spring源码解析（AOP）

个人学习整理

参考：《spring源码深度解析》

AOP即面向切面编程，采取横向切割。

下面代码是使用AOP进行方法test的横向处理，在所有test方法前后打印一些文字。

@Aspect
public class AspectTest {
    // 所有类的test方法
    @Pointcut("execution(*.*.test(..))")
    public void test(){}
    
    @Before("test()")
    public void beforeTest(){
        System.out.println("beforeTest");
    }

    @After("test()")
    public void afterTest(){
        System.out.println("afterTest");
    }
    
    @Around("test()")
    public Object aroundTest(ProceedingJoinPoint proceedingJoinPoint){
        System.out.println("before1");
        Object o = null;
        try {
            o = proceedingJoinPoint.proceed();
        } catch (Throwable throwable) {
            throwable.printStackTrace();
        }
        System.out.println("after1");
        return o;
    }
}

使用注解需要在配置文件中增加

由前面我们了解到，自定义注解会在META-INF下的spring.handlers中存在自定义标签的解析类，找到 AopNamespaceHandler

	@Override
	public void init() {
		// In 2.0 XSD as well as in 2.1 XSD.
		registerBeanDefinitionParser("config", new ConfigBeanDefinitionParser());
            // aop标签解析
		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());
	}

找到解析标签的类，AspectJAutoProxyBeanDefinitionParser，找到对应的parse方法为解析的逻辑

	public BeanDefinition parse(Element element, ParserContext parserContext) {
		// 注册AspectJAnnotationAutoProxyCreator 
                AopNamespaceUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(parserContext, element);
                // 解析子节点
		extendBeanDefinition(element, parserContext);
		return null;
	}

	public static void registerAspectJAnnotationAutoProxyCreatorIfNecessary(
			ParserContext parserContext, Element sourceElement) {
        // 注册 AnnotationAwareAspectJAutoProxyCreator
		BeanDefinition beanDefinition = AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(
				parserContext.getRegistry(), parserContext.extractSource(sourceElement));
        // 处理proxy-target-class expose-proxy属性
		useClassProxyingIfNecessary(parserContext.getRegistry(), sourceElement);
		registerComponentIfNecessary(beanDefinition, parserContext);
	}

首先是注册 AnnotationAwareAspectJAutoProxyCreator 默认代理创建器，然后解析标签的另外两个属性

	public static BeanDefinition registerAspectJAnnotationAutoProxyCreatorIfNecessary(
			BeanDefinitionRegistry registry, @Nullable Object source) {

		return registerOrEscalateApcAsRequired(AnnotationAwareAspectJAutoProxyCreator.class, registry, source);
	}

	@Nullable
	private static BeanDefinition registerOrEscalateApcAsRequired(
			Class cls, BeanDefinitionRegistry registry, @Nullable Object source) {

		Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
        // 如果已经存在了自动代理创建器且存在的自动代理创建器与现在的不一致，那么需要根据优先级来判断到底需要使用哪个
		if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {
			BeanDefinition apcDefinition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);
			if (!cls.getName().equals(apcDefinition.getBeanClassName())) {
				int currentPriority = findPriorityForClass(apcDefinition.getBeanClassName());
				int requiredPriority = findPriorityForClass(cls);
                // 比较优先级
				if (currentPriority < requiredPriority) {
					apcDefinition.setBeanClassName(cls.getName());
				}
			}
			return null;
		}

        // 若不存在自动代理创建器，则创建根据参数创建出来一个新的并注册到beanDefinition中
		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;
	}

这段逻辑就是设置自动代理创建器，然后解析标签的另两个属性

	private static void useClassProxyingIfNecessary(BeanDefinitionRegistry registry, @Nullable Element sourceElement) {
		if (sourceElement != null) {
            //proxy-target-class
			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);
			}
		}
	}

	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);
		}
	}

	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);
		}
	}

proxy-target-class如果true的话代表使用cglib代理类，不使用默认的jdk代理。 expose-proxy如果true的话代表暴露代理类，aop无法切到内部方法调用，可以通过暴露出来的代理类进行访问，即可切到。到这里parse解析已经结束了。

在看 AnnotationAwareAspectJAutoProxyCreator 类，是默认的自动代理创建器，看下类的结构，实现了BeanPostProcessor，即在spring加载bean之前会调用 postProcessAfterInitialization 方法初始化。

	public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
		if (bean != null) {
            // 根据给定的bean的class和name构建出一个key
			Object cacheKey = getCacheKey(bean.getClass(), beanName);
            // 如果提早构建出来的代理引用中不包含该bean,进行包装代理
			if (this.earlyProxyReferences.remove(cacheKey) != bean) {
				return wrapIfNecessary(bean, beanName, cacheKey);
			}
		}
		return bean;
	}

接下来进入实现代理的主菜

protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
        // 如果已经处理过
		if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
			return bean;
		}
        // 无需增强
		if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
			return bean;
		}
        // 基础设施类无需代理，或者配置了bean不需要自动代理的
		if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
			this.advisedBeans.put(cacheKey, Boolean.FALSE);
			return bean;
		}

