Spring源码之创建AOP代理之增强器的获取

前言

在上一篇博文中我们说到了通过自定义配置完成了对AnnotationAwareAspectJAutoProxyCreator类型的自动注册，那么这个类究竟做了什么工作从而完成AOP的操作呢？首先我们看一下AnnotationAwareAspectJAutoProxyCreator的类图结构，如图：

AOP的源码解析操作入口

从UML类图中我们看到`AnnotationAwareAspectJAutoProxyCreator`这个类实现了`BeanPostProcessor`接口，而实现这个`BeanPostProcessor`后，当Spring加载这个Bean时会在实例化之前调用器`postProcessorAfterIntialization`方法，而我们就从这里进行分析AOP的逻辑

• 首先我们先看一下它父类AbstractAutoProxyCreator的postProcessorIntialization方法

• 看源码(具体实现在AbstractAutoProxyCreator.class)

	/**
	 * 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) {
			// 根据bean的class 和 name构建出一个key  格式：beanClassName_beanName
			Object cacheKey = getCacheKey(bean.getClass(), beanName);
			if (this.earlyProxyReferences.remove(cacheKey) != bean) {
				// 如果它适合被代理，则需要指定封装bean
				return wrapIfNecessary(bean, beanName, cacheKey);
			}
		}
		return bean;
}

在上面代码中用到了方法wrapIfNecessary，进入到该函数方法的内部：

• 看源码(具体实现在AbstractAutoProxyCreator.class)

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;
		}
		// 给定的bean类是否是一个基础设施类，基础设施类不应该被代理，或者配置了指定的bean不需要代理
		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
		// Create proxy if we have advice.
		Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
		if (specificInterceptors != DO_NOT_PROXY) {
			// 如果获取到了增强则需要针对增强进行代理
			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;
		}
		this.advisedBeans.put(cacheKey, Boolean.FALSE);
		return bean;
}

从上面的函数中我们可以大概看出代理的创建过程的一个雏形。当然真正的开始之前还需要一些个判断，比如是否已经处理过或者是 是否需要跳过的bean，而真正创建代理的代码是在`getAdvicesAndAdvisorsForBean`函数开始的。

** 创建代理需要两个步骤：**

1. 获取增强方法或增强器；
2. 根据获取的增强来进行代理。

上述两个步骤其中逻辑是十分复杂的，首先来看看获取增强方法的逻辑实现。获取增强的方法getAdvicesAndAdvisorsForBean是在AbstractAdvisorAuroProxyCreator中实现的，代码如下：

• 看源码(具体实现在AbstractAdvisorAuroProxyCreator.class)

@Override
@Nullable
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();
}

• 源码分析

主要查看上述函数体内的findEligibleAdvisor方法。进入该方法实现也在AbstractAdvisorAuroProxyCreator.class中

• 看源码(具体实现在AbstractAdvisorAutoProxyCreator.class)

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;
}

• 源码分析

通过findEligbleAdvisor的具体实现我们看到，对于指定bean的增强方法的获取包含了两个步骤：

1. 获取所有增强，
2. 寻找所有增强中 对于bean的增强并应用(也就是寻找匹配bean的增强器)。

函数中的findCandidateAdvisors和findAdvisorsThatCanApply便是做了这两件事

当然如果这个方法没有找到增强器，getAdvicesAndAdvisorsForBean就会返回一个DO_NOT_PROXY,DO_NOT_PROXY时已经定义好的null

获取增强器

从一开始我们分析的就是基于注解进行的AOP，所以对于findidateAdvisors的实现是由AnnotationAwareAspectJAutoProxyCreator类的findCandidateAdvisors方法完成的。

• 看源码(具体实现在AnnotationAwareAspectJAutoProxyCreator.class)

@Override
protected List<Advisor> findCandidateAdvisors() {
		// Add all the Spring advisors found according to superclass rules.
		// 当使用注解方式配置AOP的时候并不是对xml配置文件的支持进行了丢弃
		// 在这里调用父类加载配置文件中的AOP声明
		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;
}

