[hibernate-dev] Concept of "service availability"

This ties together a few different discussions that have been going on simultaneously on the mailing list that I think are all related. Right now to configure certain services (select one impl over another) users generally give the FQN for that impl Class. For example to use C3P0 connection pooling users would say: hibernate.connection.provider_class = org.hibernate.service.jdbc.connections.internal.C3P0ConnectionProvider We have discussed why this is bad even before any of the OSGi discussions and the solution we wanted to shoot for was that of naming "selectors" such that the user would instead say: hibernate.connection.provider_class = c3p0 And "c3p0" here would be interpreted to mean "instantiate and configure the org.hibernate.service.jdbc.connections.internal.C3P0ConnectionProvider Class". But that still means a limited set of short name values *and* still gives us a problem (iiuc) under OSGi due to visibility. So what I propose instead is a way for service implementors to be registered under a short name via discovery. The main piece to this is the "registry" (which is also a service under the BootstrapServiceRegistry): interface AvailableServiceRegistry extends Service { public <T> Class<? extends T> findAvailableServiceImplementor(Class<T> serviceRole, String selector); } class AvailableServiceRegistryImpl implements AvailableServiceRegistry, ServiceRegistryAwareService { private Map<Class,Map<String,Class>> availableImplementors = ...; @Override public <T> Class<? extends T> findAvailableServiceImplementor(Class<T> serviceRole, String selector) { // purposely simplistic :) return availableImplementors.get( serviceRole ).get( selector ); } @Override public void injectServices(ServiceRegistryImplementor serviceRegistry) { final LinkedHashSet<ServiceAvailabililtyNotifier> notifiers = serviceRegistry.getService( ClassLoaderService.class ).loadJavaServices( ServiceAvailabililtyNotifier.class ); for ( ServiceAvailabililtyNotifier notifier : notifiers ) { for ( ServiceAvailabililty availability : notifier.getAvailabilities() ) { // again, purposely simplistic Map<String,Class> serviceImplementors = availableImplementors.get( availability.getRole() ); serviceImplementors.put( availability.getSelector(), availability.getImplementor() ); } } } } Outstanding question... Especially in OSGi, where service bundles can be added/removed, how do we best account for cleaning up no-longer valid references (even more importantly perhaps, what the hell does it mean to Hibernate when a ConnectionProvider implementation, for example, that is in use gets taken away?!?). Perhaps this is just where an OSGi-specific Hibernate ServiceRegistry implementation would come into play. -- steve(a)hibernate.org http://hibernate.org