Session factory for Hibernate 4 using buildSessionFactory and ServiceRegistry

In Hibernate 3:

private static SessionFactory factory;

Configuration config = HibernateUtil.getInitializedConfiguration();
factory = config.buildSessionFactory();
Session session = factory.getCurrentSession();

In Hibernate 4:
You need to pass a ServiceRegistry class to buildSessionFactory:

Configuration config = new Configuration().configure("hibernate.cfg.xml");
config.addAnnotatedClass(DatastreamTriggers.class); //your JPA models
config.addAnnotatedClass(Follower.class);//your JPA models
config.addAnnotatedClass(Subject.class);//your JPA models
serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();
factory = config.buildSessionFactory(serviceRegistry);
Session session = factory.getCurrentSession();

Using metadatasources:

ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().configure().buildServiceRegistry();
MetadataSources metadataSources = new MetadataSources(serviceRegistry);
metadataSources.addResource("some_mapping.hbm.xml")
SessionFactory sessionFactory = metadataSources.buildMetadata().buildSessionFactory();