Spring Aop 源碼分析

spring aop源碼分析

前言：

正常流程
前置通知 --> 業務 --> 後置通知
異常流程：
前置通知 --> 業務 --> 後置通知 -> 異常通知

重點

看aop源碼之前必須先分析源碼的流程是怎麼樣的。

aop如何加載到spring容器

他又兩種方式啓動:
第一種
xml是一種方式–>>>> 他是如何解析xml —（看到dubbo的源碼就知道通過擴展spring提供自定義接口NamespaceHandler 重寫init方法）
第二中方式
annotaiton的方式 @EnableAspectJAutoProxy --> @Import(AspectJAutoProxyRegistrar.class) #registerBeanDefinitions 方法也是spring提供的擴展接口。
aop是如何攔截bean。

流程分析：

將bean導入spring容器AspectJAutoProxyRegistrar->ImportBeanDefinitionRegistrar#registerBeanDefinitions
將bean註冊到spring容器 AnnotationAwareAspectJAutoProxyCreator className： org.springframework.aop.config.internalAutoProxyCreator class: 根據spring提供的規範構建spring bean RootBeanDefinition
上面構建 AnnotationAwareAspectJAutoProxyCreator 這個bean 然後這個bean實現InstantiationAwareBeanPostProcessor接口
該接口實現BeanPostProcessor接口 BeanPostProcessor是spring提供的擴展接口在bean實例的時候回調 --》postProcessAfterInitialization
然後就會找所有的Advisor
1、第一步：先找父類時候有實現Advisor的接口。
2、第二步：然後找到所有類上面註解標註爲@Aspect, 然後解析該類標註Pointcut.class, Around.class, Before.class, After.class, AfterReturning.class, AfterThrowing.class

org.springframework.aop.config.AopNamespaceHandler

@Override
	public void init() {
		// In 2.0 XSD as well as in 2.1 XSD.
		// 第一步： 註冊解析bean
		registerBeanDefinitionParser("config", new ConfigBeanDefinitionParser());
		// 第二步: aspectj-autoproxy  AspectJAutoProxyBeanDefinitionParser
		registerBeanDefinitionParser("aspectj-autoproxy", new AspectJAutoProxyBeanDefinitionParser());
		registerBeanDefinitionDecorator("scoped-proxy", new ScopedProxyBeanDefinitionDecorator());

		// Only in 2.0 XSD: moved to context namespace as of 2.1
		registerBeanDefinitionParser("spring-configured", new SpringConfiguredBeanDefinitionParser());
}

org.springframework.aop.config.AspectJAutoProxyBeanDefinitionParser

public BeanDefinition parse(Element element, ParserContext parserContext) {
		// 看名字應該註冊什麼東西... 繼續分析
		AopNamespaceUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(parserContext, element);
		extendBeanDefinition(element, parserContext);
		return null;
}

org.springframework.aop.config.AopNamespaceUtils#registerAspectJAnnotationAutoProxyCreatorIfNecessary

	public static void registerAspectJAnnotationAutoProxyCreatorIfNecessary(
			ParserContext parserContext, Element sourceElement) {

		BeanDefinition beanDefinition = AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(
				parserContext.getRegistry(), parserContext.extractSource(sourceElement));
		// 對於proxy-target-class 已經 expose-proxy屬性的處理			
		useClassProxyingIfNecessary(parserContext.getRegistry(), sourceElement);
		// 註冊組件並通知，便於監聽器做進一步處理			
		registerComponentIfNecessary(beanDefinition, parserContext);
	}

總結：看完上面這個方法主要乾了一下幾件事情

註冊與升級
屬性的處理
通知

下面開始重點分析對以上三件事情做詳細分析

註冊於與升級

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

public static BeanDefinition registerAspectJAnnotationAutoProxyCreatorIfNecessary(
			BeanDefinitionRegistry registry, @Nullable Object source) {
        //  從命名的角度推測。註冊或者升級aspectJS做爲必須的。
		return registerOrEscalateApcAsRequired(AnnotationAwareAspectJAutoProxyCreator.class, registry, source);
	}

org.springframework.aop.config.AopConfigUtils#registerOrEscalateApcAsRequired

/**
參數分析
   cls 需要註冊的class
  registry： bean容器的註冊中心
   source ： xml解析完的 the source object to store   

