Spring源代码解析(八)：Spring驱动Hibernate的实现.doc

O/R工具出现之后，简化了许多复杂的信息持久化的开发。Spring应用开发者可以通过Spring提供的O/R方案更方便的使用各种持久化工具，比如Hibernate；下面我们就Spring+Hibernate中的Spring实现做一个简单的剖析。Spring对Hinberanate的配置是通过LocalSessionFactoryBean来完成的，这是一个工厂Bean的实现，在基类AbstractSessionFactoryBean中：Java代码 /* * 这是FactoryBean需要实现的接口方法，直接取得当前的sessionFactory的值 */public Object getObject() return this.sessionFactory;这个值在afterPropertySet中定义：Java代码 public void afterPropertiesSet() throws Exception /这个buildSessionFactory是通过配置信息得到SessionFactory的地方SessionFactory rawSf = buildSessionFactory();/这里使用了Proxy方法插入对getCurrentSession的拦截，得到和事务相关的sessionthis.sessionFactory = wrapSessionFactoryIfNecessary(rawSf);我们先看看SessionFactory是怎样创建的，这个方法很长，包含了创建Hibernate的SessionFactory的详尽步骤：Java代码 protected SessionFactory buildSessionFactory() throws Exception SessionFactory sf = null;/ Create Configuration instance.Configuration config = newConfiguration();/这里配置数据源，事务管理器，LobHander到Holder中，这个Holder是一个ThreadLocal变量,这样这些资源就和线程绑定了if (this.dataSource != null) / Make given DataSource available for SessionFactory configuration.configTimeDataSourceHolder.set(this.dataSource);if (this.jtaTransactionManager != null) / Make Spring-provided JTA TransactionManager available.configTimeTransactionManagerHolder.set(this.jtaTransactionManager);if (this.lobHandler != null) / Make given LobHandler available for SessionFactory configuration./ Do early because because mapping resource might refer to custom types.configTimeLobHandlerHolder.set(this.lobHandler);/这里是使用Hibernate的各个属性的配置，这里使用了Configuration类来抽象这些数据try / Set connection release mode on_close as default./ This was the case for Hibernate 3.0; Hibernate 3.1 changed/ it to auto (i.e. after_statement or after_transaction)./ However, for Springs resource management (in particular for/ HibernateTransactionManager), on_close is the better default.config.setProperty(Environment.RELEASE_CONNECTIONS, ConnectionReleaseMode.ON_CLOSE.toString();if (!isExposeTransactionAwareSessionFactory() / Not exposing a SessionFactory proxy with transaction-aware/ getCurrentSession() method - set Hibernate 3.1 CurrentSessionContext/ implementation instead, providing the Spring-managed Session that way./ Can be overridden by a custom value for corresponding Hibernate property.config.setProperty(Environment.CURRENT_SESSION_CONTEXT_CLASS,org.springframework.orm.hibernate3.SpringSessionContext);if (this.entityInterceptor != null) / Set given entity interceptor at SessionFactory level.config.setInterceptor(this.entityInterceptor);if (this.namingStrategy != null) / Pass given naming strategy to Hibernate Configuration.config.setNamingStrategy(this.namingStrategy);if (this.typeDefinitions != null) / Register specified Hibernate type definitions.Mappings mappings = config.createMappings();for (int i = 0; i this.typeDefinitions.length; i+) TypeDefinitionBean typeDef = this.typeDefinitionsi;mappings.addTypeDef(typeDef.getTypeName(), typeDef.getTypeClass(), typeDef.getParameters();if (this.filterDefinitions != null) / Register specified Hibernate FilterDefinitions.for (int i = 0; i this.filterDefinitions.length; i+) config.addFilterDefinition(this.filterDefinitionsi);if (this.configLocations != null) for (int i = 0; i this.configLocations.length; i+) / Load Hibernate configuration from given location.config.configure(this.configLocationsi.getURL();if (this.hibernateProperties != null) / Add given Hibernate properties to Configuration.config.addProperties(this.hibernateProperties);if (this.dataSource != null) boolean actuallyTransactionAware =(this.useTransactionAwareDataSource | this.dataSource instanceof TransactionAwareDataSourceProxy);/ Set Spring-provided DataSource as Hibernate ConnectionProvider.config.setProperty(Environment.CONNECTION_PROVIDER,actuallyTransactionAware ?TransactionAwareDataSourceConnectionProvider.class.getName() :LocalDataSourceConnectionProvider.class.getName();if (this.jtaTransactionManager != null) / Set Spring-provided JTA TransactionManager as Hibernate property.config.setProperty(Environment.TRANSACTION_MANAGER_STRATEGY, LocalTransactionManagerLookup.class.getName();if (this.mappingLocations != null) / Register given Hibernate mapping definitions, contained in resource files.for (int i = 0; i this.mappingLocations.length; i+) config.addInputStream(this.mappingLocationsi.getInputStream();if (this.cacheableMappingLocations != null) / Register given cacheable Hibernate mapping definitions, read from the file system.for (int i = 0; i this.cacheableMappingLocations.length; i+) config.addCacheableFile(this.cacheableMappingLocationsi.getFile();if (this.mappingJarLocations != null) / Register given Hibernate mapping definitions, contained in jar files.for (int i = 0; i this.mappingJarLocations.length; i+) Resource resource = this.mappingJarLocationsi;config.addJar(resource.getFile();if (this.mappingDirectoryLocations != null) / Register all Hibernate mapping definitions in the given directories.for (int i = 0; i 1) config.setCacheConcurrencyStrategy(className, strategyAndRegion0, strategyAndRegion1);else if (strategyAndRegion.length 0) config.setCacheConcurrencyStrategy(className, strategyAndRegion0);if (this.collectionCacheStrategies != null) / Register cache strategies for mapped collections.for (Enumeration collRoles = this.collectionCacheSpertyNames(); collRoles.hasMoreElements();) String collRole = (String) collRoles.nextElement();String strategyAndRegion =StringUmaDelimitedListToStringArray(this.collectionCacheStrategies.getProperty(collRole);if (strategyAndRegion.length 1) config.setCollectionCacheConcurrencyStrategy(collRole, strategyAndRegion0, strategyAndRegion1);else if (strategyAndRegion.length 0) config.setCollectionCacheConcurrencyStrategy(collRole, strategyAndRegion0);if (this.eventListeners != null) / Register specified Hibernate event listeners.for (Iterator it = this.eventListeners.entrySet().iterator(); it.hasNext();) Map.Entry entry = (Map.Entry) it.next();Assert.isTrue(entry.getKey() instanceof String, Event listener key needs to be of type String);String listenerType = (String) entry.getKey();Object listenerObject = entry.getValue();if (listenerObject instanceof Collection) Collection listeners = (Collection) listenerObject;EventListeners listenerRegistry = config.getEventListeners();Object listenerArray =(Object) Array.newInstance(listenerRegistry.getListenerClassFor(listenerType), listeners.size();listenerArray = listeners.toArray(listenerArray);config.setListeners(listenerType, listenerArray);else config.setListener(listenerType, listenerObject);/ Perform custom post-processing in subclasses.postProcessConfiguration(config);/ 这里是根据Configuration配置创建SessionFactory的地方(Building new Hibernate SessionFactory);this.configuration = config;sf = newSessionFactory(config);/最后把和线程绑定的资源清空finally if (this.dataSource != null) / Reset DataSource holder.configTimeDataSourceHolder.set(null);if (this.jtaTransactionManager != null) / Reset TransactionManager holder.configTimeTransactionManagerHolder.set(null);if (this.lobHandler != null) / Reset LobHandler holder.configTimeLobHandlerHolder.set(null);/ Execute schema update if requested.if (this.schemaUpdate) updateDatabaseSchema();return sf;而直接调用org.hibernate.cfg.Configuration来得到需要的SessionFactory:Java代码 protected SessionFactory newSessionFactory(Configuration config) throws HibernateException return config.buildSessionFactory();所以我们这里看到LocalSessionFactory大致起到的一个读取资源配置然后生成SessionFactory的作用；当然这里在得到 SessionFactory之后，还需要对session的事务管理作一些处理 - 使用了一个Proxy模式对getCurrentSession方法进行了拦截；Java代码 /这里先根据当前的SessionFactory的类型得到Proxy，然后插入Spring定义好的getCurrentSession拦截器protected SessionFactory getTransactionAwareSessionFactoryProxy(SessionFactory target) Class sfInterface = SessionFactory.class;if (target instanceof SessionFactoryImplementor) sfInterface = SessionFactoryImplementor.class;return (SessionFactory) Proxy.newProxyInstance(sfInterface.getClassLoader(),new Class sfInterface, new TransactionAwareInvocationHandler(target);拦截器的实现如下：Java代码 private static class TransactionAwareInvocationHandler implements InvocationHandler private final SessionFactory target;public TransactionAwareInvocationHandler(SessionFactory target) this.target = target;public Object invoke(Object proxy, Method method, Object args) throws Throwable / Invocation on SessionFactory/SessionFactoryImplementor interface coming in./ 这里对getCurrentSession方法进行拦截，得到一个和当前事务绑定的session交给用户if (method.getName().equals(getCurrentSession) / Handle getCurrentSession method: return transactional Session, if any.try return SessionFactoryUtils.doGetSession(SessionFactory) proxy, false);catch (IllegalStateException ex) throw new HibernateException(ex.getMessage();else if (method.getName().equals(equals) / Only consider equal when proxies are identical.return (proxy = args0 ? Boolean.TRUE : Boolean.FALSE);else if (method.getName().equals(hashCode) / Use hashCode of SessionFactory proxy.return new Integer(hashCode();/ 这里是需要运行的SessionFactory的目标方法try return method.invoke(this.target, args);catch (InvocationTargetException ex) throw ex.getTargetException();我们看看getCurrentSession的实现，在SessionFactoryUtils中：Java代码 private static Session