spring声明式事务@Transactional底层工作原理

@Override
	@Nullable
	public TransactionAttribute parseTransactionAnnotation(AnnotatedElement element) {
		AnnotationAttributes attributes = AnnotatedElementUtils.findMergedAnnotationAttributes(
				element, Transactional.class, false, false);
		if (attributes != null) {
			return parseTransactionAnnotation(attributes);
		}
		else {
			return null;
		}
	}

public boolean matches(Method method, Class targetClass) {
		TransactionAttributeSource tas = getTransactionAttributeSource();
		return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
	}

public Object invoke(MethodInvocation invocation) throws Throwable {
		// Work out the target class: may be {@code null}.
		// The TransactionAttributeSource should be passed the target class
		// as well as the method, which may be from an interface.
		Class targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);
		// Adapt to TransactionAspectSupport's invokeWithinTransaction...
		return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);
	}

@Configuration(proxyBeanMethods = false)
public class ProxyTransactionManagementConfiguration extends AbstractTransactionManagementConfiguration {
	@Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor(
			TransactionAttributeSource transactionAttributeSource,
			TransactionInterceptor transactionInterceptor) {
		BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();
		advisor.setTransactionAttributeSource(transactionAttributeSource);
		advisor.setAdvice(transactionInterceptor);
		if (this.enableTx != null) {
			advisor.setOrder(this.enableTx.getNumber("order"));
		}
		return advisor;
	}
	@Bean
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	public TransactionAttributeSource transactionAttributeSource() {
		return new AnnotationTransactionAttributeSource();
	}
	@Bean
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	public TransactionInterceptor transactionInterceptor(
			TransactionAttributeSource transactionAttributeSource) {
		TransactionInterceptor interceptor = new TransactionInterceptor();
		interceptor.setTransactionAttributeSource(transactionAttributeSource);
		if (this.txManager != null) {
			interceptor.setTransactionManager(this.txManager);
		}
		return interceptor;
	}
}

public interface PlatformTransactionManager extends TransactionManager {
	TransactionStatus getTransaction(@Nullable TransactionDefinition definition)
			throws TransactionException;
	void commit(TransactionStatus status) throws TransactionException;
	void rollback(TransactionStatus status) throws TransactionException;
}

protected PlatformTransactionManager determineTransactionManager(@Nullable TransactionAttribute txAttr) {
		// Do not attempt to lookup tx manager if no tx attributes are set
		if (txAttr == null || this.beanFactory == null) {
			return asPlatformTransactionManager(getTransactionManager());
		}
		String qualifier = txAttr.getQualifier();
		if (StringUtils.hasText(qualifier)) {
			return determineQualifiedTransactionManager(this.beanFactory, qualifier);
		}
		else if (StringUtils.hasText(this.transactionManagerBeanName)) {
			return determineQualifiedTransactionManager(this.beanFactory, this.transactionManagerBeanName);
		}
		else {
			PlatformTransactionManager defaultTransactionManager = asPlatformTransactionManager(getTransactionManager());
			if (defaultTransactionManager == null) {
				defaultTransactionManager = asPlatformTransactionManager(
						this.transactionManagerCache.get(DEFAULT_TRANSACTION_MANAGER_KEY));
				if (defaultTransactionManager == null) {
					defaultTransactionManager = this.beanFactory.getBean(PlatformTransactionManager.class);
					this.transactionManagerCache.putIfAbsent(
							DEFAULT_TRANSACTION_MANAGER_KEY, defaultTransactionManager);
				}
			}
			return defaultTransactionManager;
		}
	}