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Hibernate developmental JSR 317 (Java Persistence API 2.0) contracts. Used to allow incremental implementation of features on the way to full JPA 2.0 support.
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// $Id: Persistence.java 17201 2009-07-25 05:24:55Z epbernard $
// EJB3 Specification Copyright 2004-2009 Sun Microsystems, Inc.
package javax.persistence;

import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import javax.persistence.spi.LoadState;
import javax.persistence.spi.PersistenceProvider;
import javax.persistence.spi.PersistenceProviderResolverHolder;

/**
 * Bootstrap class that provides access to an EntityManagerFactory.
 */
public class Persistence {

	public static String PERSISTENCE_PROVIDER = PersistenceProvider.class.getName();

	protected static final Set providers = new HashSet();

	/**
	 * Create and return an EntityManagerFactory for the named persistence unit.
	 *
	 * @param persistenceUnitName The name of the persistence unit
	 *
	 * @return The factory that creates EntityManagers configured according to the specified persistence unit
	 */
	public static EntityManagerFactory createEntityManagerFactory(String persistenceUnitName) {
		return createEntityManagerFactory( persistenceUnitName, null );
	}

	/**
	 * Create and return an EntityManagerFactory for the named persistence unit using the given properties.
	 *
	 * @param persistenceUnitName The name of the persistence unit
	 * @param properties Additional properties to use when creating the factory. The values of these properties override
	 * any values that may have been configured elsewhere
	 *
	 * @return The factory that creates EntityManagers configured according to the specified persistence unit
	 */
	public static EntityManagerFactory createEntityManagerFactory(String persistenceUnitName, Map properties) {
		EntityManagerFactory emf = null;
		List providers = getProviders();
		for ( PersistenceProvider provider : providers ) {
			emf = provider.createEntityManagerFactory( persistenceUnitName, properties );
			if ( emf != null ) {
				break;
			}
		}
		if ( emf == null ) {
			throw new PersistenceException( "No Persistence provider for EntityManager named " + persistenceUnitName );
		}
		return emf;
	}

	private static List getProviders() {
		return PersistenceProviderResolverHolder
				.getPersistenceProviderResolver()
				.getPersistenceProviders();
	}

	/**
	 * @return Returns a PersistenceUtil instance.
	 */
	public static PersistenceUtil getPersistenceUtil() {
		return util;
	}

	private static PersistenceUtil util =
			//TODO add an Hibernate specific optimization
		new PersistenceUtil() {
			public boolean isLoaded(Object entity, String attributeName) {
				List providers = Persistence.getProviders();
				for ( PersistenceProvider provider : providers ) {
					final LoadState state = provider.isLoadedWithoutReference( entity, attributeName );
					if ( state == LoadState.UNKNOWN ) continue;
					return state == LoadState.LOADED;
				}
				for ( PersistenceProvider provider : providers ) {
					final LoadState state = provider.isLoadedWithReference( entity, attributeName );
					if ( state == LoadState.UNKNOWN ) continue;
					return state == LoadState.LOADED;
				}
				return true;
			}

			public boolean isLoaded(Object object) {
				List providers = Persistence.getProviders();
				for ( PersistenceProvider provider : providers ) {
					final LoadState state = provider.isLoaded( object );
					if ( state == LoadState.UNKNOWN ) continue;
					return state == LoadState.LOADED;
				}
				return true;
			}
		};
}