, jaccService );
    }

    @Override
    public void integrate(
            Metadata metadata,
            SessionFactoryImplementor sessionFactory,
            SessionFactoryServiceRegistry serviceRegistry) {
        doIntegration(
                serviceRegistry
                        .getService( ConfigurationService.class ).getSettings(),
                // pass no permissions here, because atm actually injecting the
                // permissions into the JaccService is handled on SessionFactoryImpl via
                // the org.hibernate.boot.cfgxml.spi.CfgXmlAccessService
                null,
                serviceRegistry
        );
    }

    private void doIntegration(
            Map properties,
            JaccPermissionDeclarations permissionDeclarations,
            SessionFactoryServiceRegistry serviceRegistry) {
        boolean isSecurityEnabled = properties
                .containsKey( AvailableSettings.JACC_ENABLED );
        if ( ! isSecurityEnabled ) {
            log.debug( "Skipping JACC integration as it was not enabled" );
            return;
        }

        final String contextId = (String) properties
                .get( AvailableSettings.JACC_CONTEXT_ID );
        if ( contextId == null ) {
            throw new IntegrationException( "JACC context id must be specified" );
        }

        final JaccService jaccService = serviceRegistry
                .getService( JaccService.class );
        if ( jaccService == null ) {
            throw new IntegrationException( "JaccService was not set up" );
        }

        if ( permissionDeclarations != null ) {
            for ( GrantedPermission declaration : permissionDeclarations
                    .getPermissionDeclarations() ) {
                jaccService.addPermission( declaration );
            }
        }

        final EventListenerRegistry eventListenerRegistry =
                serviceRegistry.getService( EventListenerRegistry.class );
        eventListenerRegistry.addDuplicationStrategy( DUPLICATION_STRATEGY );

        eventListenerRegistry.prependListeners(
                EventType.PRE_DELETE, new JaccPreDeleteEventListener() );
        eventListenerRegistry.prependListeners(
                EventType.PRE_INSERT, new JaccPreInsertEventListener() );
        eventListenerRegistry.prependListeners(
                EventType.PRE_UPDATE, new JaccPreUpdateEventListener() );
        eventListenerRegistry.prependListeners(
                EventType.PRE_LOAD, new JaccPreLoadEventListener() );
    }

    @Override
    public void disintegrate(SessionFactoryImplementor sessionFactory,
                             SessionFactoryServiceRegistry serviceRegistry) {
        // nothing to do
    }
}

You must also decide how to configure your JACC provider. Consult your JACC provider documentation.

13.4. JPA Callbacks

JPA also defines a more limited set of callbacks through annotations.

Table 6. Callback annotations

There are two available approaches defined for specifying callback handling:

• The first approach is to annotate methods on the entity itself to receive notification of particular entity life cycle event(s).

• The second is to use a separate entity listener class. An entity listener is a stateless class with a no-arg constructor. The callback annotations are placed on a method of this class instead of the entity class. The entity listener class is then associated with the entity using the javax.persistence.EntityListeners annotation

Example 256. Example of specifying JPA callbacks

@Entity
@EntityListeners( LastUpdateListener.class )
public static class Person {

    @Id
    private Long id;

    private String name;

    private Date dateOfBirth;

    @Transient
    private long age;

    private Date lastUpdate;

    public void setLastUpdate(Date lastUpdate) {
        this.lastUpdate = lastUpdate;
    }

    /**
     * Set the transient property at load time based on a calculation.
     * Note that a native Hibernate formula mapping is better for this purpose.
     */
    @PostLoad
    public void calculateAge() {
        age = ChronoUnit.YEARS.between( LocalDateTime.ofInstant(
                Instant.ofEpochMilli( dateOfBirth.getTime()), ZoneOffset.UTC),
            LocalDateTime.now()
        );
    }
}

public static class LastUpdateListener {

    @PreUpdate
    @PrePersist
    public void setLastUpdate( Person p ) {
        p.setLastUpdate( new Date() );
    }
}

These approaches can be mixed, meaning you can use both together.

Regardless of whether the callback method is defined on the entity or on an entity listener, it must have a void-return signature. The name of the method is irrelevant as it is the placement of the callback annotations that makes the method a callback. In the case of callback methods defined on the entity class, the method must additionally have a no-argument signature. For callback methods defined on an entity listener class, the method must have a single argument signature; the type of that argument can be either java.lang.Object (to facilitate attachment to multiple entities) or the specific entity type.

A callback method can throw a RuntimeException. If the callback method does throw a RuntimeException, then the current transaction, if any, must be rolled back.

A callback method must not invoke EntityManager or Query methods!

It is possible that multiple callback methods are defined for a particular lifecycle event. When that is the case, the defined order of execution is well defined by the JPA spec (specifically section 3.5.4):

• Any default listeners associated with the entity are invoked first, in the order they were specified in the XML. See the javax.persistence.ExcludeDefaultListeners annotation.

• Next, entity listener class callbacks associated with the entity hierarchy are invoked, in the order they are defined in the EntityListeners. If multiple classes in the entity hierarchy define entity listeners, the listeners defined for a superclass are invoked before the listeners defined for its subclasses. See the javax.persistence.ExcludeSuperclassListeners annotation.

• Lastly, callback methods defined on the entity hierarchy are invoked. If a callback type is annotated on both an entity and one or more of its superclasses without method overriding, both would be called, the most general superclass first. An entity class is also allowed to override a callback method defined in a superclass in which case the super callback would not get invoked; the overriding method would get invoked provided it is annotated.