doGetSession(SessionFactory sessionFactory, Interceptor entityInterceptor,SQLExceptionTranslator jdbcExceptionTranslator, boolean allowCreate)throws HibernateException, IllegalStateException Assert.notNull(sessionFactory, No SessionFactory specified);/这个TransactionSynchronizationManager的Resource是一个ThreadLocal变量,sessionFactory是一个单例，但ThreadLocal是和线程绑定的/这样就实现了Hiberante中常用的通过ThreadLocal的session管理机制SessionHolder sessionHolder = (SessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);if (sessionHolder != null & !sessionHolder.isEmpty() / pre-bound Hibernate SessionSession session = null;if (TransactionSynchronizationManager.isSynchronizationActive() &sessionHolder.doesNotHoldNonDefaultSession() / Spring transaction management is active -/ register pre-bound Session with it for transactional flushing.session = sessionHolder.getValidatedSession();if (session != null & !sessionHolder.isSynchronizedWithTransaction() logger.debug(Registering Spring transaction synchronization for existing Hibernate Session);TransactionSynchronizationManager.registerSynchronization(new SpringSessionSynchronization(sessionHolder, sessionFactory, jdbcExceptionTranslator, false);sessionHolder.setSynchronizedWithTransaction(true);/ Switch to FlushMode.AUTO, as we have to assume a thread-bound Session/ with FlushMode.NEVER, which needs to allow flushing within the transaction.FlushMode flushMode = session.getFlushMode();if (flushMode.lessThan(FlushMode.COMMIT) &!TransactionSynchronizationManager.isCurrentTransactionReadOnly() session.setFlushMode(FlushMode.AUTO);sessionHolder.setPreviousFlushMode(flushMode);else / No Spring transaction management active - try JTA transaction synchronization.session = getJtaSynchronizedSession(sessionHolder, sessionFactory, jdbcExceptionTranslator);if (session != null) return session;/这里直接打开一个Sessionlogger.debug(Opening Hibernate Session);Session session = (entityInterceptor != null ?sessionFactory.openSession(entityInterceptor) : sessionFactory.openSession();/ Use same Session for further Hibernate actions within the transaction./ Thread object will get removed by synchronization at transaction completion./ 把新打开的Session放到SessionHolder,然后放到ThreadLocal里面去和线程绑定起来，这个ThreadLocal是在 TransactionSynchronizationManager中配置好的，可以根据sessionFactory来索取/ 同时根据事务处理的状态来配置session的属性,比如把FlushMode设置为Never，同时把session和事务处理关联起来if (TransactionSynchronizationManager.isSynchronizationActive() / Were within a Spring-managed transaction, possibly from JtaTransactionManager.logger.debug(Registering Spring transaction synchronization for new Hibernate Session);SessionHolder holderToUse = sessionHolder;if (holderToUse = null) holderToUse = new SessionHolder(session);else holderToUse.addSession(session);if (TransactionSynchronizationManager.isCurrentTransactionReadOnly() session.setFlushMode(FlushMode.NEVER);TransactionSynchronizationManager.registerSynchronization(new SpringSessionSynchronization(holderToUse, sessionFactory, jdbcExceptionTranslator, true);holderToUse.setSynchronizedWithTransaction(true);if (holderToUse != sessionHolder) TransactionSynchronizationManager.bindResource(sessionFactory, holderToUse);else / No Spring transaction management active - try JTA transaction synchronization.registerJtaSynchronization(session, sessionFactory, jdbcExceptionTranslator, sessionHolder);/ Check whether we are allowed to return the Session.if (!allowCreate & !isSessionTransactional(session, sessionFactory) closeSession(session);throw new IllegalStateException(No Hibernate Session bound to thread, +and configuration does not allow creation of non-transactional one here);return session;这里就是在Spring中为使用Hiberante的SessionFactory以及Session做的准备工作，在这个基础上，用户可以通过使用 HibernateTemplate来使用Hibernate的O/R功能，和以前看到的一样这是一个execute的回调：Java代码 public Object execute(HibernateCallback action, boolean exposeNativeSession) throws DataAccessException Assert.notNull(action, Callback object must not be null);/这里得到配置好的Hibernate的SessionSession session = getSession();boolean existingTransaction = SessionFactoryUtils.isSessionTransactional(session, getSessionFactory();if (existingTransaction) logger.debug(Found thread-bound Session for HibernateTemplate);FlushMode previousFlushMode = null;try previousFlushMode = applyFlushMode(session, existingTransaction);enableFilters(session);Session sessionToExpose = (exposeNativeSession ? session : createSessionProxy(session);/这里是回调的入口Object result = action.doInHibernate(sessionToExpose);flushIfNecessary(session, existingTransaction);return result;catch (HibernateException ex) throw convertHibernateAccessException(ex);catch (SQLEx