• 源码解析：

首先我们先看一下AnnotationAwareAspectJAutoProxyCreator.class这个类的UML，

在上图中我们看到AnnotationAwareAspectJAutoProxyCreator间接继承了AbstractAdvisorsAutoProxyCreator，在实现获取增强方法中保留了父类的获取配置文件中定义的增强，是由List<Advisor> advisors = super.findCandidateAdvisors();实现；

此外同时还添加了获取Bean的注解增强的功能，是由this.aspectJAdvisorsBuilder.buildAspectJAdvisors()这个方法实现的

Spring获取增强器(增强方法)的解析思路大致如下：

1. 获取所有的beanName，这一步骤中所有的beanFactory中注册的Bean都会被提取出来。
2. 遍历所有的beanName，并找出使用**@Aspect注解声明的类，并进行进一步处理。
3. 对于标记Aspect注解的类进行增强器的提取。
4. 将提取结果加入缓存

接下来我们分析一下以上步骤的实现，首先

• 看this.aspectJAdvisorsBuilder.buildAspectJAdvisors()源码的实现(具体实现在BeanFactoryAspectJAdvisorsBuilder.class)

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<>();
					// 获取所有的beanName
					String[] beanNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
							this.beanFactory, Object.class, true, false);
					// 循环所有的beanName获取 获取声明AspectJ的类，找出对应的增强方法
					for (String beanName : beanNames) {
						// 不合法的bean 则略过，由子类定义规则返回true
						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.
						// 获取对应的bean Class类型
						Class<?> beanType = this.beanFactory.getType(beanName, false);
						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);
								// 解析标记AspectJ注解的增强方法
								List<Advisor> classAdvisors = this.advisorFactory.getAdvisors(factory);
								if (this.beanFactory.isSingleton(beanName)) {
									// 将增强器加入缓存 下次可以直接取
									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();
		}
		// 记录在缓存中
		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;
}

执行到此，Spring就完成了Advisor的提取，在上面的步骤中**最繁杂最重要**的就是增强**器的获取**，而这一步又交给了`getAdvisors`方法去实现的。(`this.advisorFactory.getAdvisors(factory);`)

• 首先看this.advisorFactory.isAspect(beanType)源码(具体实现在AbstractAspectJAdvisorFactory.class)

@Override
public boolean isAspect(Class<?> clazz) {
		return (hasAspectAnnotation(clazz) && !compiledByAjc(clazz));
	}
private boolean hasAspectAnnotation(Class<?> clazz) {
		return (AnnotationUtils.findAnnotation(clazz, Aspect.class) != null);
}

紧接着再查看一下findAnnotation方法：

@Nullable
public static <A extends Annotation> A findAnnotation(Class<?> clazz, @Nullable Class<A> annotationType) {
		if (annotationType == null) {
			return null;
		}
		// Shortcut: directly present on the element, with no merging needed?
		if (AnnotationFilter.PLAIN.matches(annotationType) ||
				AnnotationsScanner.hasPlainJavaAnnotationsOnly(clazz)) {
			// 判断此Class 是否存在Aspect.class注解
			A annotation = clazz.getDeclaredAnnotation(annotationType);
			if (annotation != null) {
				return annotation;
			}
			// For backwards compatibility, perform a superclass search with plain annotations
			// even if not marked as @Inherited: e.g. a findAnnotation search for @Deprecated
			Class<?> superclass = clazz.getSuperclass();
			if (superclass == null || superclass == Object.class) {
				return null;
			}
			return findAnnotation(superclass, annotationType);
		}
		// Exhaustive retrieval of merged annotations...
		return MergedAnnotations.from(clazz, SearchStrategy.TYPE_HIERARCHY, RepeatableContainers.none())
				.get(annotationType).withNonMergedAttributes()
				.synthesize(MergedAnnotation::isPresent).orElse(null);
}

这里如果bean存在Aspect.class注解，那么就可以获取此bean的增强器了，接下来我们回到BeanFactoryAspectJAdvisorsBuilder类中查看this.advisorFactory.getAdvisors(factory);方法。

• 看源码(具体实现在ReflectiveAspectJAdvisorFactory.class)

