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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.
The 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. For example, the following Interceptor
automatically sets the createTimestamp
when an Auditable
is created and updates the lastUpdateTimestamp
property when an Auditable
is updated.
You can either implement Interceptor
directly or extend EmptyInterceptor
.
package org.hibernate.test; import java.io.Serializable; import java.util.Date; import java.util.Iterator; import org.hibernate.EmptyInterceptor; import org.hibernate.Transaction; import org.hibernate.type.Type; public class AuditInterceptor extends EmptyInterceptor { private int updates; private int creates; private int loads; public void onDelete(Object entity, Serializable id, Object[] state, String[] propertyNames, Type[] types) { // do nothing } public boolean onFlushDirty(Object entity, Serializable id, Object[] currentState, Object[] previousState, String[] propertyNames, Type[] types) { if ( entity instanceof Auditable ) { updates++; for ( int i=0; i < propertyNames.length; i++ ) { if ( "lastUpdateTimestamp".equals( propertyNames[i] ) ) { currentState[i] = new Date(); return true; } } } return false; } public boolean onLoad(Object entity, Serializable id, Object[] state, String[] propertyNames, Type[] types) { if ( entity instanceof Auditable ) { loads++; } return false; } public boolean onSave(Object entity, Serializable id, Object[] state, String[] propertyNames, Type[] types) { if ( entity instanceof Auditable ) { creates++; for ( int i=0; i<propertyNames.length; i++ ) { if ( "createTimestamp".equals( propertyNames[i] ) ) { state[i] = new Date(); return true; } } } return false; } public void afterTransactionCompletion(Transaction tx) { if ( tx.wasCommitted() ) { System.out.println("Creations: " + creates + ", Updates: " + updates, "Loads: " + loads); } updates=0; creates=0; loads=0; } }
There are two kinds of inteceptors: Session
-scoped and SessionFactory
-scoped.
A Session
-scoped interceptor is specified when a session is opened using one of the overloaded SessionFactory.openSession() methods accepting an Interceptor
.
Session session = sf.openSession( new AuditInterceptor() );
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 supplied 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.
new Configuration().setInterceptor( new AuditInterceptor() );
If you have to react to particular events in your persistence layer, you can also use the Hibernate3 event architecture. The event system can be used in addition, or as a replacement, for interceptors.
All the methods of the Session
interface correlate to an event. You have a LoadEvent
, a FlushEvent
, etc. Consult the XML configuration-file DTD or the org.hibernate.event
package for the full list of defined event types. When a request is made of one of these methods, the Hibernate Session
generates an appropriate event and passes it to the configured event listeners for that type. Out-of-the-box, these listeners implement the same processing in which those methods always resulted. However, you 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
.
The listeners should be considered singletons. This means they are shared between requests, and should not save any state as instance variables.
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). Custom listeners can either be registered programmatically through the Configuration
object, or specified in the Hibernate configuration XML. Declarative configuration through the properties file is not supported. Here is an example of a custom load event listener:
public class MyLoadListener implements LoadEventListener { // this is the single method defined by the LoadEventListener interface public void onLoad(LoadEvent event, LoadEventListener.LoadType loadType) throws HibernateException { if ( !MySecurity.isAuthorized( event.getEntityClassName(), event.getEntityId() ) ) { throw MySecurityException("Unauthorized access"); } } }
Vous avez aussi besoin d'une entrée de configuration disant à Hibernate d'utiliser ce listener en plus du listener par défaut :
<hibernate-configuration> <session-factory> ... <event type="load"> <listener class="com.eg.MyLoadListener"/> <listener class="org.hibernate.event.def.DefaultLoadEventListener"/> </event> </session-factory> </hibernate-configuration>
Instead, you can register it programmatically:
Configuration cfg = new Configuration(); LoadEventListener[] stack = { new MyLoadListener(), new DefaultLoadEventListener() }; cfg.EventListeners().setLoadEventListeners(stack);
Listeners registered declaratively cannot share instances. If the same class name is used in multiple <listener/>
elements, each reference will result in a separate instance of that class. If you need to share listener instances between listener types you must use the programmatic registration approach.
Why implement an interface and define the specific type during configuration? A listener implementation could implement multiple event listener interfaces. Having the type additionally defined during registration makes it easier to turn custom listeners on or off during configuration.
Usually, declarative security in Hibernate applications is managed in a session facade layer. Hibernate3 allows certain actions to be permissioned via JACC, and authorized via JAAS. This is an optional functionality that is built on top of the event architecture.
D'abord, vous devez configurer les listeners d'événements appropriés pour permettre l'utilisation d'autorisations JAAS.
<listener type="pre-delete" class="org.hibernate.secure.JACCPreDeleteEventListener"/> <listener type="pre-update" class="org.hibernate.secure.JACCPreUpdateEventListener"/> <listener type="pre-insert" class="org.hibernate.secure.JACCPreInsertEventListener"/> <listener type="pre-load" class="org.hibernate.secure.JACCPreLoadEventListener"/>
Note that <listener type="..." class="..."/>
is shorthand for <event type="..."><listener class="..."/></event>
when there is exactly one listener for a particular event type.
Next, while still in hibernate.cfg.xml
, bind the permissions to roles:
<grant role="admin" entity-name="User" actions="insert,update,read"/> <grant role="su" entity-name="User" actions="*"/>
Les noms de rôle sont les rôles compris par votre fournisseur JAAC.
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