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Hibernate plugin

Reload Hibernate EntityManagerFactory / SessionFactory after entity class definition/change. Clear Hibernate Validator reflection caches stored in BeanMetaDataManager and AnnotationMetaDataProvider classes.

The plugin hooks for initialization into org.hibernate.ejb.HibernatePersistence (for EJB 3.0) or org.hibernate.cfg.Configuration (for plain Hibernate) to wrap javax.persistence.EntityManagerFactory or org.hibernate.SessionFactory with a proxy. All clients then obtain reference for the proxy only.

Hibernte plugin listens for a change and hotswap on all classes on classpath. If the class contains @javax.persistence.Entity annotation, whole Hibernate configuration is reloaded and target factory is swapped in the proxy.

New EnityManager/SessionFactory instance is than obtained on next EnityManager.createEntityManager() call. EntityManager created before reload remains unchanged.

Implementation notes:

HibernateTransformers registers static transformer for main Hibernate configuration class org.hibernate.ejb.HibernatePersistence. The methods createEntityManagerFactory / createContainerEntityManagerFactory are wrapped with a call to HibernatePersistenceHelper.createContainerEntityManagerFactoryProxy, which creates a proxy and registers the proxy in static context to be accessible for the reloading.

Plugin instance HibernatePlugin.entityReload() / HibernatePlugin.newEntity() then listen for hotswap / new class file and schedules an HibernateRefreshCommands.reloadEntityManagerFactory() command to run in the application classloader. This translates directly to invocation of EntityManagerFactoryProxy.refreshProxiedFactories() which in turn calls refreshProxiedFactory() for each registered factory. The refresh is similar to standard Hibernate new configuration loading mechanism in org.hibernate.ejb.HibernatePersistence.

TODO:

  • Check for all Hibernate annotations (not just Entity)
  • Listen only on a package (not whole classpath) - probably hook somewhere in in the hibernate processing, because persistence.xml or .hbm.xml can be overridden by dynamic configuration (for example by Spring)
  • HibernatePlugin.entityReload - check if the class is an Entity can be resolved by Hibernate, not just the annotation.
  • Selective reload (because full reload is fast and very easy, this has low priority)