这一章我们来看看事务的具体参数在项目启动后，是在哪个入口加载和解析的
入口
TxNamespaceHandler类，TxNamespaceHandler类是spring-tx包的自定义解析器，在它的init方法中，有一个AnnotationDrivenBeanDefinitionParser类，
@Override
public void init() {
registerBeanDefinitionParser("advice", new TxAdviceBeanDefinitionParser());
//＜tx:annotation-driven开头的配置， Spring会使用AnnotationDrivenBeanDefinitionParser类的 parse方法进行解析
registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());
registerBeanDefinitionParser("jta-transaction-manager", new JtaTransactionManagerBeanDefinitionParser());
}
再看AnnotationDrivenBeanDefinitionParser类中的parse方法
@Override
@Nullable
public BeanDefinition parse(Element element, ParserContext parserContext) {
registerTransactionalEventListenerFactory(parserContext);
String mode = element.getAttribute("mode");
if ("aspectj".equals(mode)) {
//类型为"aspectj"
registerTransactionAspect(element, parserContext);
if (ClassUtils.isPresent("javax.transaction.Transactional", getClass().getClassLoader())) {
registerJtaTransactionAspect(element, parserContext);
}
}
else {
//类型为"proxy" 默认
AopAutoProxyConfigurer.configureAutoProxyCreator(element, parserContext);
}
return null;
}
private static class AopAutoProxyConfigurer {
public static void configureAutoProxyCreator(Element element, ParserContext parserContext) {
AopNamespaceUtils.registerAutoProxyCreatorIfNecessary(parserContext, element);
String txAdvisorBeanName = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME;
if (!parserContext.getRegistry().containsBeanDefinition(txAdvisorBeanName)) {
Object eleSource = parserContext.extractSource(element);
// Create the TransactionAttributeSource definition.
//创建TransactionAttributeSource的bean
RootBeanDefinition sourceDef = new RootBeanDefinition(
"org.springframework.transaction.annotation.AnnotationTransactionAttributeSource");
sourceDef.setSource(eleSource);
sourceDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
String sourceName = parserContext.getReaderContext().registerWithGeneratedName(sourceDef);
// Create the TransactionInterceptor definition.
//创建TransactionInterceptor的bean 后面使用TransactionInterceptor作为事务增强器实现事务的逻辑
RootBeanDefinition interceptorDef = new RootBeanDefinition(TransactionInterceptor.class);
interceptorDef.setSource(eleSource);
interceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
registerTransactionManager(element, interceptorDef);
interceptorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
String interceptorName = parserContext.getReaderContext().registerWithGeneratedName(interceptorDef);
// Create the TransactionAttributeSourceAdvisor definition.
//创建TransactionAttributeSourceAdvisor的bean
RootBeanDefinition advisorDef = new RootBeanDefinition(BeanFactoryTransactionAttributeSourceAdvisor.class);
advisorDef.setSource(eleSource);
advisorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
advisorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
advisorDef.getPropertyValues().add("adviceBeanName", interceptorName);
if (element.hasAttribute("order")) {
advisorDef.getPropertyValues().add("order", element.getAttribute("order"));
}
parserContext.getRegistry().registerBeanDefinition(txAdvisorBeanName, advisorDef);
CompositeComponentDefinition compositeDef = new CompositeComponentDefinition(element.getTagName(), eleSource);
compositeDef.addNestedComponent(new BeanComponentDefinition(sourceDef, sourceName));
compositeDef.addNestedComponent(new BeanComponentDefinition(interceptorDef, interceptorName));
compositeDef.addNestedComponent(new BeanComponentDefinition(advisorDef, txAdvisorBeanName));
parserContext.registerComponent(compositeDef);
}
}
}
一步步往下走，在configureAutoProxyCreator方法中我们目前只关注registerAutoProxyCreatorIfNecessary方法
public static void registerAutoProxyCreatorIfNecessary(
ParserContext parserContext, Element sourceElement) {
BeanDefinition beanDefinition = AopConfigUtils.registerAutoProxyCreatorIfNecessary(
parserContext.getRegistry(), parserContext.extractSource(sourceElement));
useClassProxyingIfNecessary(parserContext.getRegistry(), sourceElement);
registerComponentIfNecessary(beanDefinition, parserContext);
}
然后在AopConfigUtils.registerAutoProxyCreatorIfNecessary方法中
@Nullable
public static BeanDefinition registerAutoProxyCreatorIfNecessary(
BeanDefinitionRegistry registry, @Nullable Object source) {
return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
}
那么在registerAutoProxyCreatorIfNecessary方法中，我们能看到的是注册了一个InfrastructureAdvisorAutoProxyCreator类型的bean而已，那么属于事务关键流程的又是哪一步呢？
其实上面这一串代码流程走下来，主要往正常的bean注册的流程靠近，InfrastructureAdvisorAutoProxyCreator类继承了AbstractAdvisorAutoProxyCreator类，而AbstractAdvisorAutoProxyCreator类又继承了AbstractAutoProxyCreator类，而AbstractAutoProxyCreator类就是bean实例化的重要类，其中的postProcessAfterInitialization方法才是接下来流程的关键
@Override
public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
if (bean != null) {
// 根据给定的 bean的class和name 构建一个 key
Object cacheKey = getCacheKey(bean.getClass(), beanName);
if (this.earlyProxyReferences.remove(cacheKey) != bean) {
// 如果它适合被代理 则要封装指定 bean
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}