@Override
public List<Advisor> getAdvisors(MetadataAwareAspectInstanceFactory aspectInstanceFactory) {
		// 获取标记AspectJ的类
		Class<?> aspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
		// 获取标记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<>();
		// 对于aspect class的每一个带有注解的方法进行循环(除了@Pointcut注解的方法除外)，取得Advisor，并添加到集合里
		// 这里应该取到的是Advice，然后取得我们自定义的切面类中的PointCut，组合成Advisor
		for (Method method : getAdvisorMethods(aspectClass)) {
			// Prior to Spring Framework 5.2.7, advisors.size() was supplied as the declarationOrderInAspect
			// to getAdvisor(...) to represent the "current position" in the declared methods list.
			// However, since Java 7 the "current position" is not valid since the JDK no longer
			// returns declared methods in the order in which they are declared in the source code.
			// Thus, we now hard code the declarationOrderInAspect to 0 for all advice methods
			// discovered via reflection in order to support reliable advice ordering across JVM launches.
			// Specifically, a value of 0 aligns with the default value used in
			// AspectJPrecedenceComparator.getAspectDeclarationOrder(Advisor).
			// 将类中的方法封装成Advisor
			Advisor advisor = getAdvisor(method, lazySingletonAspectInstanceFactory, 0, 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;
}

普通增强器的获取

普通增强其的获取逻辑通过getAdvisor方法实现，实现步骤包括对切点的注解的获取以及根据注解信息生成增强。

首先我们看一下 getAdvisorMethods(aspectClass)这个方法，它很巧妙的使用接口定义一个匿名回调，把带有注解的Method都取出来，放到集合里。

• 看源码

private List<Method> getAdvisorMethods(Class<?> aspectClass) {
		List<Method> methods = new ArrayList<>();
		ReflectionUtils.doWithMethods(aspectClass, methods::add, adviceMethodFilter);
		if (methods.size() > 1) {
			methods.sort(adviceMethodComparator);
		}
		return methods;
}

然后在看一下函数体内的doWithMethods方法 具体实现在ReflectionUtils中

public static void doWithMethods(Class<?> clazz, MethodCallback mc, @Nullable MethodFilter mf) {
		// Keep backing up the inheritance hierarchy.
		Method[] methods = getDeclaredMethods(clazz, false);
		for (Method method : methods) {
			if (mf != null && !mf.matches(method)) {
				continue;
			}
			try {
				mc.doWith(method);
			}
			catch (IllegalAccessException ex) {
				throw new IllegalStateException("Not allowed to access method '" + method.getName() + "': " + ex);
			}
		}
		if (clazz.getSuperclass() != null && (mf != USER_DECLARED_METHODS || clazz.getSuperclass() != Object.class)) {
			doWithMethods(clazz.getSuperclass(), mc, mf);
		}
		else if (clazz.isInterface()) {
			for (Class<?> superIfc : clazz.getInterfaces()) {
				doWithMethods(superIfc, mc, mf);
			}
		}
}

然后我们在回到ReflectiveAspectJAdvisorFactory.class类中获取普通增强器的getAdvisor方法

• 看源码(具体实现在ReflectiveAspectJAdvisorFactory.class)

@Override
@Nullable
public Advisor getAdvisor(Method candidateAdviceMethod, MetadataAwareAspectInstanceFactory aspectInstanceFactory,
			int declarationOrderInAspect, String aspectName) {
		validate(aspectInstanceFactory.getAspectMetadata().getAspectClass());
		// 获取Pointcut信息 主要是获取Pointcut表达式
		// 把Method对象也传进去的目的是，比较Method对象上的注解，是不是下面的注解的其中的一个，
		// 如果不是返回null；如果是就把Pointcut内容包装返回
		AspectJExpressionPointcut expressionPointcut = getPointcut(
				candidateAdviceMethod, aspectInstanceFactory.getAspectMetadata().getAspectClass());
		if (expressionPointcut == null) {
			return null;
		}
		// 根据Pointcut信息生成增强器
		return new InstantiationModelAwarePointcutAdvisorImpl(expressionPointcut, candidateAdviceMethod,
				this, aspectInstanceFactory, declarationOrderInAspect, aspectName);
}

