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:
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/**
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* 这是FactoryBean需要实现的接口方法,直接取得当前的sessionFactory的值
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*/
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public Object getObject() {
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return this.sessionFactory;
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}
这个值在afterPropertySet中定义:
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public void afterPropertiesSet() throws Exception {
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//这个buildSessionFactory是通过配置信息得到SessionFactory的地方
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SessionFactory rawSf = buildSessionFactory();
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//这里使用了Proxy方法插入对getCurrentSession的拦截,得到和事务相关的session
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this.sessionFactory = wrapSessionFactoryIfNecessary(rawSf);
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}
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:
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protected SessionFactory buildSessionFactory() throws Exception {
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SessionFactory sf = null;
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// Create Configuration instance.
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Configuration config = newConfiguration();
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//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
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if (this.dataSource != null) {
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// Make given DataSource available for SessionFactory configuration.
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configTimeDataSourceHolder.set(this.dataSource);
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}
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if (this.jtaTransactionManager != null) {
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// Make Spring-provided JTA TransactionManager available.
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configTimeTransactionManagerHolder.set(this.jtaTransactionManager);
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}
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if (this.lobHandler != null) {
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// Make given LobHandler available for SessionFactory configuration.
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// Do early because because mapping resource might refer to custom types.
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configTimeLobHandlerHolder.set(this.lobHandler);
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}
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//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
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try {
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// Set connection release mode "on_close" as default.
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// This was the case for Hibernate 3.0; Hibernate 3.1 changed
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// it to "auto" (i.e. "after_statement" or "after_transaction").
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// However, for Spring's resource management (in particular for
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// HibernateTransactionManager), "on_close" is the better default.
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config.setProperty(Environment.RELEASE_CONNECTIONS, ConnectionReleaseMode.ON_CLOSE.toString());
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if (!isExposeTransactionAwareSessionFactory()) {
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// Not exposing a SessionFactory proxy with transaction-aware
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// getCurrentSession() method -> set Hibernate 3.1 CurrentSessionContext
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// implementation instead, providing the Spring-managed Session that way.
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// Can be overridden by a custom value for corresponding Hibernate property.
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config.setProperty(Environment.CURRENT_SESSION_CONTEXT_CLASS,
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"org.springframework.orm.hibernate3.SpringSessionContext");
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}
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if (this.entityInterceptor != null) {
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// Set given entity interceptor at SessionFactory level.
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config.setInterceptor(this.entityInterceptor);
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}
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if (this.namingStrategy != null) {
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// Pass given naming strategy to Hibernate Configuration.
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config.setNamingStrategy(this.namingStrategy);
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}
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if (this.typeDefinitions != null) {
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// Register specified Hibernate type definitions.
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Mappings mappings = config.createMappings();
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for (int i = 0; i < this.typeDefinitions.length; i++) {
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TypeDefinitionBean typeDef = this.typeDefinitions[i];
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mappings.addTypeDef(typeDef.getTypeName(), typeDef.getTypeClass(), typeDef.getParameters());
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}
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}
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if (this.filterDefinitions != null) {
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// Register specified Hibernate FilterDefinitions.
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for (int i = 0; i < this.filterDefinitions.length; i++) {
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config.addFilterDefinition(this.filterDefinitions[i]);
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}
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}
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if (this.configLocations != null) {
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for (int i = 0; i < this.configLocations.length; i++) {
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// Load Hibernate configuration from given location.
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config.configure(this.configLocations[i].getURL());
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}
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}
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if (this.hibernateProperties != null) {
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// Add given Hibernate properties to Configuration.
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config.addProperties(this.hibernateProperties);
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}
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if (this.dataSource != null) {
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boolean actuallyTransactionAware =
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(this.useTransactionAwareDataSource || this.dataSource instanceof TransactionAwareDataSourceProxy);
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// Set Spring-provided DataSource as Hibernate ConnectionProvider.
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config.setProperty(Environment.CONNECTION_PROVIDER,
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actuallyTransactionAware ?
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TransactionAwareDataSourceConnectionProvider.class.getName() :
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LocalDataSourceConnectionProvider.class.getName());
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}
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if (this.jtaTransactionManager != null) {
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// Set Spring-provided JTA TransactionManager as Hibernate property.
