Spring 源码详解AOP （三）

书接上回，在启动类或者配置类上使用@EnableAspectJAutoProxy开启AOP
容器会将AspectJAutoProxyRegistrar注入

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由于AspectJAutoProxyRegistrar实现了ImportBeanDefinitionRegistrar接口，所以在注册时会调用registerBeanDefinitions来注册对应的Bean
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可以看到registerBeanDefinitions最后注册的是AnnotationAwareAspectJAutoProxyCreator
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实际上AnnotationAwareAspectJAutoProxyCreator为Bean的后置处理器，由Spring 源码详解Bean创建 （二）知道在Bean创建完成初始化的前后会执行所有BeanPostProcessor的前置处理（postProcessBeforeInstantiation）和后置处理（postProcessAfterInitialization）
所以在Bean的初始化
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接下来举个例子介绍AOP的完整流程，创建BusService中divide方法为切点，看看AOP是如何将TestAspectJAnnotationProcess的方法织入到BusService中
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直接从BusService完成创建填充属性后开始初始化开始

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AnnotationAwareAspectJAutoProxyCreator前置处理直接返回不做任何处理

AnnotationAwareAspectJAutoProxyCreator开始处理后置

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public List<Advisor> buildAspectJAdvisors() {
    List<String> aspectNames = this.aspectBeanNames;

    if (aspectNames == null) {
        synchronized (this) {
            aspectNames = this.aspectBeanNames;
            if (aspectNames == null) {
                List<Advisor> advisors = new ArrayList<>();
                aspectNames = new ArrayList<>();
                //查出容器中所有的BeanName
                String[] beanNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
                        this.beanFactory, Object.class, true, false);
                for (String beanName : beanNames) {
                    if (!isEligibleBean(beanName)) {
                        continue;
                    }
                    // We must be careful not to instantiate beans eagerly as in this case they
                    // would be cached by the Spring container but would not have been weaved.
                    Class<?> beanType = this.beanFactory.getType(beanName, false);
                    if (beanType == null) {
                        continue;
                    }
                    //将带有@Aspect注解的Bean筛选出来
                    if (this.advisorFactory.isAspect(beanType)) {
                        aspectNames.add(beanName);
                        AspectMetadata amd = new AspectMetadata(beanType, beanName);
                        if (amd.getAjType().getPerClause().getKind() == PerClauseKind.SINGLETON) {
                            //创建处理带有@Aspect类的Bean工厂
                            MetadataAwareAspectInstanceFactory factory =
                                    new BeanFactoryAspectInstanceFactory(this.beanFactory, beanName);
                            //创建切面Advisor对象
                            List<Advisor> classAdvisors = this.advisorFactory.getAdvisors(factory);
                            if (this.beanFactory.isSingleton(beanName)) {
                                this.advisorsCache.put(beanName, classAdvisors);
                            }
                            else {
                                this.aspectFactoryCache.put(beanName, factory);
                            }
                            advisors.addAll(classAdvisors);
                        }
                        else {
                            // Per target or per this.
                            if (this.beanFactory.isSingleton(beanName)) {
                                throw new IllegalArgumentException("Bean with name '" + beanName +
                                        "' is a singleton, but aspect instantiation model is not singleton");
                            }
                            MetadataAwareAspectInstanceFactory factory =
                                    new PrototypeAspectInstanceFactory(this.beanFactory, beanName);
                            this.aspectFactoryCache.put(beanName, factory);
                            advisors.addAll(this.advisorFactory.getAdvisors(factory));
                        }
                    }
                }
                this.aspectBeanNames = aspectNames;
                return advisors;
            }
        }
    }

    if (aspectNames.isEmpty()) {
        return Collections.emptyList();
    }
    List<Advisor> advisors = new ArrayList<>();
    for (String aspectName : aspectNames) {
        List<Advisor> cachedAdvisors = this.advisorsCache.get(aspectName);
        if (cachedAdvisors != null) {
            advisors.addAll(cachedAdvisors);
        }
        else {
            MetadataAwareAspectInstanceFactory factory = this.aspectFactoryCache.get(aspectName);
            advisors.addAll(this.advisorFactory.getAdvisors(factory));
        }
    }
    return advisors;
}

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如下图创建完毕的代理类回调callback_0为DynamicAdvisedInterceptor类型

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IOC容器创建完成，执行业务方法，进入切点
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进入CGLIB回调
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其他几个通知节点不一一介绍，大家有兴趣可以看看源码，至此AOP代理创建以及运行时执行解析流程全部结束。