Spring Aop源码解析（一）------ Advisor的生成

文章目录

---

aop的开启

  直接看到EnableAspectJAutoProxy注解，导入了AspectJAutoProxyRegistrar类

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(AspectJAutoProxyRegistrar.class)
public @interface EnableAspectJAutoProxy {

	/**
	 * Indicate whether subclass-based (CGLIB) proxies are to be created as opposed
	 * to standard Java interface-based proxies. The default is {@code false}.
	 */
	//默认false   采用jdk和cglib代理
	//true 只采用cglib代理
	boolean proxyTargetClass() default false;

	/**
	 * Indicate that the proxy should be exposed by the AOP framework as a {@code ThreadLocal}
	 * for retrieval via the {@link org.springframework.aop.framework.AopContext} class.
	 * Off by default, i.e. no guarantees that {@code AopContext} access will work.
	 * @since 4.3.1
	 */
	 //默认false , 不暴露代理对象(threadlocal中)
	boolean exposeProxy() default false;

}

class AspectJAutoProxyRegistrar implements ImportBeanDefinitionRegistrar {

	/**
	 * Register, escalate, and configure the AspectJ auto proxy creator based on the value
	 * of the @{@link EnableAspectJAutoProxy#proxyTargetClass()} attribute on the importing
	 * {@code @Configuration} class.
	 */
	@Override
	public void registerBeanDefinitions(
			AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
		
		//注册了AnnotationAwareAspectJAutoProxyCreator为beanDefinition到Spring容器中
		AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry);
		
		//获取主动import的类的EnableAspectJAutoProxy注解
		AnnotationAttributes enableAspectJAutoProxy =
				AnnotationConfigUtils.attributesFor(importingClassMetadata, EnableAspectJAutoProxy.class);
		//注解属性封装到beanDefinition中
		if (enableAspectJAutoProxy != null) {
			if (enableAspectJAutoProxy.getBoolean("proxyTargetClass")) {
				AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
			}
			if (enableAspectJAutoProxy.getBoolean("exposeProxy")) {
				AopConfigUtils.forceAutoProxyCreatorToExposeProxy(registry);
			}
		}
	}

}

  AnnotationAwareAspectJAutoProxyCreator继承自AbstractAutoProxyCreator，AbstractAutoProxyCreator实现了BeanPostProcessor接口。直接看到AbstractAutoProxyCreator重写的postProcessAfterInitialization方法。

public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
		if (bean != null) {
			Object cacheKey = getCacheKey(bean.getClass(), beanName);
			//循环依赖会导致提前调用wrapIfNecessary（getEarlyBeanReference方法被调用，earlyProxyReferences记录该bean），这里判断earlyProxyReferences是否存在该bean，存在则不再重复调用wrapIfNecessary
			if (this.earlyProxyReferences.remove(cacheKey) != bean) {
				//尝试生成代理对象
				return wrapIfNecessary(bean, beanName, cacheKey);
			}
		}
		return bean;
}
public Object getEarlyBeanReference(Object bean, String beanName) {
		Object cacheKey = getCacheKey(bean.getClass(), beanName);
		this.earlyProxyReferences.put(cacheKey, bean);
		return wrapIfNecessary(bean, beanName, cacheKey);
}

---

Advisor的生成

protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
		if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
			return bean;
		}
		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.
		// 寻找该bean匹配到的advisor,advisor由advice（具体的拦截逻辑）和pointCut（拦截的类或者方法）组成
		Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
		//找得到对应的advisor，生成代理对象
		if (specificInterceptors != DO_NOT_PROXY) {
			this.advisedBeans.put(cacheKey, Boolean.TRUE);
			//生成代理对象
			Object proxy = createProxy(
					bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
			this.proxyTypes.put(cacheKey, proxy.getClass());
			return proxy;
		}
		
		this.advisedBeans.put(cacheKey, Boolean.FALSE);
		//找不到，不生成代理，直接返回原本的bean
		return bean;
	}

protected Object[] getAdvicesAndAdvisorsForBean(
			Class<?> beanClass, String beanName, @Nullable TargetSource targetSource) {
		
		//寻找advisors
		List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
		if (advisors.isEmpty()) {
			return DO_NOT_PROXY;
		}
		return advisors.toArray();
}
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
		//找到实现了Advisor接口的bean,和有@Aspect注解标识的bean
		List<Advisor> candidateAdvisors = findCandidateAdvisors();
		//匹配该bean符合的advisor的
		List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
		//增加一个默认的Advisor在最前面，ExposeInvocationInterceptor.ADVISOR，
		extendAdvisors(eligibleAdvisors);
		if (!eligibleAdvisors.isEmpty()) {
			//对advisor进行排序（实现Ordered接口，Order注解，Priority注解）
			eligibleAdvisors = sortAdvisors(eligibleAdvisors);
		}
		return eligibleAdvisors;
}

protected List<Advisor> findCandidateAdvisors() {
		// Add all the Spring advisors found according to superclass rules.
		//调用父类（bstractAutoProxyCreator）的findCandidateAdvisors，找到实现了Advisor接口的bean
		List<Advisor> advisors = super.findCandidateAdvisors();
		// Build Advisors for all AspectJ aspects in the bean factory.
		//buildAspectJAdvisors()寻找@Aspect注解标识的bean
		if (this.aspectJAdvisorsBuilder != null) {
			advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors());
		}
		return advisors;
	}

protected List<Advisor> findCandidateAdvisors() {
		Assert.state(this.advisorRetrievalHelper != null, "No BeanFactoryAdvisorRetrievalHelper available");
		return this.advisorRetrievalHelper.findAdvisorBeans();
}
public List<Advisor> findAdvisorBeans() {
		// Determine list of advisor bean names, if not cached already.
		String[] advisorNames = this.cachedAdvisorBeanNames;
		//第一次进来cachedAdvisorBeanNames为空
		if (advisorNames == null) {
			// Do not initialize FactoryBeans here: We need to leave all regular beans
			// uninitialized to let the auto-proxy creator apply to them!
			//寻找实现了Advisor接口的bean的beanName
			advisorNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
					this.beanFactory, Advisor.class, true, false);
			//cachedAdvisorBeanNames有值了
			this.cachedAdvisorBeanNames = advisorNames;
		}
		if (advisorNames.length == 0) {
			return new ArrayList<>();
		}
		
