Reload Hibernate (4+5) EntityManagerFactory / SessionFactory after entity class definition/change.

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)