切点信息的获取

所谓获取切点信息就是指注解的表达式信息的获取，如@Before("test()")。

• 看源码(具体在ReflectiveAspectJAdvisorFactory.class)

@Nullable
private AspectJExpressionPointcut getPointcut(Method candidateAdviceMethod, Class<?> candidateAspectClass) {
		// 获取方法上的注解，比较Method对象上的注解是不是下面其中的一个，如果不是返回null
		// 被比较的注解：Pointcut.class, Around.class, Before.class, After.class, AfterReturning.class, AfterThrowing.class
		AspectJAnnotation<?> aspectJAnnotation =
				AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
		if (aspectJAnnotation == null) {
			return null;
		}
		// 使用AspectJExpressionPointcut实例封装获取的信息
		AspectJExpressionPointcut ajexp =
				new AspectJExpressionPointcut(candidateAspectClass, new String[0], new Class<?>[0]);
		// 提取到注解中的表达式并设置进去
		ajexp.setExpression(aspectJAnnotation.getPointcutExpression());
		if (this.beanFactory != null) {
			ajexp.setBeanFactory(this.beanFactory);
		}
		return ajexp;
}

我们再看一下上面使用到的findAspectJAnnotationOnMethod方法的实现

• 看源码(具体是现在AbstractAspectJAdvisorFactory.class)

@Nullable
protected static AspectJAnnotation<?> findAspectJAnnotationOnMethod(Method method) {
		for (Class<?> clazz : ASPECTJ_ANNOTATION_CLASSES) {
			AspectJAnnotation<?> foundAnnotation = findAnnotation(method, (Class<Annotation>) clazz);
			if (foundAnnotation != null) {
				return foundAnnotation;
			}
		}
		return null;
}

小插曲：注意一下上面的ASPECTJ_ANNOTATION_CLASSES变量，它设置了查找的注解类：

• 源码

private static final Class<?>[] ASPECTJ_ANNOTATION_CLASSES = new Class<?>[] {
			Pointcut.class, Around.class, Before.class, After.class, AfterReturning.class, AfterThrowing.class};

再次回到findAspectJAnnotationOnMethod方法的实现，里面使用了findAnnotation方法，跟踪该方法

• 看源码(具体实现在AbstractAspectAdvisorFacrory.class)

	/**
	 * 获取指定方法上的注解 并使用AspectAnnotation进行封装
	 * @param method
	 * @param toLookFor
	 * @param <A>
	 * @return
	 */
@Nullable
private static <A extends Annotation> AspectJAnnotation<A> findAnnotation(Method method, Class<A> toLookFor) {
		A result = AnnotationUtils.findAnnotation(method, toLookFor);
		if (result != null) {
			return new AspectJAnnotation<>(result);
		}
		else {
			return null;
		}
}

此方法的功能是获取指定方法上的注解并使用AspectJAnnotation封装。

根据切点信息获取增强类

所有的增强都由Advisor实现类InstantiationModelAwarePointCutAdvisorImpl进行统一封装。我们简单看一下其构造函数：

public InstantiationModelAwarePointcutAdvisorImpl(AspectJExpressionPointcut declaredPointcut,
			Method aspectJAdviceMethod, AspectJAdvisorFactory aspectJAdvisorFactory,
			MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {
		this.declaredPointcut = declaredPointcut;
		this.declaringClass = aspectJAdviceMethod.getDeclaringClass();
		this.methodName = aspectJAdviceMethod.getName();
		this.parameterTypes = aspectJAdviceMethod.getParameterTypes();
		this.aspectJAdviceMethod = aspectJAdviceMethod;
		this.aspectJAdvisorFactory = aspectJAdvisorFactory;
		this.aspectInstanceFactory = aspectInstanceFactory;
		this.declarationOrder = declarationOrder;
		this.aspectName = aspectName;
		if (aspectInstanceFactory.getAspectMetadata().isLazilyInstantiated()) {
			// Static part of the pointcut is a lazy type.
			Pointcut preInstantiationPointcut = Pointcuts.union(
					aspectInstanceFactory.getAspectMetadata().getPerClausePointcut(), this.declaredPointcut);
			// Make it dynamic: must mutate from pre-instantiation to post-instantiation state.
			// If it's not a dynamic pointcut, it may be optimized out
			// by the Spring AOP infrastructure after the first evaluation.
			this.pointcut = new PerTargetInstantiationModelPointcut(
					this.declaredPointcut, preInstantiationPointcut, aspectInstanceFactory);
			this.lazy = true;
		}
		else {
			// A singleton aspect.
			this.pointcut = this.declaredPointcut;
			this.lazy = false;
			// 初始化Advice
			this.instantiatedAdvice = instantiateAdvice(this.declaredPointcut);
		}
}

