【Spring实战】----Spring事务管理配置解析

上篇说了aop的配置，并且说了Spring事务管理是基于aop的，那么Spring声明式事务的配置就有两种方式：XML配置及注解配置

不多说，直接看配置文件

一、配置文件

applicationContext-transaction.xml

注解管理事务以上都是xml配置的事务，基于注解的事务，只需配置标签，然后在Spring bean中添加@Transational注解即可实现事务管理。

二，Spring事务管理本质

Spring并不直接管理事务，而是提供多种事务管理器，他们讲事务管理的职责委托给JAT或其他持久化机制所提供的平台相关的事务实现。上述配置文件中就是利用的Hibernate事务管理器实现的Hibernate事务管理。详细信息不说，想事务属性什么的，具体可参考spring in action及spring官方文档

三、继续说下事务对getCurrentSession的影响

在Spring实战篇系列----源码解析SessionFactory及Session的管理及getCurrentSession的使用文章中说了getCurrentSession是要基于事务的，才能实现session的生命周期的管理。那么Spring的事务管理到底做了什么。

首先看事务管理器HibernateTransactionManager，它并没有做太多工作，一个空的构造函数及

/**
	 * Create a new HibernateTransactionManager instance.
	 * A SessionFactory has to be set to be able to use it.
	 * @see #setSessionFactory
	 */
	public HibernateTransactionManager() {
	}

及afterPropertiesSet()方法

@Override
	public void afterPropertiesSet() {
		if (getSessionFactory() == null) {
			throw new IllegalArgumentException("Property 'sessionFactory' is required");
		}
		if (this.entityInterceptor instanceof String && this.beanFactory == null) {
			throw new IllegalArgumentException("Property 'beanFactory' is required for 'entityInterceptorBeanName'");
		}

		// Check for SessionFactory's DataSource.
		if (this.autodetectDataSource && getDataSource() == null) {
			DataSource sfds = SessionFactoryUtils.getDataSource(getSessionFactory());
			if (sfds != null) {
				// Use the SessionFactory's DataSource for exposing transactions to JDBC code.
				if (logger.isInfoEnabled()) {
					logger.info("Using DataSource [" + sfds +
							"] of Hibernate SessionFactory for HibernateTransactionManager");
				}
				setDataSource(sfds);
			}
		}
	}

可见事务管理器的初始化并没有做太多工作。那么看事务管理对其的影响，先看调用栈

TransactionSynchronizationManager.initSynchronization() line: 269	
HibernateTransactionManager(AbstractPlatformTransactionManager).prepareSynchronization(DefaultTransactionStatus, TransactionDefinition) line: 542	
HibernateTransactionManager(AbstractPlatformTransactionManager).prepareTransactionStatus(TransactionDefinition, Object, boolean, boolean, boolean, Object) line: 513	
HibernateTransactionManager(AbstractPlatformTransactionManager).getTransaction(TransactionDefinition) line: 393	
TransactionInterceptor(TransactionAspectSupport).createTransactionIfNecessary(PlatformTransactionManager, TransactionAttribute, String) line: 426	
TransactionInterceptor(TransactionAspectSupport).invokeWithinTransaction(Method, Class, InvocationCallback) line: 275	
TransactionInterceptor.invoke(MethodInvocation) line: 96	
ReflectiveMethodInvocation.proceed() line: 179	
ExposeInvocationInterceptor.invoke(MethodInvocation) line: 92	
ReflectiveMethodInvocation.proceed() line: 179	
JdkDynamicAopProxy.invoke(Object, Method, Object[]) line: 213	
$Proxy316.getOrderById(String) line: not available	
OrderController.orderPay(String, Model) line: 84	

从调用栈可以看出，只要在连接点处配置了事务管理，首先都会走到initSynchronization()。

/**
	 * Activate transaction synchronization for the current thread.
	 * Called by a transaction manager on transaction begin.
	 * @throws IllegalStateException if synchronization is already active
	 */
	public static void initSynchronization() throws IllegalStateException {
		if (isSynchronizationActive()) {
			throw new IllegalStateException("Cannot activate transaction synchronization - already active");
		}
		logger.trace("Initializing transaction synchronization");
		synchronizations.set(new LinkedHashSet());
	}

最终会在synchronizations中set进new LinkedHashSet()，从而isSynchronizationActive()为true

/**
	 * Return if transaction synchronization is active for the current thread.
	 * Can be called before register to avoid unnecessary instance creation.
	 * @see #registerSynchronization
	 */
	public static boolean isSynchronizationActive() {
		return (synchronizations.get() != null);
	}

因此这里也就解释了上上篇留下的疑问，为什么配置了事务管理，就不会抛异常了。其实只有配置了事务，session就会在事务提交或者回滚后关闭

SessionImpl.close() line: 402	
SessionFactoryUtils.closeSession(Session) line: 167	
SpringSessionSynchronization.afterCompletion(int) line: 138	
TransactionSynchronizationUtils.invokeAfterCompletion(List, int) line: 168	
HibernateTransactionManager(AbstractPlatformTransactionManager).invokeAfterCompletion(List, int) line: 1001	
HibernateTransactionManager(AbstractPlatformTransactionManager).triggerAfterCompletion(DefaultTransactionStatus, int) line: 976	
HibernateTransactionManager(AbstractPlatformTransactionManager).processCommit(DefaultTransactionStatus) line: 806	
HibernateTransactionManager(AbstractPlatformTransactionManager).commit(TransactionStatus) line: 730	
TransactionInterceptor(TransactionAspectSupport).commitTransactionAfterReturning(TransactionAspectSupport$TransactionInfo) line: 483	
TransactionInterceptor(TransactionAspectSupport).invokeWithinTransaction(Method, Class, InvocationCallback) line: 290	
TransactionInterceptor.invoke(MethodInvocation) line: 96	
ReflectiveMethodInvocation.proceed() line: 179	
ExposeInvocationInterceptor.invoke(MethodInvocation) line: 92	
ReflectiveMethodInvocation.proceed() line: 179	
JdkDynamicAopProxy.invoke(Object, Method, Object[]) line: 213	
$Proxy316.getOrderById(String) line: not available	
OrderController.orderPayInfo(String, Model) line: 72