Spring-事务

@EnableTransactionManagement工作原理

开启Spring事务本质上就是增加了一个Advisor，在使用@EnableTransactionManagement注解来开启Spring事务时，该注解代理的功能就是向Spring容器中添加了两个Bean

@Import(TransactionManagementConfigurationSelector.class)
public @interface EnableTransactionManagement { ... }/*** Selects which implementation of {@link AbstractTransactionManagementConfiguration}* should be used based on the value of {@link EnableTransactionManagement#mode} on the* importing {@code @Configuration} class.** @author Chris Beams* @author Juergen Hoeller* @since 3.1* @see EnableTransactionManagement* @see ProxyTransactionManagementConfiguration* @see TransactionManagementConfigUtils#TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME* @see TransactionManagementConfigUtils#JTA_TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME*/
public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> {/*** Returns {@link ProxyTransactionManagementConfiguration} or* {@code AspectJ(Jta)TransactionManagementConfiguration} for {@code PROXY}* and {@code ASPECTJ} values of {@link EnableTransactionManagement#mode()},* respectively.*/@Overrideprotected String[] selectImports(AdviceMode adviceMode) {switch (adviceMode) {case PROXY:// 默认是PROXYreturn new String[] {AutoProxyRegistrar.class.getName(),ProxyTransactionManagementConfiguration.class.getName()};case ASPECTJ:// 表示不用动态代理技术，用ASPECTJ技术，一般用不到return new String[] {determineTransactionAspectClass()};default:return null;}}private String determineTransactionAspectClass() {return (ClassUtils.isPresent("javax.transaction.Transactional", getClass().getClassLoader()) ?TransactionManagementConfigUtils.JTA_TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME :TransactionManagementConfigUtils.TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME);}}

1、AutoProxyRegistrar

向Spring容器中注册了一个InfrastructureAdvisorAutoProxyCreator的Bean

InfrastructureAdvisorAutoProxyCreator 继承了AbstractAdvisorAutoProxyCreator

主要作用：开启自动代理

在初始化后寻找Advisor类型的Bean，并检查当前Bean是否有匹配的Advisor，是否需要动态代理创建代理对象

/*** Registers an auto proxy creator against the current {@link BeanDefinitionRegistry}* as appropriate based on an {@code @Enable*} annotation having {@code mode} and* {@code proxyTargetClass} attributes set to the correct values.** @author Chris Beams* @since 3.1* @see org.springframework.cache.annotation.EnableCaching* @see org.springframework.transaction.annotation.EnableTransactionManagement*/
public class AutoProxyRegistrar implements ImportBeanDefinitionRegistrar {private final Log logger = LogFactory.getLog(getClass());/*** Register, escalate, and configure the standard auto proxy creator (APC) against the* given registry. Works by finding the nearest annotation declared on the importing* {@code @Configuration} class that has both {@code mode} and {@code proxyTargetClass}* attributes. If {@code mode} is set to {@code PROXY}, the APC is registered; if* {@code proxyTargetClass} is set to {@code true}, then the APC is forced to use* subclass (CGLIB) proxying.* <p>Several {@code @Enable*} annotations expose both {@code mode} and* {@code proxyTargetClass} attributes. It is important to note that most of these* capabilities end up sharing a {@linkplain AopConfigUtils#AUTO_PROXY_CREATOR_BEAN_NAME* single APC}. For this reason, this implementation doesn't "care" exactly which* annotation it finds -- as long as it exposes the right {@code mode} and* {@code proxyTargetClass} attributes, the APC can be registered and configured all* the same.*/@Overridepublic void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {boolean candidateFound = false;Set<String> annTypes = importingClassMetadata.getAnnotationTypes();for (String annType : annTypes) {AnnotationAttributes candidate = AnnotationConfigUtils.attributesFor(importingClassMetadata, annType);if (candidate == null) {continue;}Object mode = candidate.get("mode");Object proxyTargetClass = candidate.get("proxyTargetClass");if (mode != null && proxyTargetClass != null && AdviceMode.class == mode.getClass() &&Boolean.class == proxyTargetClass.getClass()) {candidateFound = true;if (mode == AdviceMode.PROXY) {// 注册InfrastructureAdvisorAutoProxyCreator，才可以Bean进行AOPAopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);if ((Boolean) proxyTargetClass) {// 设置InfrastructureAdvisorAutoProxyCreator的proxyTargetClass为trueAopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);return;}}}}if (!candidateFound && logger.isInfoEnabled()) {String name = getClass().getSimpleName();logger.info(String.format("%s was imported but no annotations were found " +"having both 'mode' and 'proxyTargetClass' attributes of type " +"AdviceMode and boolean respectively. This means that auto proxy " +"creator registration and configuration may not have occurred as " +"intended, and components may not be proxied as expected. Check to " +"ensure that %s has been @Import'ed on the same class where these " +"annotations are declared; otherwise remove the import of %s " +"altogether.", name, name, name));}}}// AopConfigUtils#registerAutoProxyCreatorIfNecessary
public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry) {return registerAutoProxyCreatorIfNecessary(registry, null);
}// AopConfigUtils#registerAutoProxyCreatorIfNecessary
public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry, @Nullable Object source) {return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
}// AopConfigUtils#forceAutoProxyCreatorToUseClassProxying
public static void forceAutoProxyCreatorToUseClassProxying(BeanDefinitionRegistry registry) {// AUTO_PROXY_CREATOR_BEAN_NAME = "org.springframework.aop.config.internalAutoProxyCreator"if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {BeanDefinition definition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);definition.getPropertyValues().add("proxyTargetClass", Boolean.TRUE);}
}

2、ProxyTransactionManagementConfiguration

是一个配置类，内部定义了三个Bean：

BeanFactoryTransactionAttributeSourceAdvisor：一个Advisor

AnnotationTransactionAttributeSource：相当于BeanFactoryTransactionAttributeSourceAdvisor中的Pointcut，判断某个类或者方法上面是否存在@Transactional注解，注意这里并没有解析

TransactionInterceptor：相当于BeanFactoryTransactionAttributeSourceAdvisor中的 Advice，当某个类中存在@Transactional注解，就会产生一个代理对象作为Bean，在执行代理对象的某个方法时会进入到TransactionInterceptor的invoke()方法中

invoke()方法里面就会创建数据库连接、关闭自动提交、事务提交和回滚等

/*** {@code @Configuration} class that registers the Spring infrastructure beans* necessary to enable proxy-based annotation-driven transaction management.** @author Chris Beams* @author Sebastien Deleuze* @since 3.1* @see EnableTransactionManagement* @see TransactionManagementConfigurationSelector*/
@Configuration(proxyBeanMethods = false)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
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.<Integer>getNumber("order"));}return advisor;}@Bean@Role(BeanDefinition.ROLE_INFRASTRUCTURE)public TransactionAttributeSource transactionAttributeSource() {// AnnotationTransactionAttributeSource中定义了一个Pointcut// 并且AnnotationTransactionAttributeSource可以用来解析@Transactional注解，并得到一个RuleBasedTransactionAttribute对象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;}}