Spring声明式事务注解之@EnableTransactionManagement有什么用

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

public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> {
 
 /**
  * {@inheritDoc}
  * @return {@link ProxyTransactionManagementConfiguration} or
  * {@code AspectJTransactionManagementConfiguration} for {@code PROXY} and
  * {@code ASPECTJ} values of {@link EnableTransactionManagement#mode()}, respectively
  */
 @Override
 protected String[] selectImports(AdviceMode adviceMode) {
  switch (adviceMode) {
   case PROXY:
    // 根据@EnableTransactionManagement的固定值PROXY，这里会导入AutoProxyRegistrar组件和ProxyTransactionManagementConfiguration组件
    return new String[] {AutoProxyRegistrar.class.getName(), ProxyTransactionManagementConfiguration.class.getName()};
   case ASPECTJ:
    return new String[] {TransactionManagementConfigUtils.TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME};
   default:
    return null;
  }
 } 
}

InfrastructureAdvisorAutoProxyCreator
    --AbstractAdvisorAutoProxyCreator
        --AbstractAdvisorAutoProxyCreator
            --ProxyProcessorSupport
            --SmartInstantiationAwareBeanPostProcessor  // 跟AOP是原理是一样的
                --InstantiationAwareBeanPostProcessor
                    --BeanPostProcessor
            --BeanFactoryAware

package org.springframework.transaction.annotation; 
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Role;
import org.springframework.transaction.config.TransactionManagementConfigUtils;
import org.springframework.transaction.interceptor.BeanFactoryTransactionAttributeSourceAdvisor;
import org.springframework.transaction.interceptor.TransactionAttributeSource;
import org.springframework.transaction.interceptor.TransactionInterceptor;
 
@Configuration
public class ProxyTransactionManagementConfiguration extends AbstractTransactionManagementConfiguration {
 
	
	/** 
		事务增强器(Advisor)，在事务类创建的时候，被AutoProxyRegistrar导入的组件InfrastructureAdvisorAutoProxyCreator拦截，
		InfrastructureAdvisorAutoProxyCreator拦截的逻就是增强事务类的事务方法，	而BeanFactoryTransactionAttributeSourceAdvisor作为增强器，
		与需要增强的方法(这里是指被@Transactional标记的方法)进行匹配，匹配成功的增强器，最后转成拦截器(MethodInterceptor,
		就是下面的TransactionInterceptor)，然后与目标方法一起在拦截器链中被执行，达到方法增强的效果；
		
		
		BeanFactoryTransactionAttributeSourceAdvisor的继承关系如下：
		
		BeanFactoryTransactionAttributeSourceAdvisor
			--AbstractBeanFactoryPointcutAdvisor
				--AbstractPointcutAdvisor
					--PointcutAdvisor
						--Advisor
		
		AOP中AspectJPointcutAdvisor的继承关系如下，与AbstractPointcutAdvisor一样，都实现PointcutAdvisor
				--AspectJPointcutAdvisor
					--PointcutAdvisor
						--Advisor
	*/
	@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;
	} 
 
	/**
		@Transactional注解的解析类；负责解析事务方法上@Transactional中的各个参数配置，解析的时机是在创建事务类之后被增强的时候，
		匹配事务方法的时候一起被解析了
		
		AnnotationTransactionAttributeSource的继承关系如下：
		
		AnnotationTransactionAttributeSource
			--AbstractFallbackTransactionAttributeSource
				--TransactionAttributeSource
		通过方法org.springframework.transaction.interceptor.AbstractFallbackTransactionAttributeSource.getTransactionAttribute(Method, Class<?>)
		解析出事务信息TransactionAttribute；
		
		AnnotationTransactionAttributeSource在方法findTransactionAttribute(Class<?>)中依赖于SpringTransactionAnnotationParser在解析事务类时，
		绑定事务方法与增强器的时候进行@Transactional注解解析；
		
	*/
	@Bean
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	public TransactionAttributeSource transactionAttributeSource() {
		return new AnnotationTransactionAttributeSource();
	}
 
	/**
		被@Transactional标记的事务方法的拦截器，实际是一个MethodInterceptor
		保存了事务属性信息，事务管理器；
		在目标方法执行的时候；执行拦截器链；
	*/
	@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;
	}
}

protected TransactionAttribute parseTransactionAnnotation(AnnotationAttributes attributes) {
	RuleBasedTransactionAttribute rbta = new RuleBasedTransactionAttribute();
	Propagation propagation = attributes.getEnum("propagation");
	rbta.setPropagationBehavior(propagation.value());
	Isolation isolation = attributes.getEnum("isolation");
	rbta.setIsolationLevel(isolation.value());
	rbta.setTimeout(attributes.getNumber("timeout").intValue());
	rbta.setReadOnly(attributes.getBoolean("readOnly"));
	rbta.setQualifier(attributes.getString("value"));
	ArrayList<RollbackRuleAttribute> rollBackRules = new ArrayList<RollbackRuleAttribute>();
	Class<?>[] rbf = attributes.getClassArray("rollbackFor");
	for (Class<?> rbRule : rbf) {
		RollbackRuleAttribute rule = new RollbackRuleAttribute(rbRule);
		rollBackRules.add(rule);
	}
	String[] rbfc = attributes.getStringArray("rollbackForClassName");
	for (String rbRule : rbfc) {
		RollbackRuleAttribute rule = new RollbackRuleAttribute(rbRule);
		rollBackRules.add(rule);
	}
	Class<?>[] nrbf = attributes.getClassArray("noRollbackFor");
	for (Class<?> rbRule : nrbf) {
		NoRollbackRuleAttribute rule = new NoRollbackRuleAttribute(rbRule);
		rollBackRules.add(rule);
	}
	String[] nrbfc = attributes.getStringArray("noRollbackForClassName");
	for (String rbRule : nrbfc) {
		NoRollbackRuleAttribute rule = new NoRollbackRuleAttribute(rbRule);
		rollBackRules.add(rule);
	}
	rbta.getRollbackRules().addAll(rollBackRules);
	return rbta;
}

AutoProxyRegistrar
ProxyTransactionManagementConfiguration