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config.setProperty(
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Environment.TRANSACTION_MANAGER_STRATEGY, LocalTransactionManagerLookup.class.getName());
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}
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if (this.mappingLocations != null) {
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// Register given Hibernate mapping definitions, contained in resource files.
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for (int i = 0; i < this.mappingLocations.length; i++) {
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config.addInputStream(this.mappingLocations[i].getInputStream());
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}
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}
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if (this.cacheableMappingLocations != null) {
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// Register given cacheable Hibernate mapping definitions, read from the file system.
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for (int i = 0; i < this.cacheableMappingLocations.length; i++) {
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config.addCacheableFile(this.cacheableMappingLocations[i].getFile());
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}
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}
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if (this.mappingJarLocations != null) {
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// Register given Hibernate mapping definitions, contained in jar files.
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for (int i = 0; i < this.mappingJarLocations.length; i++) {
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Resource resource = this.mappingJarLocations[i];
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config.addJar(resource.getFile());
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}
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}
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if (this.mappingDirectoryLocations != null) {
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// Register all Hibernate mapping definitions in the given directories.
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for (int i = 0; i < this.mappingDirectoryLocations.length; i++) {
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File file = this.mappingDirectoryLocations[i].getFile();
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if (!file.isDirectory()) {
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throw new IllegalArgumentException(
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"Mapping directory location [" + this.mappingDirectoryLocations[i] +
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"] does not denote a directory");
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}
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config.addDirectory(file);
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}
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}
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if (this.entityCacheStrategies != null) {
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// Register cache strategies for mapped entities.
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for (Enumeration classNames = this.entityCacheStrategies.propertyNames(); classNames.hasMoreElements();) {
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String className = (String) classNames.nextElement();
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String[] strategyAndRegion =
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StringUtils.commaDelimitedListToStringArray(this.entityCacheStrategies.getProperty(className));
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if (strategyAndRegion.length > 1) {
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config.setCacheConcurrencyStrategy(className, strategyAndRegion[0], strategyAndRegion[1]);
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}
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else if (strategyAndRegion.length > 0) {
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config.setCacheConcurrencyStrategy(className, strategyAndRegion[0]);
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}
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}
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}
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if (this.collectionCacheStrategies != null) {
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// Register cache strategies for mapped collections.
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for (Enumeration collRoles = this.collectionCacheStrategies.propertyNames(); collRoles.hasMoreElements();) {
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String collRole = (String) collRoles.nextElement();
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String[] strategyAndRegion =
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StringUtils.commaDelimitedListToStringArray(this.collectionCacheStrategies.getProperty(collRole));
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if (strategyAndRegion.length > 1) {
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config.setCollectionCacheConcurrencyStrategy(collRole, strategyAndRegion[0], strategyAndRegion[1]);
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}
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else if (strategyAndRegion.length > 0) {
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config.setCollectionCacheConcurrencyStrategy(collRole, strategyAndRegion[0]);
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}
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}
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}
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if (this.eventListeners != null) {
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// Register specified Hibernate event listeners.
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for (Iterator it = this.eventListeners.entrySet().iterator(); it.hasNext();) {
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Map.Entry entry = (Map.Entry) it.next();
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Assert.isTrue(entry.getKey() instanceof String, "Event listener key needs to be of type String");
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String listenerType = (String) entry.getKey();
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Object listenerObject = entry.getValue();
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if (listenerObject instanceof Collection) {
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Collection listeners = (Collection) listenerObject;
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EventListeners listenerRegistry = config.getEventListeners();
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Object[] listenerArray =
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(Object[]) Array.newInstance(listenerRegistry.getListenerClassFor(listenerType), listeners.size());
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listenerArray = listeners.toArray(listenerArray);
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config.setListeners(listenerType, listenerArray);
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}
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else {
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config.setListener(listenerType, listenerObject);
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}
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}
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}
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// Perform custom post-processing in subclasses.
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postProcessConfiguration(config);
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// 这里是根据Configuration配置创建SessionFactory的地方
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logger.info("Building new Hibernate SessionFactory");
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this.configuration = config;
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sf = newSessionFactory(config);
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}
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//最后把和线程绑定的资源清空
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finally {
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if (this.dataSource != null) {
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// Reset DataSource holder.
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configTimeDataSourceHolder.set(null);
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}
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if (this.jtaTransactionManager != null) {
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// Reset TransactionManager holder.
