【hibernate源码解析】之SessionFactory

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本文将探讨Hibernate的SessionFactory，它是构建Session实例的核心。SessionFactory通过Configuration、mapping类和Settings类实例初始化，其中Settings类解析配置文件参数。此外，还涉及到SessionFactoryObserver，用于监控SessionFactory的开启和关闭。我们将深入SessionFactoryImpl的构造方法，揭示其内部工作原理。

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SessionFactory负责构建Session实例，就像在Configuration解析中，首先给出的那段代码：

private static SessionFactory sf = null;
	
	static{
		Configuration configuration = new Configuration();
		configuration.configure("cn/huawei/config/hibernate.cfg.xml");
		configuration.addClass(Customer.class);
		sf = configuration.buildSessionFactory();
	}
configuration.buildSessionFactory()方法来返回Session的实例。那么hibernate程序是如何构建Session的实例的呢？我们从代码中找找看，当然这还是离不开Configuration这个类，还是得从这个类开始，找到buildSessionFactory()这个方法。看下面的代码： 

public SessionFactory buildSessionFactory() throws HibernateException {
		log.debug( "Preparing to build session factory with filters : " + filterDefinitions );
		secondPassCompile();
		validate();
		Environment.verifyProperties( properties );
		Properties copy = new Properties();
		copy.putAll( properties );
		PropertiesHelper.resolvePlaceHolders( copy );
		Settings settings = buildSettings( copy );

		return new SessionFactoryImpl(
				this,
				mapping,
				settings,
				getInitializedEventListeners(),
				sessionFactoryObserver
			);
	}
这个方法返回的是一个sessionFactory的实例。首先我们来分析一下这个方法，这个方法是先对property这个变量里的值进行了校验，至于怎么校验的，咱们一会儿再说，校验完了之后，程序直接返回了一个new SessionFactoryImpl(this,mapping,settings,getInitializedEventListeners(),sessionFactoryObserver);咱们看一下这个方法的原始模型：
org.hibernate.impl.SessionFactoryImpl.SessionFactoryImpl(Configuration cfg, Mapping mapping, Settings settings, EventListeners listeners, SessionFactoryObserver observer) throws HibernateException

第一个参数是Configuration类的一个实例，第二个参数是mapping类的实例（里面是持久化类的一些属性），第三个参数是Settings类的实例，它通过buildSettings这个方法将配置文件中的值给解析出来方面以后使用；第四个参数是SessionFactoryObserver类型，主要的内容是观察SessionFactory打开还是关闭的。接下来我们就进入SessionFactoryImpl这个构造方法中去看看究竟：

public SessionFactoryImpl(
			Configuration cfg,
	        Mapping mapping,
	        Settings settings,
	        EventListeners listeners,
			SessionFactoryObserver observer) throws HibernateException {
		log.info("building session factory");

		Statistics concurrentStatistics = null;
		try {
			Class concurrentStatsClass = ReflectHelper.classForName("org.hibernate.stat.ConcurrentStatisticsImpl");
			Constructor constructor = concurrentStatsClass.getConstructor(new Class[]{SessionFactoryImplementor.class});
			concurrentStatistics = (Statistics) constructor.newInstance(new Object[]{this});
			log.trace("JDK 1.5 concurrent classes present");
		} catch ( NoClassDefFoundError noJava5 ) {
			log.trace("JDK 1.5 concurrent classes missing");
		} catch (Exception noJava5) {
			log.trace("JDK 1.5 concurrent classes missing");
		}

		if (concurrentStatistics != null) {
			this.statistics = concurrentStatistics;
		} else {
			this.statistics = new StatisticsImpl(this);
		}

		if ( log.isTraceEnabled() ) {
			log.trace("Statistics initialized with " + statistics.getClass().getName());
		}

		this.properties = new Properties();
		this.properties.putAll( cfg.getProperties() );
		this.interceptor = cfg.getInterceptor();
		this.settings = settings;
		this.sqlFunctionRegistry = new SQLFunctionRegistry(settings.getDialect(), cfg.getSqlFunctions());
        this.eventListeners = listeners;
		this.observer = observer != null ? observer : new SessionFactoryObserver() {
			public void sessionFactoryCreated(SessionFactory factory) {
			}
			public void sessionFactoryClosed(SessionFactory factory) {
			}
		};

		this.filters = new HashMap();
		this.filters.putAll( cfg.getFilterDefinitions() );

		if ( log.isDebugEnabled() ) {
			log.debug("Session factory constructed with filter configurations : " + filters);
		}

		if ( log.isDebugEnabled() ) {
			log.debug(
					"instantiating session factory with properties: " + properties
			);
		}

