Spring 與hibernate 的結合

O/R工具出現之後，簡化了許多複雜的信息持久化的開發。Spring應用開發者可以通過Spring提供的O/R方案更方便的使用各種持久化工具，比如Hibernate；下面我們就Spring+Hibernate中的Spring實現做一個簡單的剖析。 Spring對Hinberanate的配置是通過LocalSessionFactoryBean來完成的，這是一個工廠Bean的實現，在基類 AbstractSessionFactoryBean中：

/**
* 這是FactoryBean需要實現的接口方法，直接取得當前的sessionFactory的值
*/
public Object getObject() {
return this.sessionFactory;
}

這個值在afterPropertySet中定義：

public void afterPropertiesSet() throws Exception {
//這個buildSessionFactory是通過配置信息得到SessionFactory的地方
SessionFactory rawSf = buildSessionFactory();
//這裏使用了Proxy方法插入對getCurrentSession的攔截，得到和事務相關的session
this.sessionFactory = wrapSessionFactoryIfNecessary(rawSf);
}

我們先看看SessionFactory是怎樣創建的，這個方法很長，包含了創建Hibernate的SessionFactory的詳盡步驟：

protected SessionFactory buildSessionFactory() throws Exception {
SessionFactory sf = null;
// Create Configuration instance.
Configuration config = newConfiguration();
//這裏配置數據源，事務管理器，LobHander到Holder中，這個Holder是一個ThreadLocal變量,這樣這些資源就和線程綁定了
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);
}
//這裏是使用Hibernate的各個屬性的配置，這裏使用了Configuration類來抽象這些數據
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 Spring's 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.typeDefinitions;
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.filterDefinitions);
}
}
if (this.configLocations != null) {
for (int i = 0; i < this.configLocations.length; i++) {
// Load Hibernate configuration from given location.
config.configure(this.configLocations.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.mappingLocations.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.cacheableMappingLocations.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.mappingJarLocations;
config.addJar(resource.getFile());
}
}
if (this.mappingDirectoryLocations != null) {
// Register all Hibernate mapping definitions in the given directories.
for (int i = 0; i < this.mappingDirectoryLocations.length; i++) {
File file = this.mappingDirectoryLocations.getFile();
if (!file.isDirectory()) {
throw new IllegalArgumentException(
"Mapping directory location [" + this.mappingDirectoryLocations +
"] does not denote a directory");
}
config.addDirectory(file);
}
}
if (this.entityCacheStrategies != null) {
// Register cache strategies for mapped entities.
for (Enumeration classNames = this.entityCacheStrategies.propertyNames(); classNames.hasMoreElements();) {
String className = (String) classNames.nextElement();
String[] strategyAndRegion =
StringUtils.commaDelimitedListToStringArray(this.entityCacheStrategies.getProperty(className));
if (strategyAndRegion.length > 1) {
config.setCacheConcurrencyStrategy(className, strategyAndRegion[0], strategyAndRegion[1]);
}
else if (strategyAndRegion.length > 0) {
config.setCacheConcurrencyStrategy(className, strategyAndRegion[0]);
}
}
}
if (this.collectionCacheStrategies != null) {
// Register cache strategies for mapped collections.
for (Enumeration collRoles = this.collectionCacheStrategies.propertyNames(); collRoles.hasMoreElements();) {
String collRole = (String) collRoles.nextElement();
String[] strategyAndRegion =
StringUtils.commaDelimitedListToStringArray(this.collectionCacheStrategies.getProperty(collRole));
if (strategyAndRegion.length > 1) {
config.setCollectionCacheConcurrencyStrategy(collRole, strategyAndRegion[0], strategyAndRegion[1]);
}
else if (strategyAndRegion.length > 0) {
config.setCollectionCacheConcurrencyStrategy(collRole, strategyAndRegion[0]);
}
}
}
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);
// 這裏是根據Configuration配置創建SessionFactory的地方
logger.info("Building new Hibernate SessionFactory");
this.configuration = config;
sf = newSessionFactory(config);
}
//最後把和線程綁定的資源清空
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;
}

而直接調用org.hibernate.cfg.Configuration來得到需要的SessionFactory:

protected SessionFactory newSessionFactory(Configuration config) throws HibernateException {
return config.buildSessionFactory();
}

