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:
-
/**
-
* 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:
-
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session
-
this.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:
-
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 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[i];
-
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[i]);
-
}
-
}
-
-
if (this.configLocations != null) {
-
for (int i = 0; i < this.configLocations.length; i++) {
-
// Load Hibernate configuration from given location.
-
config.configure(this.configLocations[i].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[i].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[i].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[i];
-
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[i].getFile();
-
if (!file.isDirectory()) {
-
throw new IllegalArgumentException(
-
"Mapping directory location [" + this.mappingDirectoryLocations[i] +
-
"] 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);
-
-
// 这里是根据Configuration配置创建SessionFactory的地方
-
logger.info("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:
-
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;
-
//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:
-
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 == args[0] ? 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:
-
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 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;
-
}
-
}
-
//这里直接打开一个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()) {
-
// 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;
-
}
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:
-
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));
-
//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 (SQLException ex) {
-
throw convertJdbcAccessException(ex);
-
}
-
catch (RuntimeException ex) {
-
// 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");
-
disableFilters(session);
-
if (previousFlushMode != null) {
-
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 {
-
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:
-
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());
-
}
-
}
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。
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