*/
private static BeanDefinition registerOrEscalateApcAsRequired(
         
			Class<?> cls, BeanDefinitionRegistry registry, @Nullable Object source) {

		Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
         //org.springframework.aop.config.internalAutoProxyCreator 
        // 第一步： 判斷容器中是否有該類、
        //     Check if this registry contains a bean definition with the given name.
		 // 根據上面的註釋可以說明 通過beanName判斷該容器中是否存在該bean的實例對象。
		if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {
		    // 獲取實例對象
			BeanDefinition apcDefinition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);
		    // 這個判斷說明了兩個問題
		    // 容器中存在且與當前bean不一致的情況
		    // 判斷先使用哪一個的問題
			if (!cls.getName().equals(apcDefinition.getBeanClassName())) {
			    // 比較優先級   findPriorityForClass 繼續跟蹤這部分源碼發現他採用了List作爲容器，並排序。所有
			    //返回下標      
				int currentPriority = findPriorityForClass(apcDefinition.getBeanClassName());
				int requiredPriority = findPriorityForClass(cls);
				if (currentPriority < requiredPriority) {
					apcDefinition.setBeanClassName(cls.getName());
				}
			}
			return null;
		}

		RootBeanDefinition beanDefinition = new RootBeanDefinition(cls);
		beanDefinition.setSource(source);
		beanDefinition.getPropertyValues().add("order", Ordered.HIGHEST_PRECEDENCE);
		beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
		registry.registerBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME, beanDefinition);
		return beanDefinition;
	}

屬性的處理

org.springframework.aop.config.AopNamespaceUtils#useClassProxyingIfNecessary

// proxy-target-calss 以及 expose-proxy屬性

private static void useClassProxyingIfNecessary(BeanDefinitionRegistry registry, @Nullable Element sourceElement) {
		if (sourceElement != null) {
		 // proxy-target-calss
			boolean proxyTargetClass = Boolean.parseBoolean(sourceElement.getAttribute(PROXY_TARGET_CLASS_ATTRIBUTE));
			if (proxyTargetClass) {
				AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
			}
			//  expose-proxy
			boolean exposeProxy = Boolean.parseBoolean(sourceElement.getAttribute(EXPOSE_PROXY_ATTRIBUTE));
			if (exposeProxy) {
				AopConfigUtils.forceAutoProxyCreatorToExposeProxy(registry);
			}
		}
	}

org.springframework.aop.config.AopConfigUtils#forceAutoProxyCreatorToUseClassProxying

public static void forceAutoProxyCreatorToUseClassProxying(BeanDefinitionRegistry registry) {
		if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {
			BeanDefinition definition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);
			definition.getPropertyValues().add("proxyTargetClass", Boolean.TRUE);
		}
	}

org.springframework.aop.config.AopConfigUtils#forceAutoProxyCreatorToExposeProxy

	public static void forceAutoProxyCreatorToExposeProxy(BeanDefinitionRegistry registry) {
		if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {
			BeanDefinition definition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);
			definition.getPropertyValues().add("exposeProxy", Boolean.TRUE);
		}
	}

總結一下：代理主要分爲以下幾種代理

CGLIB
JDK
-系統是怎麼選擇是JDK代理還是CGLIB代理呢？

JDK 針對的是interface
CGLIB 針對的是 Class.