所以我們這裏看到LocalSessionFactory大致起到的一個讀取資源配置然後生成SessionFactory的作用；當然這裏在得到 SessionFactory之後，還需要對session的事務管理作一些處理 -使用了一個Proxy模式對getCurrentSession方法進行了攔截；

//這裏先根據當前的SessionFactory的類型得到Proxy，然後插入Spring定義好的getCurrentSession攔截器
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));
}

攔截器的實現如下：

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...
// 這裏對getCurrentSession方法進行攔截，得到一個和當前事務綁定的session交給用戶
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 == args[0] ? Boolean.TRUE : Boolean.FALSE);
}
else if (method.getName().equals("hashCode")) {
// Use hashCode of SessionFactory proxy.
return new Integer(hashCode());
}
// 這裏是需要運行的SessionFactory的目標方法
try {
return method.invoke(this.target, args);
}
catch (InvocationTargetException ex) {
throw ex.getTargetException();
}
}
}

我們看看getCurrentSession的實現，在SessionFactoryUtils中：

private static Session doGetSession(
SessionFactory sessionFactory, Interceptor entityInterceptor,
SQLExceptionTranslator jdbcExceptionTranslator, boolean allowCreate)
throws HibernateException, IllegalStateException {
Assert.notNull(sessionFactory, "No SessionFactory specified");
//這個TransactionSynchronizationManager的Resource是一個ThreadLocal變量,sessionFactory是一個單例，但ThreadLocal是和線程綁定的
//這樣就實現了Hiberante中常用的通過ThreadLocal的session管理機制
SessionHolder sessionHolder = (SessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);
if (sessionHolder != null && !sessionHolder.isEmpty()) {
// pre-bound Hibernate Session
Session 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;
}
}
//這裏直接打開一個Session
logger.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.
// 把新打開的Session放到SessionHolder,然後放到ThreadLocal裏面去和線程綁定起來，這個ThreadLocal是在 TransactionSynchronizationManager中配置好的，可以根據sessionFactory來索取
// 同時根據事務處理的狀態來配置session的屬性,比如把FlushMode設置爲Never，同時把session和事務處理關聯起來
if (TransactionSynchronizationManager.isSynchronizationActive()) {
// We're 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;
}

這裏就是在Spring中爲使用Hiberante的SessionFactory以及Session做的準備工作，在這個基礎上，用戶可以通過使用 HibernateTemplate來使用Hibernate的O/R功能，和以前看到的一樣這是一個execute的回調：

public Object execute(HibernateCallback action, boolean exposeNativeSession) throws DataAccessException {
Assert.notNull(action, "Callback object must not be null");
//這裏得到配置好的Hibernate的Session
Session 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));
//這裏是回調的入口
Object result = action.doInHibernate(sessionToExpose);
flushIfNecessary(session, existingTransaction);
return result;
}
catch (HibernateException ex) {
throw convertHibernateAccessException(ex);
}
catch (SQLException ex) {
throw convertJdbcAccessException(ex);
}
catch (RuntimeException ex) {
// Callback code threw application exception...
throw ex;
}
finally {
//如果這個調用的方法在一個事務當中，
if (existingTransaction) {
logger.debug("Not closing pre-bound Hibernate Session after HibernateTemplate");
disableFilters(session);
if (previousFlushMode != null) {
session.setFlushMode(previousFlushMode);
}
} //否則把Session關閉
else {
// Never use deferred close for an explicitly new Session.
if (isAlwaysUseNewSession()) {
SessionFactoryUtils.closeSession(session);
}
else {
SessionFactoryUtils.closeSessionOrRegisterDeferredClose(session, getSessionFactory());
}
}
}
}

我們看看怎樣得到對應的Session的，仍然使用了SessionFactoryUtils的方法doGetSession:

protected Session getSession() {
if (isAlwaysUseNewSession()) {
return SessionFactoryUtils.getNewSession(getSessionFactory(), getEntityInterceptor());
}
else if (!isAllowCreate()) {
return SessionFactoryUtils.getSession(getSessionFactory(), false);
}
else {
return SessionFactoryUtils.getSession(
getSessionFactory(), getEntityInterceptor(), getJdbcExceptionTranslator());
}
}

這樣我們就可以和其他的Template那樣使用Hibernate的基本功能了，使用的時候Spring已經爲我們對Session的獲取和關閉，事務處理的綁定做好了封裝 - 從這個角度看也大大方便了用戶的使用。