通过对上面的构造函数的分析，发现封装过程只是简单的将信息封装在类的实例中，所有的信息都是单纯的复制。在实例初始化的工程中还完成了对于增强器的初始化。因为不同的增强所体现的逻辑是不同的，比如`@Before("test()")`和`@After("test()")`标签的不同就是增强器的位置不同，所以需要不同的增强器来完成不同的逻辑，而根据注解中的信息初始化对应的增强器就是在`instantiateAdvice`函数中实现的，继续跟踪源码：

private Advice instantiateAdvice(AspectJExpressionPointcut pointcut) {
		Advice advice = this.aspectJAdvisorFactory.getAdvice(this.aspectJAdviceMethod, pointcut,
				this.aspectInstanceFactory, this.declarationOrder, this.aspectName);
		return (advice != null ? advice : EMPTY_ADVICE);
}

接下来再继续跟踪getAdvice函数的具体实现

• 看源码(具体实现在ReflectiveAspectJAdvisorFactory.class)

@Override
@Nullable
public Advice getAdvice(Method candidateAdviceMethod, AspectJExpressionPointcut expressionPointcut,
			MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {
		Class<?> candidateAspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
		validate(candidateAspectClass);
		AspectJAnnotation<?> aspectJAnnotation =
				AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
		if (aspectJAnnotation == null) {
			return null;
		}
		// If we get here, we know we have an AspectJ method.
		// Check that it's an AspectJ-annotated class
		if (!isAspect(candidateAspectClass)) {
			throw new AopConfigException("Advice must be declared inside an aspect type: " +
					"Offending method '" + candidateAdviceMethod + "' in class [" +
					candidateAspectClass.getName() + "]");
		}
		if (logger.isDebugEnabled()) {
			logger.debug("Found AspectJ method: " + candidateAdviceMethod);
		}
		AbstractAspectJAdvice springAdvice;
		// 根据不同的注解类型封装不同的增强器
		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);
		}
		// Now to configure the advice...
		springAdvice.setAspectName(aspectName);
		springAdvice.setDeclarationOrder(declarationOrder);
		String[] argNames = this.parameterNameDiscoverer.getParameterNames(candidateAdviceMethod);
		if (argNames != null) {
			springAdvice.setArgumentNamesFromStringArray(argNames);
		}
		springAdvice.calculateArgumentBindings();
		return springAdvice;
}

前置增强

从上面的函数中我们看到，Spring会根据不同的注解生成不同的增强器，具体表现在了switch (aspectJAnnotation.getAnnotationType())，根据不同的类型来生成。例如在AtBefore会对应AspectJMethodBeforeAdvice，早AspectJMethodBeforeAdvice中完成了增强逻辑，

并且这里的**AspectJMethodBeforeAdvice**最后被适配器封装成**MethodBeforeAdviceInterceptor**,

如何被封装的 这有机再在分析。

我们先看一下MethodBeforeAdviceInterceptor的代码

• 看源码

public class MethodBeforeAdviceInterceptor implements MethodInterceptor, BeforeAdvice, Serializable {
	private final MethodBeforeAdvice advice;
	/**
	 * Create a new MethodBeforeAdviceInterceptor for the given advice.
	 * @param advice the MethodBeforeAdvice to wrap
	 */
	public MethodBeforeAdviceInterceptor(MethodBeforeAdvice advice) {
		Assert.notNull(advice, "Advice must not be null");
		this.advice = advice;
	}
	@Override
	@Nullable
	public Object invoke(MethodInvocation mi) throws Throwable {
		this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis());
		return mi.proceed();
	}
}

