在事务配置类上声明@EnableTransactionManagement注解开启事务

在事务配置类上定义数据源

在事务配置类上定义事务管理器

在相关类或者方法上使用@Transactional声明事务

代码如下：

@Configuration@EnableTransactionManagementpublic class RootConfig{ @Bean public DataSource dataSource(){ DruidDataSource dataSource = new DruidDataSource(); dataSource.setXXX(); ... return dataSource; } @Bean public PlatfromTransactionManager txManager(){ return new DataSourceTransactionManager(dataSource()); }}@Servicepublic class UserService{ @Autowired private UserRepository userRepository; @Transactional public void addUser(User user){ userRepository.save(user); }}

@EnableTransactionManagement开启事务原理解析

@EnableTransactionManagement源码如下：

@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Import(TransactionManagementConfigurationSelector.class)public @interface EnableTransactionManagement { boolean proxyTargetClass() default false; AdviceMode mode() default AdviceMode.PROXY; int order() default Ordered.LOWEST_PRECEDENCE;}

可以看到，@EnableTransactionManagement接口类主要Import了TransactionManagementConfigurationSelector来实现其注入，而TransactionManagementConfigurationSelector又主要使用selectImport方法来实现其注入，代码如下：

@Overridepublic final String[] selectImports(AnnotationMetadata importingClassMetadata) { Class<?> annoType = GenericTypeResolver.resolveTypeArgument(getClass(), AdviceModeImportSelector.class); AnnotationAttributes attributes = AnnotationConfigUtils.attributesFor(importingClassMetadata, annoType); if (attributes == null) { throw new IllegalArgumentException(String.format( "@%s is not present on importing class '%s' as expected", annoType.getSimpleName(), importingClassMetadata.getClassName())); } AdviceMode adviceMode = attributes.getEnum(this.getAdviceModeAttributeName()); //根据AdviceMode返回不同的类型，默认是AdviceMode.PROXY。 String[] imports = selectImports(adviceMode); if (imports == null) { throw new IllegalArgumentException(String.format("Unknown AdviceMode: '%s'", adviceMode)); } return imports;}@Overrideprotected String[] selectImports(AdviceMode adviceMode) { switch (adviceMode) { case PROXY: return new String[] {AutoProxyRegistrar.class.getName(), ProxyTransactionManagementConfiguration.class.getName()}; case ASPECTJ: return new String[] {TransactionManagementConfigUtils.TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME}; default: return null; }}

其中主要功能点为根据AdviceMode选择创建不同的bean，AdviceMode的默认代理方式是PROXY，jdk代理。所以返回的是AutoProxyRegistrar和ProxyTransactionManagementConfiguration。

我们先分析AutoProxyRegistrar，AutoProxyRegistrar实现了ImportBeanDefinitionRegistrar，那在创建bean的时候会调用registerBeanDefinitions方法。registerBeanDefinitions方法的实现：

@Overridepublic void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { boolean candidateFound = false; Set<String> annoTypes = importingClassMetadata.getAnnotationTypes(); for (String annoType : annoTypes) { AnnotationAttributes candidate = AnnotationConfigUtils.attributesFor(importingClassMetadata, annoType); 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; //只有@EnableTransactionManagement注解才会走到这里 if (mode == AdviceMode.PROXY) { AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry); if ((Boolean) proxyTargetClass) { AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry); return; } } } } //...}public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry, Object source) { return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);}

可以看到，它通过注册InfrastructureAdvisorAutoProxyCreator来启动Spring Aop。

接下来再看ProxyTransactionManagementConfiguration的作用，代码如下：

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

ProxyTransactionManagementConfiguration是一个配置文件，注册了三个bean，BeanFactoryTransactionAttributeSourceAdvisor、AnnotationTransactionAttributeSource、TransactionInterceptor，而这三个类分别继承Advisor、Advice和Pointcut。即切面所需组件。

总结

@EnableTransactionManagement利用AutoProxyRegistrar启动Spring Aop,使用ProxyTransactionManagementConfiguration配置对应切面部件。

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