		// Caches
		settings.getRegionFactory().start( settings, properties );

		//Generators:

		identifierGenerators = new HashMap();
		Iterator classes = cfg.getClassMappings();
		while ( classes.hasNext() ) {
			PersistentClass model = (PersistentClass) classes.next();
			if ( !model.isInherited() ) {
				IdentifierGenerator generator = model.getIdentifier().createIdentifierGenerator(
						cfg.getIdentifierGeneratorFactory(),
						settings.getDialect(),
				        settings.getDefaultCatalogName(),
				        settings.getDefaultSchemaName(),
				        (RootClass) model
				);
				identifierGenerators.put( model.getEntityName(), generator );
			}
		}


		///////////////////////////////////////////////////////////////////////
		// Prepare persisters and link them up with their cache
		// region/access-strategy

		final String cacheRegionPrefix = settings.getCacheRegionPrefix() == null ? "" : settings.getCacheRegionPrefix() + ".";

		entityPersisters = new HashMap();
		Map entityAccessStrategies = new HashMap();
		Map classMeta = new HashMap();
		classes = cfg.getClassMappings();
		while ( classes.hasNext() ) {
			final PersistentClass model = (PersistentClass) classes.next();
			model.prepareTemporaryTables( mapping, settings.getDialect() );
			final String cacheRegionName = cacheRegionPrefix + model.getRootClass().getCacheRegionName();
			// cache region is defined by the root-class in the hierarchy...
			EntityRegionAccessStrategy accessStrategy = ( EntityRegionAccessStrategy ) entityAccessStrategies.get( cacheRegionName );
			if ( accessStrategy == null && settings.isSecondLevelCacheEnabled() ) {
				final AccessType accessType = AccessType.parse( model.getCacheConcurrencyStrategy() );
				if ( accessType != null ) {
					log.trace( "Building cache for entity data [" + model.getEntityName() + "]" );
					EntityRegion entityRegion = settings.getRegionFactory().buildEntityRegion( cacheRegionName, properties, CacheDataDescriptionImpl.decode( model ) );
					accessStrategy = entityRegion.buildAccessStrategy( accessType );
					entityAccessStrategies.put( cacheRegionName, accessStrategy );
					allCacheRegions.put( cacheRegionName, entityRegion );
				}
			}
			EntityPersister cp = PersisterFactory.createClassPersister( model, accessStrategy, this, mapping );
			entityPersisters.put( model.getEntityName(), cp );
			classMeta.put( model.getEntityName(), cp.getClassMetadata() );
		}
		classMetadata = Collections.unmodifiableMap(classMeta);

