Spring事务解析2-标签解析

Posted 2020-08-20 wade&luffy

根据自定义标签的使用规则，可以知道会执行AnnotationDrivenBeanDefinitionParser的parse

    @Override
    public BeanDefinition parse(Element element, ParserContext parserContext) {
        registerTransactionalEventListenerFactory(parserContext);
        String mode = element.getAttribute("mode");
        if ("aspectj".equals(mode)) {
            // mode="aspectj"
            registerTransactionAspect(element, parserContext);
        }
        else {
            // mode="proxy"
            AopAutoProxyConfigurer.configureAutoProxyCreator(element, parserContext);
        }
        return null;
    }

在解析中存在对于mode属性的判断，根据配置，选择以动态织入还是静态织入。以下分析以proxy方式织入。

注册InfrastructureAdvisorAutoProxyCreator

private static class AopAutoProxyConfigurer {
    public static void configureAutoProxyCreator(Element element, ParserContext parserContext) {
        AopNamespaceUtils.registerAutoProxyCreatorIfNecessary(parserContext, element);
        //TRANSACTION_ADVISOR_BEAN_NAME ="org.springframework.transaction.config.internalTransactionAdvisor";
        String txAdvisorBeanName = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME;
        if (!parserContext.getRegistry().containsBeanDefinition(txAdvisorBeanName)) {
            Object eleSource = parserContext.extractSource(element);
            //创建TransactionAttributeSource的bean
            RootBeanDefinition sourceDef = new RootBeanDefinition(
                    "org.springframework.transaction.annotation.AnnotationTransactionAttributeSource");
            sourceDef.setSource(eleSource);
            sourceDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
            //注册bean,并使用Spring中的定义规则生成beanname
            String sourceName = parserContext.getReaderContext().registerWithGeneratedName(sourceDef);
            //创建TransactionInterceptor的bean
            RootBeanDefinition interceptorDef = new RootBeanDefinition(TransactionInterceptor.class);
            interceptorDef.setSource(eleSource);
            interceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
            registerTransactionManager(element, interceptorDef);
            interceptorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
            //注册bean,并使用Spring中的定义规则生成beanname
            String interceptorName = parserContext.getReaderContext().registerWithGeneratedName(interceptorDef);
            //如果配置了order属性，则加入到bean中
            //创建TransactionAttributeSourceAdvisor的bean
            RootBeanDefinition advisorDef = new RootBeanDefinition(BeanFactoryTransactionAttributeSourceAdvisor.class);
            advisorDef.setSource(eleSource);
            advisorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
            //将sourceName的bean注入advisorDef的transactionAttributeSource属性中
            advisorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
            //将interceptorName的bean注入advisorDef的adviceBeanName属性中
            advisorDef.getPropertyValues().add("adviceBeanName", interceptorName);
            if (element.hasAttribute("order")) {
                advisorDef.getPropertyValues().add("order", element.getAttribute("order"));
            }
            parserContext.getRegistry().registerBeanDefinition(txAdvisorBeanName, advisorDef);
            //创建CompositeComponentDefinition
            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);
        }
    }
}

上面的代码注册了代理类及三个bean，这三个bean支撑了整个的事务功能，那么这三个bean是怎么组织起来的呢？

其中的两个bean被注册到了一个名为advisorDef的bean中，advisorDef使用BeanFactoryTransactionAttributeSourceAdvisor作为其class属性。也就是说BeanFactoryTransactionAttributeSourceAdvisor代表着当前bean。

上面函数configureAutoProxyCreator中的第一句貌似很简单但却是很重要的代码：

AopNamespaceUtils.registerAutoProxyCreatorIfNecessary(parserContext, element);

    public static void registerAutoProxyCreatorIfNecessary(
            ParserContext parserContext, Element sourceElement) {
        BeanDefinition beanDefinition = AopConfigUtils.registerAutoProxyCreatorIfNecessary(
                parserContext.getRegistry(), parserContext.extractSource(sourceElement));
        useClassProxyingIfNecessary(parserContext.getRegistry(), sourceElement);
        registerComponentIfNecessary(beanDefinition, parserContext);
    }

对于解析来的代码流程AOP中已经有所分析，上面的两个函数主要目的是注册了InfrastructureAdvisorAutoProxyCreator类型的bean，那么注册这个类的目的是什么呢？

    public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry, Object source) {
        return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
    }