@Transactional

嵌套事務須要jdbc driver的支持！

org.springframework.transaction.NestedTransactionNotSupportedException: Cannot create a nested transaction because savepoints are not supported by your JDBC driver
	at org.springframework.jdbc.datasource.JdbcTransactionObjectSupport.createSavepoint(JdbcTransactionObjectSupport.java:106)
	at org.springframework.transaction.support.AbstractTransactionStatus.createAndHoldSavepoint(AbstractTransactionStatus.java:144)
	at org.springframework.transaction.support.AbstractPlatformTransactionManager.handleExistingTransaction(AbstractPlatformTransactionManager.java:458)
	at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:349)
	at org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:447)
	at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:277)
	at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:673)

事務回滾默認是RuntimeException 和Error

@Transactional默認RuntimeException 與 Error 類型回滾， 因此須要手動指定rollbackFor=Exception.class。

TransactionInterceptor  extends TransactionAspectSupport implements MethodInterceptor, Serializable

TransactionAspectSupport  implements BeanFactoryAware, InitializingBean

DefaultTransactionAttribute  extends DefaultTransactionDefinition implements TransactionAttribute