		Map tmpEntityToCollectionRoleMap = new HashMap();
		collectionPersisters = new HashMap();
		Iterator collections = cfg.getCollectionMappings();
		while ( collections.hasNext() ) {
			Collection model = (Collection) collections.next();
			final String cacheRegionName = cacheRegionPrefix + model.getCacheRegionName();
			final AccessType accessType = AccessType.parse( model.getCacheConcurrencyStrategy() );
			CollectionRegionAccessStrategy accessStrategy = null;
			if ( accessType != null && settings.isSecondLevelCacheEnabled() ) {
				log.trace( "Building cache for collection data [" + model.getRole() + "]" );
				CollectionRegion collectionRegion = settings.getRegionFactory().buildCollectionRegion( cacheRegionName, properties, CacheDataDescriptionImpl.decode( model ) );
				accessStrategy = collectionRegion.buildAccessStrategy( accessType );
				entityAccessStrategies.put( cacheRegionName, accessStrategy );
				allCacheRegions.put( cacheRegionName, collectionRegion );
			}
			CollectionPersister persister = PersisterFactory.createCollectionPersister( cfg, model, accessStrategy, this) ;
			collectionPersisters.put( model.getRole(), persister.getCollectionMetadata() );
			Type indexType = persister.getIndexType();
			if ( indexType != null && indexType.isAssociationType() && !indexType.isAnyType() ) {
				String entityName = ( ( AssociationType ) indexType ).getAssociatedEntityName( this );
				Set roles = ( Set ) tmpEntityToCollectionRoleMap.get( entityName );
				if ( roles == null ) {
					roles = new HashSet();
					tmpEntityToCollectionRoleMap.put( entityName, roles );
				}
				roles.add( persister.getRole() );
			}
			Type elementType = persister.getElementType();
			if ( elementType.isAssociationType() && !elementType.isAnyType() ) {
				String entityName = ( ( AssociationType ) elementType ).getAssociatedEntityName( this );
				Set roles = ( Set ) tmpEntityToCollectionRoleMap.get( entityName );
				if ( roles == null ) {
					roles = new HashSet();
					tmpEntityToCollectionRoleMap.put( entityName, roles );
				}
				roles.add( persister.getRole() );
			}
		}
		collectionMetadata = Collections.unmodifiableMap(collectionPersisters);
		Iterator itr = tmpEntityToCollectionRoleMap.entrySet().iterator();
		while ( itr.hasNext() ) {
			final Map.Entry entry = ( Map.Entry ) itr.next();
			entry.setValue( Collections.unmodifiableSet( ( Set ) entry.getValue() ) );
		}
		collectionRolesByEntityParticipant = Collections.unmodifiableMap( tmpEntityToCollectionRoleMap );

		//Named Queries:
		namedQueries = new HashMap( cfg.getNamedQueries() );
		namedSqlQueries = new HashMap( cfg.getNamedSQLQueries() );
		sqlResultSetMappings = new HashMap( cfg.getSqlResultSetMappings() );
		imports = new HashMap( cfg.getImports() );

		// after *all* persisters and named queries are registered
		Iterator iter = entityPersisters.values().iterator();
		while ( iter.hasNext() ) {
			final EntityPersister persister = ( ( EntityPersister ) iter.next() );
			persister.postInstantiate();
			registerEntityNameResolvers( persister );

		}
		iter = collectionPersisters.values().iterator();
		while ( iter.hasNext() ) {
			final CollectionPersister persister = ( ( CollectionPersister ) iter.next() );
			persister.postInstantiate();
		}

		//JNDI + Serialization:

		name = settings.getSessionFactoryName();
		try {
			uuid = (String) UUID_GENERATOR.generate(null, null);
		}
		catch (Exception e) {
			throw new AssertionFailure("Could not generate UUID");
		}
		SessionFactoryObjectFactory.addInstance(uuid, name, this, properties);

		log.debug("instantiated session factory");

		if ( settings.isAutoCreateSchema() ) {
			new SchemaExport( cfg, settings ).create( false, true );
		}
		if ( settings.isAutoUpdateSchema() ) {
			new SchemaUpdate( cfg, settings ).execute( false, true );
		}
		if ( settings.isAutoValidateSchema() ) {
			new SchemaValidator( cfg, settings ).validate();
		}
		if ( settings.isAutoDropSchema() ) {
			schemaExport = new SchemaExport( cfg, settings );
		}

		if ( settings.getTransactionManagerLookup()!=null ) {
			log.debug("obtaining JTA TransactionManager");
			transactionManager = settings.getTransactionManagerLookup().getTransactionManager(properties);
		}
		else {
			if ( settings.getTransactionFactory().isTransactionManagerRequired() ) {
				throw new HibernateException("The chosen transaction strategy requires access to the JTA TransactionManager");
			}
			transactionManager = null;
		}

		currentSessionContext = buildCurrentSessionContext();

		if ( settings.isQueryCacheEnabled() ) {
			updateTimestampsCache = new UpdateTimestampsCache(settings, properties);
			queryCache = settings.getQueryCacheFactory()
			        .getQueryCache(null, updateTimestampsCache, settings, properties);
			queryCaches = new HashMap();
			allCacheRegions.put( updateTimestampsCache.getRegion().getName(), updateTimestampsCache.getRegion() );
			allCacheRegions.put( queryCache.getRegion().getName(), queryCache.getRegion() );
		}
		else {
			updateTimestampsCache = null;
			queryCache = null;
			queryCaches = null;
		}

