核心類

InfrastructureAdvisorAutoProxyCreator

本質是一個後置處理器，和AOP的後置處理器類似，但比AOP的使用級別低。當開啟AOP代理模式後，優先使用AOP的後置處理器。

AopConfigUtils：

/**
 * The bean name of the internally managed auto-proxy creator.
 */
//和AOP一樣都向容器注入以此為name的後置處理器，進行代理類的建立
public static final String AUTO_PROXY_CREATOR_BEAN_NAME =
      "org.springframework.aop.config.internalAutoProxyCreator";

 
/**
 * Stores the auto proxy creator classes in escalation order.
 */
//按升級的順序儲存進行代理類建立的後置處理器
private static final List<Class<?>> APC_PRIORITY_LIST = new ArrayList<Class<?>>();

/**
 * Setup the escalation list.
 */
//代理建立類後置處理器升級列表，下標越大等級越高
static {
   APC_PRIORITY_LIST.add(InfrastructureAdvisorAutoProxyCreator.
 
class);
   APC_PRIORITY_LIST.add(AspectJAwareAdvisorAutoProxyCreator.class);
   APC_PRIORITY_LIST.add(AnnotationAwareAspectJAutoProxyCreator.class);
}

原始碼跟蹤

檢視註解@EnableTransactionManagement原始碼，通過@Import匯入TransactionManagementConfigurationSelector類，在類的重寫方法中可以看到向容器注入了兩個類AutoProxyRegistrar、ProxyTransactionManagementConfiguration

AutoProxyRegistrar

用於向容器中註冊事務管理用的後置處理器

==》org.springframework.context.annotation.AutoProxyRegistrar#registerBeanDefinitions

       AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);

==》org.springframework.aop.config.AopConfigUtils#registerAutoProxyCreatorIfNecessary(org.springframework.beans.factory.support.BeanDefinitionRegistry)

==》org.springframework.aop.config.AopConfigUtils#registerAutoProxyCreatorIfNecessary(org.springframework.beans.factory.support.BeanDefinitionRegistry, java.lang.Object)

==》org.springframework.aop.config.AopConfigUtils#registerOrEscalateApcAsRequired

//此類下檢查容器中是否有name為："org.springframework.aop.config.internalAutoProxyCreator"的後置處理器bean，如果沒有則註冊，如果有則比較等級大小，若是等級大則對原beanDefination升級。例如：如果啟用了AOP則不用升級

ProxyTransactionManagementConfiguration

配置事務管理所需的管理器、引數等

@Configuration
public class ProxyTransactionManagementConfiguration extends AbstractTransactionManagementConfiguration {
//類似AOP，這裡建立了一個用於事務Advisor的Bean
   @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;
   }
//封裝事務管理配置的引數，@Transactional(..)中的引數
   @Bean
   @Role(BeanDefinition.ROLE_INFRASTRUCTURE)
   public TransactionAttributeSource transactionAttributeSource() {
      return new AnnotationTransactionAttributeSource();
   }
//封裝事務用的advice為Interceptor，並關聯上了事務管理器
// TransactionInterceptor與AOP的Interceptor一樣都繼承自MethodInterceptor
//事務管理器主要用來控制事務，commit、rollback等
   @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;
   }

}

執行時原始碼

執行時原理同AOP，對添加了@Transactional註解的類做代理，對被代理類的方法進行增強處理,執行一個攔截器鏈。跟蹤進去可以發現Interceptor chain中多了一個TransactionIntercepor。通過此Interceptor在方法前開啟事務，在方法後commit或rollback。

TransactionInterceptor

==》org.springframework.transaction.interceptor.TransactionInterceptor#invoke

==》 org.springframework.transaction.interceptor.TransactionAspectSupport#invokeWithinTransaction

// If the transaction attribute is null, the method is non-transactional.
//獲取事務相關屬性、管理器
final TransactionAttribute txAttr = getTransactionAttributeSource().getTransactionAttribute(method, targetClass);
final PlatformTransactionManager tm = determineTransactionManager(txAttr);
final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);

if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
   // Standard transaction demarcation with getTransaction and commit/rollback calls.
//開啟一個事務
   TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
   Object retVal = null;
   try {
      // This is an around advice: Invoke the next interceptor in the chain.
      // This will normally result in a target object being invoked.
//呼叫被代理類的方法     
 retVal = invocation.proceedWithInvocation();
   }
   catch (Throwable ex) {
      // target invocation exception
    //回滾事務
      completeTransactionAfterThrowing(txInfo, ex);
      throw ex;
   }
   finally {
      cleanupTransactionInfo(txInfo);
   }
    //提交事務
   commitTransactionAfterReturning(txInfo);
   return retVal;
}

流程梳理

1、 建立後置處理器InfrastructureAdvisorAutoProxyCreator

2、 建立TransactionInterceptor，加入interceptor chain。

3、 對指定後置處理器為InfrastructureAdvisorAutoProxyCreator的bean使用TransactionInterceptor進行事務處理。