其中上述代码的MethodBeforeAdvice代表的前置增强的AspectJMethodBeforeAdvice，根据before方法来到这个类。

• 看源码(具体实现在AspectJMethodBeforeAdvice.java)

@Override
public void before(Method method, Object[] args, @Nullable Object target) throws Throwable {
		// 直接调用增强方法
		invokeAdviceMethod(getJoinPointMatch(), null, null);
}

继续跟踪函数体内的invokeAdviceMethod方法

• 看源码(具体实现在AbstractAspectJAdvice.java)

protected Object invokeAdviceMethod(
			@Nullable JoinPointMatch jpMatch, @Nullable Object returnValue, @Nullable Throwable ex)
			throws Throwable {
		return invokeAdviceMethodWithGivenArgs(argBinding(getJoinPoint(), jpMatch, returnValue, ex));
}

接着继续根据函数体内的invokeAdviceMethodWithGivenArgs方法，

• 看源码(具体实现在AbstractAspectJAdvice.java)

protected Object invokeAdviceMethodWithGivenArgs(Object[] args) throws Throwable {
		Object[] actualArgs = args;
		if (this.aspectJAdviceMethod.getParameterCount() == 0) {
			actualArgs = null;
		}
		try {
			ReflectionUtils.makeAccessible(this.aspectJAdviceMethod);
			// 通过反射调用AspectJ注解类中的增强方法
			return this.aspectJAdviceMethod.invoke(this.aspectInstanceFactory.getAspectInstance(), actualArgs);
		}
		catch (IllegalArgumentException ex) {
			throw new AopInvocationException("Mismatch on arguments to advice method [" +
					this.aspectJAdviceMethod + "]; pointcut expression [" +
					this.pointcut.getPointcutExpression() + "]", ex);
		}
		catch (InvocationTargetException ex) {
			throw ex.getTargetException();
		}
}

invokeAdviceMethodWithGivenArgs方法中的aspectJAdviceMethod正是对前置增强的方法，在这里实现了调用。

简单总结：

前置通知的大致过程是在拦截器链中放置MethodBeforeAdviceInterceptor，而在MethodBeforeAdvivceInterceptor中又放置了AspectJMethodBeforeAdvice，并在调用invoke时首先串联调用。

后置增强

相比前置增强略有不同，后置增强没有提供中间的类，而是直接在拦截器中使用过了中间的AspectJAfterAdvice，也就是直接实现了MethodInterceptor。

• 看源码(AspectJAfterAdvice.java)

public class AspectJAfterAdvice extends AbstractAspectJAdvice
		implements MethodInterceptor, AfterAdvice, Serializable {
	public AspectJAfterAdvice(
			Method aspectJBeforeAdviceMethod, AspectJExpressionPointcut pointcut, AspectInstanceFactory aif) {
		super(aspectJBeforeAdviceMethod, pointcut, aif);
	}
	@Override
	@Nullable
	public Object invoke(MethodInvocation mi) throws Throwable {
		try {
			return mi.proceed();
		}
		finally {
			// 激活增强方法
			invokeAdviceMethod(getJoinPointMatch(), null, null);
		}
	}
	@Override
	public boolean isBeforeAdvice() {
		return false;
	}
	@Override
	public boolean isAfterAdvice() {
		return true;
	}
}

其他的几个增强器，下次具体来看

寻找匹配的增强器

前面的函数中已经完成了所有增强器的解析，也就是讲解完了关于`findCandidateAdvisors`方法；但是对于所有增强器来讲，并不一定都适用于当前的bean，还要取出适合的增强器，也就是满足我们配置的通配符的增强器，具体实现在`findAdvisorsThatCanAply`中，我们需要回到最初的**AbstractAdvisorAuroProxyCreator**类中，然后进入到findEligibleAdvisors函数内的**findAdvisorsThatCanAply**方法的实现：

• 看源码(AbstractAdvisorAuroProxyCreator.java)

protected List<Advisor> findAdvisorsThatCanApply(
			List<Advisor> candidateAdvisors, Class<?> beanClass, String beanName) {
		ProxyCreationContext.setCurrentProxiedBeanName(beanName);
		try {
			// 过滤已经得到的advisors
			return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
		}
		finally {
			ProxyCreationContext.setCurrentProxiedBeanName(null);
		}
}