		//checking for named queries
		if ( settings.isNamedQueryStartupCheckingEnabled() ) {
			Map errors = checkNamedQueries();
			if ( !errors.isEmpty() ) {
				Set keys = errors.keySet();
				StringBuffer failingQueries = new StringBuffer( "Errors in named queries: " );
				for ( Iterator iterator = keys.iterator() ; iterator.hasNext() ; ) {
					String queryName = ( String ) iterator.next();
					HibernateException e = ( HibernateException ) errors.get( queryName );
					failingQueries.append( queryName );
					if ( iterator.hasNext() ) {
						failingQueries.append( ", " );
					}
					log.error( "Error in named query: " + queryName, e );
				}
				throw new HibernateException( failingQueries.toString() );
			}
		}

		//stats
		getStatistics().setStatisticsEnabled( settings.isStatisticsEnabled() );

		// EntityNotFoundDelegate
		EntityNotFoundDelegate entityNotFoundDelegate = cfg.getEntityNotFoundDelegate();
		if ( entityNotFoundDelegate == null ) {
			entityNotFoundDelegate = new EntityNotFoundDelegate() {
				public void handleEntityNotFound(String entityName, Serializable id) {
					throw new ObjectNotFoundException( id, entityName );
				}
				public boolean isEntityNotFoundException(RuntimeException exception) {
					return ObjectNotFoundException.class.isInstance( exception );
				}
			};
		}
		this.entityNotFoundDelegate = entityNotFoundDelegate;

		// this needs to happen after persisters are all ready to go...
		this.fetchProfiles = new HashMap();
		itr = cfg.iterateFetchProfiles();
		while ( itr.hasNext() ) {
			final org.hibernate.mapping.FetchProfile mappingProfile =
					( org.hibernate.mapping.FetchProfile ) itr.next();
			final FetchProfile fetchProfile = new FetchProfile( mappingProfile.getName() );
			Iterator fetches = mappingProfile.getFetches().iterator();
			while ( fetches.hasNext() ) {
				final org.hibernate.mapping.FetchProfile.Fetch mappingFetch =
						( org.hibernate.mapping.FetchProfile.Fetch ) fetches.next();
				// resolve the persister owning the fetch
				final String entityName = getImportedClassName( mappingFetch.getEntity() );
				final EntityPersister owner = ( EntityPersister ) ( entityName == null ? null : entityPersisters.get( entityName ) );
				if ( owner == null ) {
					throw new HibernateException(
							"Unable to resolve entity reference [" + mappingFetch.getEntity()
									+ "] in fetch profile [" + fetchProfile.getName() + "]"
					);
				}

				// validate the specified association fetch
				Type associationType = owner.getPropertyType( mappingFetch.getAssociation() );
				if ( associationType == null || !associationType.isAssociationType() ) {
					throw new HibernateException( "Fetch profile [" + fetchProfile.getName() + "] specified an invalid association" );
				}

				// resolve the style
				final Fetch.Style fetchStyle = Fetch.Style.parse( mappingFetch.getStyle() );

				// then construct the fetch instance...
				fetchProfile.addFetch( new Association( owner, mappingFetch.getAssociation() ), fetchStyle );
				( ( Loadable ) owner ).registerAffectingFetchProfile( fetchProfile.getName() );
			}
			fetchProfiles.put( fetchProfile.getName(), fetchProfile );
		}

		this.observer.sessionFactoryCreated( this );
	}
看这段代码的最后一行this.observer.sessionFactoryCreated( this );通过这个SessionFactoryObserver将SessionFactory创建出来。




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