proxy-target-class 他爲什麼出現。出現的目的是什麼？
自動適配

expose-proxy:
目標對象內部無法實現調用。
AopContext.currentProxy()獲取到當前類對象

通知

org.springframework.aop.config.AopNamespaceUtils#registerComponentIfNecessary

private static void registerComponentIfNecessary(@Nullable BeanDefinition beanDefinition, ParserContext parserContext) {
		if (beanDefinition != null) {
			parserContext.registerComponent(
					new BeanComponentDefinition(beanDefinition, AopConfigUtils.AUTO_PROXY_CREATOR_BEAN_NAME));
		}
}

org.springframework.beans.factory.xml.ParserContext#registerComponent

public void registerComponent(ComponentDefinition component) {
// 等待派發、直接觸發。
		CompositeComponentDefinition containingComponent = getContainingComponent();
		if (containingComponent != null) {
			containingComponent.addNestedComponent(component);
		}
		else {
			this.readerContext.fireComponentRegistered(component);
		}
	}

下面介紹創建Aop代理

這是spring優雅的地方，通過spring的BeanPostProcess接口xxxxx…
org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#postProcessAfterInitialization

/**
	 * Create a proxy with the configured interceptors if the bean is
	 * identified as one to proxy by the subclass.
	 * @see #getAdvicesAndAdvisorsForBean
	 */
	@Override
	public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
		if (bean != null) {
		  // 構建 key的規則  className_beanName
			Object cacheKey = getCacheKey(bean.getClass(), beanName);
			if (this.earlyProxyReferences.remove(cacheKey) != bean) {
			// 如果他合適被代理，則需要被代理指定的bean
				return wrapIfNecessary(bean, beanName, cacheKey);
			}
		}
		return bean;
	}

org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#wrapIfNecessary

/**
	 * Wrap the given bean if necessary, i.e. if it is eligible for being proxied.
	 * @param bean the raw bean instance
	 * @param beanName the name of the bean
	 * @param cacheKey the cache key for metadata access
	 * @return a proxy wrapping the bean, or the raw bean instance as-is
	 */
	protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
	// 如果已經被處理過
		if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
			return bean;
		}
		// 無需zhen
		if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
			return bean;
		}
		if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
			this.advisedBeans.put(cacheKey, Boolean.FALSE);
			return bean;
		}

		// Create proxy if we have advice.
		Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
		// 如果獲取到了增強則需要針對增強創建代理
		if (specificInterceptors != DO_NOT_PROXY) {
			this.advisedBeans.put(cacheKey, Boolean.TRUE);
			// 創建代理
			Object proxy = createProxy(
					bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
			this.proxyTypes.put(cacheKey, proxy.getClass());
			return proxy;
		}
		this.advisedBeans.put(cacheKey, Boolean.FALSE);
		return bean;
	}

通過上面的代碼我們已經感覺到aop整合spring開始啦
創建代理對象分爲一下兩個方面

獲取增強的方法或者增強器
根據獲取到增強進行代理

AbstractAutoProxyCreator

BeanNameAutoProxyCreator
AbstractAdvisorAutoProxyCreator

org.springframework.aop.framework.autoproxy.AbstractAdvisorAutoProxyCreator#getAdvicesAndAdvisorsForBean

	protected Object[] getAdvicesAndAdvisorsForBean(
			Class<?> beanClass, String beanName, @Nullable TargetSource targetSource) {
    
		List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
		if (advisors.isEmpty()) {
			return DO_NOT_PROXY;
		}
		return advisors.toArray();
	}

org.springframework.aop.framework.autoproxy.AbstractAdvisorAutoProxyCreator#findEligibleAdvisors

protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
		List<Advisor> candidateAdvisors = findCandidateAdvisors();
		List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
		extendAdvisors(eligibleAdvisors);
		if (!eligibleAdvisors.isEmpty()) {
			eligibleAdvisors = sortAdvisors(eligibleAdvisors);
		}
		return eligibleAdvisors;
	}

總結一下: 獲取所有增強以及尋找所有增強中適應於bean的增強並應用.