继续跟踪findAdvisorsThatCanApply方法：

• 看源码(AOPUtils.java)

public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) {
		if (candidateAdvisors.isEmpty()) {
			return candidateAdvisors;
		}
		List<Advisor> eligibleAdvisors = new ArrayList<>();
		// 首先处理引介增强
		/*
		 * 引介增强是一种特殊的增强，其它的增强是方法级别的增强，即只能在方法前或方法后添加增强。
		 * 而引介增强则不是添加到方法上的增强， 而是添加到类方法级别的增强，即可以为目标类动态实现某个接口，
		 * 或者动态添加某些方法。我们通过下面的事例演示引介增强的使用
		 */
		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;
			}
			// 对于普通bean的 进行处理
			if (canApply(candidate, clazz, hasIntroductions)) {
				eligibleAdvisors.add(candidate);
			}
		}
		return eligibleAdvisors;
}

findAdvisorsThatCanApply函数的主要功能时寻找增强器中适用于当前class的增强器。引介增强与普通增强的处理是不一样的，所以分开处理。而对于真正的匹配在canApply中实现。

接着跟踪canApply方法

• 看源码(AopUtils.java)

public static boolean canApply(Pointcut pc, Class<?> targetClass, boolean hasIntroductions) {
		Assert.notNull(pc, "Pointcut must not be null");
		// 通过Pointcut的条件判断此类是否匹配
		if (!pc.getClassFilter().matches(targetClass)) {
			return false;
		}
		MethodMatcher methodMatcher = pc.getMethodMatcher();
		if (methodMatcher == MethodMatcher.TRUE) {
			// No need to iterate the methods if we're matching any method anyway...
			return true;
		}
		IntroductionAwareMethodMatcher introductionAwareMethodMatcher = null;
		if (methodMatcher instanceof IntroductionAwareMethodMatcher) {
			introductionAwareMethodMatcher = (IntroductionAwareMethodMatcher) methodMatcher;
		}
		Set<Class<?>> classes = new LinkedHashSet<>();
		if (!Proxy.isProxyClass(targetClass)) {
			classes.add(ClassUtils.getUserClass(targetClass));
		}
		classes.addAll(ClassUtils.getAllInterfacesForClassAsSet(targetClass));
		for (Class<?> clazz : classes) {
			// 反射获取类中所有的方法
			Method[] methods = ReflectionUtils.getAllDeclaredMethods(clazz);
			for (Method method : methods) {
				// 根据匹配原则判断该方法是否能匹配Pointcut中的规则，如果有一个方法匹配则返回true
				if (introductionAwareMethodMatcher != null ?
						introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions) :
						methodMatcher.matches(method, targetClass)) {
					return true;
				}
			}
		}
		return false;
}

• 源码分析

首先会判断bean是否满足切点的规则，如果能满足，则获取bean的所有方法，判断是否有方法能够匹配规则，有方法匹配规则就代表Advisor能作用于该bean，该方法就会返回true，然后findAdvisorsThatCanApply函数就会将Advisor加入到eligibleAdvisors中。

最后我们以注解的规则来看一下bean的method是怎样匹配Pointcut中的规则的

• 看源码(AnnotationMethodMatcher.java)

@Override
public boolean matches(Method method, Class<?> targetClass) {
		if (matchesMethod(method)) {
			return true;
		}
		// Proxy classes never have annotations on their redeclared methods.
		if (Proxy.isProxyClass(targetClass)) {
			return false;
		}
		// The method may be on an interface, so let's check on the target class as well.
		Method specificMethod = AopUtils.getMostSpecificMethod(method, targetClass);
		return (specificMethod != method && matchesMethod(specificMethod));
	}
	private boolean matchesMethod(Method method) {
		// 可以看出判断该Advisor是否使用于bean中的method，只需看method上是否有Advisor的注解
		return (this.checkInherited ? AnnotatedElementUtils.hasAnnotation(method, this.annotationType) :
				method.isAnnotationPresent(this.annotationType));
}

至此：在后置处理器中找到了所有匹配Bean中的增强器，