Spring的事務管理器簡介

Spring並不直接管理事務，事實上，它是提供事務的多方選擇。你能委託事務的職責給一個特定的平臺實現，比如用JTA或者是別的持久機制。Spring的事務管理器可以用下表表示：

事務管理器的實例	目標
Org.springframwork.jdbc.datasource.DataSourceTransactionManager	用DBC的 DataSource 去管理事務
Org.springframwork.orm.hibernate.HibernateTransactionManager	當持久機制是Hibernate時的事務管理器
Org.springframework.orm.jdoTransactionManager	當持久機制是JDO時的事務管理器
Org.springframework.transaction.jta.JtaTransactionManager	用JTA管理事務
Org.springframwork.orm.ojb.PersistenceBrokerTransactionManager	當持久機制是apache的OJB時的事務管理器

所有的事務管理器就像是特別平臺的代理商。爲了使用事務管理器，我們應該在上下文中申明它。現在，我們將會看看如何去申明這些事務管理器，以DataSourceTransactionManager爲例開始

3．1 JDBC事務

如果你直接使用JDBC作爲持久方案，DataSourceTransactionManager將會爲你管理事務的邊界。爲了能使用DataSourceTransactionManager，我們把下面的XML加到上下文的定義中： <bean id="transactionManager" class="org.springframework.jdbc. Datasource.DataSourceTransactionManager"> <property name="dataSource"> <ref bean="dataSource"/> </property> </bean> 注意：dataSource的屬性設置引用一個叫dataSource的BEAN，dataSource可能是一個 javax.sql.DataSource bean，它在上下文中已經定義好了。

3．2 Hibernate事務

如果你使用Hibernate作爲持久層，你將會使用 HibernateTransactionManager，請在應用的上下文申明如下： <bean id="transactionManaager" class="org.springframework. Orm.hibernate.HibernateTransactionManager"> <property name="sessionFactory"> <ref bean="sessionFactory"/> </property> </bean> sessionFacoty 的屬性和Hibernate的SessionFactory組合在一塊兒。HibernateTransactionManager委託事務管理給一個 net.sf.hibernate.Transactioin事例，它從Hibernate的會話中獲得。當一個事務成功結束時，HibernateTransactionManager會調用Transaction的commit()方法。相似的，一個失敗的事務將會調用 rollback()去回滾。

3．3 JDO事務

可能你不喜歡JDBC 和Hibernate，你可以選擇JDO去實現你的持久層。如果是這樣的話，你可以用JdoTransctionManager，你可以在你的上下文中如下申明： <bean id="transactionManager" Class="org.springframework.orm.jdo.JdoTransactioinManager:> <property name="persistenceManagerFactory"> <ref bean="persistenceManagerFactory"/> </property> </bean> 爲了使用JdoTransctionManager，你需要組合一個具有persistenceManagerFactory 屬性的javax.jdo.PersistenceManagerFactory。其實，JdoTransactionManager和事務對象一起工作，它是從JDO的持久管理器中獲得。一個成功的事務會調用commit()方法，而一個失敗的事務會調用rollback()方法。

3．4 JTA事務:

如果你上面所有的事務管理器都不符合你的需要,,或者你的應用是多資源交錯的事務,那麼.你可以使用JTA的事務管理器 <bean id="transactionManager" class="org.springframewrok.. Transaction.jtaTransactionmanager"> <property name="transactionManager"> <value>java:/TransactionManager</valure> </property> </bean> JtaTransactionManager 委託事務管理給JTA的實現.JTA定義了一系列的標準接口;能協調事務,應用和一個或多個數據源. 在這之中, transactioinManageName屬性指向JTA事務管理器. 這個事務管理器能在JNDI中找到. JtaTransactionManager, javax.transaction.UserTransaction和javax.transaction.TransactionManager對象在一起工作. 所有的事務管理委託給它們完成. 一個成功的事務將會被提交,通過調用UserTransaction.commit()方法,相反,一個失敗的事務會調用UserTransaction 的rollback()方法.

現在.我們能找到合適的spring的事務管理器給我們的應用需要.並在配置文件中配置.現在就讓我們的事務管理器工作.在下面的章節中,我會介紹如何用申明式事務.

在Liferay中，涉及到的配置文件就是data-source-spring.xml 中的bean liferaySessionFactory，對應的class爲 com.liferay.portal.spring.hibernate.HibernateConfiguration

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