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configTimeTransactionManagerHolder.set(null);
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}
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if (this.lobHandler != null) {
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// Reset LobHandler holder.
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configTimeLobHandlerHolder.set(null);
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}
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}
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// Execute schema update if requested.
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if (this.schemaUpdate) {
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updateDatabaseSchema();
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}
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return sf;
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}
而直接调用org.hibernate.cfg.Configuration来得到需要的SessionFactory:
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protected SessionFactory newSessionFactory(Configuration config) throws HibernateException {
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return config.buildSessionFactory();
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}
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;
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//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
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protected SessionFactory getTransactionAwareSessionFactoryProxy(SessionFactory target) {
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Class sfInterface = SessionFactory.class;
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if (target instanceof SessionFactoryImplementor) {
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sfInterface = SessionFactoryImplementor.class;
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}
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return (SessionFactory) Proxy.newProxyInstance(sfInterface.getClassLoader(),
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new Class[] {sfInterface}, new TransactionAwareInvocationHandler(target));
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}
拦截器的实现如下:
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private static class TransactionAwareInvocationHandler implements InvocationHandler {
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private final SessionFactory target;
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public TransactionAwareInvocationHandler(SessionFactory target) {
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this.target = target;
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}
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public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
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// Invocation on SessionFactory/SessionFactoryImplementor interface coming in...
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// 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
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if (method.getName().equals("getCurrentSession")) {
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// Handle getCurrentSession method: return transactional Session, if any.
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try {
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return SessionFactoryUtils.doGetSession((SessionFactory) proxy, false);
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}
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catch (IllegalStateException ex) {
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throw new HibernateException(ex.getMessage());
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}
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}
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else if (method.getName().equals("equals")) {
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// Only consider equal when proxies are identical.
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return (proxy == args[0] ? Boolean.TRUE : Boolean.FALSE);
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}
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else if (method.getName().equals("hashCode")) {
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// Use hashCode of SessionFactory proxy.
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return new Integer(hashCode());
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}
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// 这里是需要运行的SessionFactory的目标方法
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try {
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return method.invoke(this.target, args);
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}
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catch (InvocationTargetException ex) {
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throw ex.getTargetException();
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}
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}
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}
我们看看getCurrentSession的实现,在SessionFactoryUtils中:
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private static Session doGetSession(
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SessionFactory sessionFactory, Interceptor entityInterceptor,
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SQLExceptionTranslator jdbcExceptionTranslator, boolean allowCreate)
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throws HibernateException, IllegalStateException {
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Assert.notNull(sessionFactory, "No SessionFactory specified");
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//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
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//这样就实现了Hiberante中常用的通过ThreadLocal的session管理机制
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SessionHolder sessionHolder = (SessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);
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if (sessionHolder != null && !sessionHolder.isEmpty()) {
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// pre-bound Hibernate Session
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Session session = null;
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if (TransactionSynchronizationManager.isSynchronizationActive() &&
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sessionHolder.doesNotHoldNonDefaultSession()) {
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// Spring transaction management is active ->
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// register pre-bound Session with it for transactional flushing.
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session = sessionHolder.getValidatedSession();
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if (session != null && !sessionHolder.isSynchronizedWithTransaction()) {
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logger.debug("Registering Spring transaction synchronization for existing Hibernate Session");
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TransactionSynchronizationManager.registerSynchronization(
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new SpringSessionSynchronization(sessionHolder, sessionFactory, jdbcExceptionTranslator, false));
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sessionHolder.setSynchronizedWithTransaction(true);
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// Switch to FlushMode.AUTO, as we have to assume a thread-bound Session
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// with FlushMode.NEVER, which needs to allow flushing within the transaction.
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FlushMode flushMode = session.getFlushMode();
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if (flushMode.lessThan(FlushMode.COMMIT) &&
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!TransactionSynchronizationManager.isCurrentTransactionReadOnly()) {
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session.setFlushMode(FlushMode.AUTO);
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sessionHolder.setPreviousFlushMode(flushMode);
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}
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}
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}
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else {
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// No Spring transaction management active -> try JTA transaction synchronization.
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session = getJtaSynchronizedSession(sessionHolder, sessionFactory, jdbcExceptionTranslator);
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}
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if (session != null) {
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return session;
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}
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}
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//这里直接打开一个Session
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logger.debug("Opening Hibernate Session");
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Session session = (entityInterceptor != null ?