// next 分析 …

獲取增強器繼續分析

org.springframework.aop.aspectj.annotation.AnnotationAwareAspectJAutoProxyCreator#findCandidateAdvisors

protected List<Advisor> findCandidateAdvisors() {
		// Add all the Spring advisors found according to superclass rules.
		List<Advisor> advisors = super.findCandidateAdvisors();
		// Build Advisors for all AspectJ aspects in the bean factory.
		if (this.aspectJAdvisorsBuilder != null) {
			advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors());
		}
		return advisors;
	}

org.springframework.aop.aspectj.annotation.BeanFactoryAspectJAdvisorsBuilder#buildAspectJAdvisors


	/**
	 * Look for AspectJ-annotated aspect beans in the current bean factory,
	 * and return to a list of Spring AOP Advisors representing them.
	 * <p>Creates a Spring Advisor for each AspectJ advice method.
	 * @return the list of {@link org.springframework.aop.Advisor} beans
	 * @see #isEligibleBean
	 */
	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<>();
					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);
						if (beanType == null) {
							continue;
						}
						if (this.advisorFactory.isAspect(beanType)) {
							aspectNames.add(beanName);
							AspectMetadata amd = new AspectMetadata(beanType, beanName);
							if (amd.getAjType().getPerClause().getKind() == PerClauseKind.SINGLETON) {
								MetadataAwareAspectInstanceFactory factory =
										new BeanFactoryAspectInstanceFactory(this.beanFactory, beanName);
								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;
	}

org.springframework.aop.aspectj.annotation.ReflectiveAspectJAdvisorFactory#getAdvisors

public List<Advisor> getAdvisors(MetadataAwareAspectInstanceFactory aspectInstanceFactory) {
		//獲取標記爲AspectJ類
		Class<?> aspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
		// 獲取標記爲AspectJ的name
		String aspectName = aspectInstanceFactory.getAspectMetadata().getAspectName();
		validate(aspectClass);

		// We need to wrap the MetadataAwareAspectInstanceFactory with a decorator
		// so that it will only instantiate once.
		// 
		MetadataAwareAspectInstanceFactory lazySingletonAspectInstanceFactory =
				new LazySingletonAspectInstanceFactoryDecorator(aspectInstanceFactory);

		List<Advisor> advisors = new ArrayList<>();
		for (Method method : getAdvisorMethods(aspectClass)) {
			Advisor advisor = getAdvisor(method, lazySingletonAspectInstanceFactory, advisors.size(), aspectName);
			if (advisor != null) {
				advisors.add(advisor);
			}
		}

		// If it's a per target aspect, emit the dummy instantiating aspect.
		if (!advisors.isEmpty() && lazySingletonAspectInstanceFactory.getAspectMetadata().isLazilyInstantiated()) {
			Advisor instantiationAdvisor = new SyntheticInstantiationAdvisor(lazySingletonAspectInstanceFactory);
			advisors.add(0, instantiationAdvisor);
		}

		// Find introduction fields.
		for (Field field : aspectClass.getDeclaredFields()) {
			Advisor advisor = getDeclareParentsAdvisor(field);
			if (advisor != null) {
				advisors.add(advisor);
			}
		}

		return advisors;
	}

org.springframework.aop.aspectj.annotation.ReflectiveAspectJAdvisorFactory#getAdvisor

public Advisor getAdvisor(Method candidateAdviceMethod, MetadataAwareAspectInstanceFactory aspectInstanceFactory,
			int declarationOrderInAspect, String aspectName) {

		validate(aspectInstanceFactory.getAspectMetadata().getAspectClass());

		AspectJExpressionPointcut expressionPointcut = getPointcut(
				candidateAdviceMethod, aspectInstanceFactory.getAspectMetadata().getAspectClass());
		if (expressionPointcut == null) {
			return null;
		}
		// 根據切點信息生成增強類的信息
		return new InstantiationModelAwarePointcutAdvisorImpl(expressionPointcut, candidateAdviceMethod,
				this, aspectInstanceFactory, declarationOrderInAspect, aspectName);
	}

Spring Aop 源碼分析