            //如果存在增强方法则创建代理
		// Create proxy if we have advice.
		Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
		if (specificInterceptors != DO_NOT_PROXY) {
			this.advisedBeans.put(cacheKey, Boolean.TRUE);
            //创建代理
			Object proxy = createProxy(
					bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
			this.proxyTypes.put(cacheKey, proxy.getClass());
			return proxy;
		}

        //无需创建代理
		this.advisedBeans.put(cacheKey, Boolean.FALSE);
		return bean;
	}

这段逻辑主要包含两部分，一部分是判断是否需要创建代理，如果不需要则设置一下标记，另一部分是找bean对应的增强方法，并决定是否创建代理类。

	protected Object[] getAdvicesAndAdvisorsForBean(
			Class beanClass, String beanName, @Nullable TargetSource targetSource) {

		List advisors = findEligibleAdvisors(beanClass, beanName);
		if (advisors.isEmpty()) {
			return DO_NOT_PROXY;
		}
		return advisors.toArray();
	}

	protected List findEligibleAdvisors(Class beanClass, String beanName) {
        //获取所有增强器，只第一次会真正遍历查出所有增强器，后面直接拿缓存，要不每次bean加载都要跑一遍可是太**了
		List candidateAdvisors = findCandidateAdvisors();
        // 寻找所有增强器中的适用于当前bean的
		List eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
		extendAdvisors(eligibleAdvisors);
		if (!eligibleAdvisors.isEmpty()) {
			eligibleAdvisors = sortAdvisors(eligibleAdvisors);
		}
		return eligibleAdvisors;
	}

进入查找所有增强器的逻辑

	protected List findCandidateAdvisors() {
		// Add all the Spring advisors found according to superclass rules.
        // 获取父类中查到的增强器，即从配置文件中得到的增强器
		List advisors = super.findCandidateAdvisors();
		// Build Advisors for all AspectJ aspects in the bean factory.
		if (this.aspectJAdvisorsBuilder != null) {
            // 获取注解方式的增强器
			advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors());
		}
		return advisors;
	}

public List buildAspectJAdvisors() {
		List aspectNames = this.aspectBeanNames;

		if (aspectNames == null) {
			synchronized (this) {
				aspectNames = this.aspectBeanNames;
				if (aspectNames == null) {
					List advisors = new ArrayList<>();
					aspectNames = new ArrayList<>();
                    // 获取所有bean名称
					String[] beanNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
							this.beanFactory, Object.class, true, false);
                    // 遍历所有bean
					for (String beanName : beanNames) {
                        // 不合规的bean略过，空实现返回true, 可由子类扩展
						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;
						}
                        // 如果存在Aspect注解
						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 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 advisors = new ArrayList<>();
		for (String aspectName : aspectNames) {
			List 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;
	}

这段逻辑通过遍历bean，找到有 Aspect 注解的bean,然后找到增强器并记录，获取增强器的逻辑主要advisorFactory.getAdvisors中。非单例的则是直接记录工场类。

public List getAdvisors(MetadataAwareAspectInstanceFactory aspectInstanceFactory) {
		Class aspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
		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 advisors = new ArrayList<>();
        // 遍历没有PointCut注解的方法
		for (Method method : getAdvisorMethods(aspectClass)) {
            // 根据方法找相关注解及切面表达式封装
			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.
        // 如果寻找的增强器不为空且又配置了增强延迟初始化，那么需要在首位加入同步实例化增强器
		if (!advisors.isEmpty() && lazySingletonAspectInstanceFactory.getAspectMetadata().isLazilyInstantiated()) {
			Advisor instantiationAdvisor = new SyntheticInstantiationAdvisor(lazySingletonAspectInstanceFactory);
			advisors.add(0, instantiationAdvisor);
		}

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

		return advisors;
	}

遍历所有不包含PointCut注解的方法，获取增强器

	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;
		}

		return new InstantiationModelAwarePointcutAdvisorImpl(expressionPointcut, candidateAdviceMethod,
				this, aspectInstanceFactory, declarationOrderInAspect, aspectName);
	}

	private AspectJExpressionPointcut getPointcut(Method candidateAdviceMethod, Class candidateAspectClass) {
        // 获取方法上的注解
		AspectJAnnotation aspectJAnnotation =
				AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
		if (aspectJAnnotation == null) {
			return null;
		}


		AspectJExpressionPointcut ajexp =
				new AspectJExpressionPointcut(candidateAspectClass, new String[0], new Class[0]);
        // 获取切面表达式并载入
		ajexp.setExpression(aspectJAnnotation.getPointcutExpression());
		if (this.beanFactory != null) {
			ajexp.setBeanFactory(this.beanFactory);
		}
		return ajexp;
	}