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sessionFactory.openSession(entityInterceptor) : sessionFactory.openSession());
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// Use same Session for further Hibernate actions within the transaction.
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// Thread object will get removed by synchronization at transaction completion.
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// 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
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// 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
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if (TransactionSynchronizationManager.isSynchronizationActive()) {
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// We're within a Spring-managed transaction, possibly from JtaTransactionManager.
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logger.debug("Registering Spring transaction synchronization for new Hibernate Session");
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SessionHolder holderToUse = sessionHolder;
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if (holderToUse == null) {
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holderToUse = new SessionHolder(session);
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}
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else {
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holderToUse.addSession(session);
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}
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if (TransactionSynchronizationManager.isCurrentTransactionReadOnly()) {
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session.setFlushMode(FlushMode.NEVER);
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}
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TransactionSynchronizationManager.registerSynchronization(
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new SpringSessionSynchronization(holderToUse, sessionFactory, jdbcExceptionTranslator, true));
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holderToUse.setSynchronizedWithTransaction(true);
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if (holderToUse != sessionHolder) {
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TransactionSynchronizationManager.bindResource(sessionFactory, holderToUse);
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}
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}
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else {
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// No Spring transaction management active -> try JTA transaction synchronization.
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registerJtaSynchronization(session, sessionFactory, jdbcExceptionTranslator, sessionHolder);
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}
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// Check whether we are allowed to return the Session.
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if (!allowCreate && !isSessionTransactional(session, sessionFactory)) {
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closeSession(session);
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throw new IllegalStateException("No Hibernate Session bound to thread, " +
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"and configuration does not allow creation of non-transactional one here");
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}
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return session;
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}
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:
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public Object execute(HibernateCallback action, boolean exposeNativeSession) throws DataAccessException {
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Assert.notNull(action, "Callback object must not be null");
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//这里得到配置好的Hibernate的Session
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Session session = getSession();
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boolean existingTransaction = SessionFactoryUtils.isSessionTransactional(session, getSessionFactory());
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if (existingTransaction) {
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logger.debug("Found thread-bound Session for HibernateTemplate");
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}
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FlushMode previousFlushMode = null;
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try {
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previousFlushMode = applyFlushMode(session, existingTransaction);
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enableFilters(session);
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Session sessionToExpose = (exposeNativeSession ? session : createSessionProxy(session));
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//这里是回调的入口
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Object result = action.doInHibernate(sessionToExpose);
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flushIfNecessary(session, existingTransaction);
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return result;
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}
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catch (HibernateException ex) {
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throw convertHibernateAccessException(ex);
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}
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catch (SQLException ex) {
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throw convertJdbcAccessException(ex);
-
}
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catch (RuntimeException ex) {
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// Callback code threw application exception...
-
throw ex;
-
}
-
finally {
-
//如果这个调用的方法在一个事务当中,
-
if (existingTransaction) {
-
logger.debug("Not closing pre-bound Hibernate Session after HibernateTemplate");
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disableFilters(session);
-
if (previousFlushMode != null) {
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session.setFlushMode(previousFlushMode);
-
}
-
} //否则把Session关闭
-
else {
-
// Never use deferred close for an explicitly new Session.
-
if (isAlwaysUseNewSession()) {
-
SessionFactoryUtils.closeSession(session);
-
}
-
else {
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SessionFactoryUtils.closeSessionOrRegisterDeferredClose(session, getSessionFactory());
-
}
-
}
-
}
-
}
我们看看怎样得到对应的Session的,仍然使用了SessionFactoryUtils的方法doGetSession:
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protected Session getSession() {
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if (isAlwaysUseNewSession()) {
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return SessionFactoryUtils.getNewSession(getSessionFactory(), getEntityInterceptor());
-
}
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else if (!isAllowCreate()) {
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return SessionFactoryUtils.getSession(getSessionFactory(), false);
-
}
-
else {
-
return SessionFactoryUtils.getSession(
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getSessionFactory(), getEntityInterceptor(), getJdbcExceptionTranslator());
-
}
-
}
这样我们就可以和其他的Template那样使用Hibernate的基本功能了,使用的时候Spring已经为我们对Session的获取和关闭,事务处理的绑定做好了封装 - 从这个角度看也大大方便了用户的使用。