    // 遍历所有敏感注解，一一与该方法匹配，找到该方法注解
	protected static AspectJAnnotation findAspectJAnnotationOnMethod(Method method) {
        //new Class[] { Pointcut.class, Around.class, Before.class, After.class, AfterReturning.class, AfterThrowing.class};
		for (Class clazz : ASPECTJ_ANNOTATION_CLASSES) {
			AspectJAnnotation foundAnnotation = findAnnotation(method, (Class) clazz);
			if (foundAnnotation != null) {
				return foundAnnotation;
			}
		}
		return null;
	}

找到方法上的注解，并解析切面表达式出来了，最终封装成 Advisor，其中在  new InstantiationModelAwarePointcutAdvisorImpl 中，除了初始化的逻辑，还包括了根据不同注解构造不同对象

switch (aspectJAnnotation.getAnnotationType()) {
			case AtPointcut:
				if (logger.isDebugEnabled()) {
					logger.debug("Processing pointcut '" + candidateAdviceMethod.getName() + "'");
				}
				return null;
			case AtAround:
				springAdvice = new AspectJAroundAdvice(
						candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
				break;
			case AtBefore:
				springAdvice = new AspectJMethodBeforeAdvice(
						candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
				break;
			case AtAfter:
				springAdvice = new AspectJAfterAdvice(
						candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
				break;
			case AtAfterReturning:
				springAdvice = new AspectJAfterReturningAdvice(
						candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
				AfterReturning afterReturningAnnotation = (AfterReturning) aspectJAnnotation.getAnnotation();
				if (StringUtils.hasText(afterReturningAnnotation.returning())) {
					springAdvice.setReturningName(afterReturningAnnotation.returning());
				}
				break;
			case AtAfterThrowing:
				springAdvice = new AspectJAfterThrowingAdvice(
						candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
				AfterThrowing afterThrowingAnnotation = (AfterThrowing) aspectJAnnotation.getAnnotation();
				if (StringUtils.hasText(afterThrowingAnnotation.throwing())) {
					springAdvice.setThrowingName(afterThrowingAnnotation.throwing());
				}
				break;
			default:
				throw new UnsupportedOperationException(
						"Unsupported advice type on method: " + candidateAdviceMethod);
		}

看到前置注解对应 AspectJMethodBeforeAdvice ，该类实现了 MethodBeforeAdvice接口，会在 MethodBeforeAdviceInterceptor 中以拦截链的形式进行调用，即达到前置增强的目的。而在后置增强器中没有提供中间类，直接实现 MethodInterceptor 包含在拦截链中。此时，获取所有增强器的逻辑完成，继续获取该bean匹配的增强器的逻辑.

	protected List findAdvisorsThatCanApply(
			List candidateAdvisors, Class beanClass, String beanName) {

		ProxyCreationContext.setCurrentProxiedBeanName(beanName);
		try {
            // 过滤得到匹配的增强器
			return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
		}
		finally {
			ProxyCreationContext.setCurrentProxiedBeanName(null);
		}
	}

public static List findAdvisorsThatCanApply(List candidateAdvisors, Class clazz) {
		if (candidateAdvisors.isEmpty()) {
			return candidateAdvisors;
		}
		List eligibleAdvisors = new ArrayList<>();
        // 首先处理引介增强
		for (Advisor candidate : candidateAdvisors) {
			if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {
				eligibleAdvisors.add(candidate);
			}
		}
		boolean hasIntroductions = !eligibleAdvisors.isEmpty();
		for (Advisor candidate : candidateAdvisors) {
			if (candidate instanceof IntroductionAdvisor) {
				// already processed
				continue;
			}
            // 处理普通bean
			if (canApply(candidate, clazz, hasIntroductions)) {
				eligibleAdvisors.add(candidate);
			}
		}
		return eligibleAdvisors;
	}

找到匹配该bean的增强器，开始创建代理

protected Object createProxy(Class beanClass, @Nullable String beanName,
			@Nullable Object[] specificInterceptors, TargetSource targetSource) {

		if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
			AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
		}

		ProxyFactory proxyFactory = new ProxyFactory();
		proxyFactory.copyFrom(this);

		if (!proxyFactory.isProxyTargetClass()) {
            // 判断是否应该代理目标类
			if (shouldProxyTargetClass(beanClass, beanName)) {
				proxyFactory.setProxyTargetClass(true);
			}
			else {
				evaluateProxyInterfaces(beanClass, proxyFactory);
			}
		}

        // 构建增强器
		Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
		proxyFactory.addAdvisors(advisors);
		proxyFactory.setTargetSource(targetSource);
		customizeProxyFactory(proxyFactory);

		proxyFactory.setFrozen(this.freezeProxy);
		if (advisorsPreFiltered()) {
			proxyFactory.setPreFiltered(true);
		}
        // 获取代理
		return proxyFactory.getProxy(getProxyClassLoader());
	}

protected Advisor[] buildAdvisors(@Nullable String beanName, @Nullable Object[] specificInterceptors) {
		// Handle prototypes correctly...
        // 解析注册的所有的interceptorName
		Advisor[] commonInterceptors = resolveInterceptorNames();

		List