		List<Advisor> advisors = new ArrayList<>();
		//循环所有的beanName
		for (String name : advisorNames) {
			if (isEligibleBean(name)) {
				if (this.beanFactory.isCurrentlyInCreation(name)) {
					if (logger.isTraceEnabled()) {
						logger.trace("Skipping currently created advisor '" + name + "'");
					}
				}
				else {
					try {
						//从beanFactory获取bean，加入advisors中
						advisors.add(this.beanFactory.getBean(name, Advisor.class));
					}
					catch (BeanCreationException ex) {
						Throwable rootCause = ex.getMostSpecificCause();
						if (rootCause instanceof BeanCurrentlyInCreationException) {
							BeanCreationException bce = (BeanCreationException) rootCause;
							String bceBeanName = bce.getBeanName();
							if (bceBeanName != null && this.beanFactory.isCurrentlyInCreation(bceBeanName)) {
								if (logger.isTraceEnabled()) {
									logger.trace("Skipping advisor '" + name +
											"' with dependency on currently created bean: " + ex.getMessage());
								}
								// Ignore: indicates a reference back to the bean we're trying to advise.
								// We want to find advisors other than the currently created bean itself.
								continue;
							}
						}
						throw ex;
					}
				}
			}
		}
		//返回实现了Advisor接口的所有bean
		return advisors;
}

public List<Advisor> buildAspectJAdvisors() {
		List<String> aspectNames = this.aspectBeanNames;
		//第一次进来aspectBeanNames为空
		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);
					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.
						//获取到bean的类型
						Class<?> beanType = this.beanFactory.getType(beanName);
						if (beanType == null) {
							continue;
						}
						//判断该bean是否有@Aspect注解
						if (this.advisorFactory.isAspect(beanType)) {
							//往aspectNames添加beanName
							aspectNames.add(beanName);
							AspectMetadata amd = new AspectMetadata(beanType, beanName);
							if (amd.getAjType().getPerClause().getKind() == PerClauseKind.SINGLETON) {
								MetadataAwareAspectInstanceFactory factory =
										new BeanFactoryAspectInstanceFactory(this.beanFactory, beanName);
								//getAdvisors解析该bean,生成advisor
								List<Advisor> classAdvisors = this.advisorFactory.getAdvisors(factory);
								if (this.beanFactory.isSingleton(beanName)) {
									//advisor放入advisorsCache
									this.advisorsCache.put(beanName, classAdvisors);
								}
								else {
									this.aspectFactoryCache.put(beanName, factory);
								}
								//advisor放入advisors
								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));
							}
						}
					}
					//aspectBeanNames有值了
					this.aspectBeanNames = aspectNames;
					//返回所有的advisor
					return advisors;
				}
			}
		}
		
		if (aspectNames.isEmpty()) {
			return Collections.emptyList();
		}
		List<Advisor> advisors = new ArrayList<>();
		//后续再调用该方法，aspectBeanNames有值了，直接从aspectFactoryCache获取所有的advisor
		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;
	}

public List<Advisor> 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<Advisor> advisors = new ArrayList<>();
		//获取类中没有被@PointCut注解修饰的方法
		for (Method method : getAdvisorMethods(aspectClass)) {
			//解析方法注解生成advisor 
			Advisor advisor = getAdvisor(method, lazySingletonAspectInstanceFactory, 0, aspectName);
			if (advisor != null) {
				advisors.add(advisor);
			}
		}

		//省略部分源码

		return advisors;
}
private List<Method> getAdvisorMethods(Class<?> aspectClass) {
		final List<Method> methods = new ArrayList<>();
		//循环处理方法
		ReflectionUtils.doWithMethods(aspectClass, method -> {
			// Exclude pointcuts
			//没有被@PointCut注解修饰的方法加入methods
			if (AnnotationUtils.getAnnotation(method, Pointcut.class) == null) {
				methods.add(method);
			}
		}, ReflectionUtils.USER_DECLARED_METHODS);
		//对方法进行排序
		//new InstanceComparator<>(Around.class, Before.class, After.class, AfterReturning.class, AfterThrowing.class)
		//InstanceComparator实现了Comparator，返回下标值进行排序
		//@Around > @Before > @After > @AfterReturning > @AfterThrowing
		if (methods.size() > 1) {
			methods.sort(METHOD_COMPARATOR);
		}
		return methods;
}
public Advisor getAdvisor(Method candidateAdviceMethod, MetadataAwareAspectInstanceFactory aspectInstanceFactory,
			int declarationOrderInAspect, String aspectName) {
		
		validate(aspectInstanceFactory.getAspectMetadata().getAspectClass());
		
		//生成pointCut
		AspectJExpressionPointcut expressionPointcut = getPointcut(
				candidateAdviceMethod, aspectInstanceFactory.getAspectMetadata().getAspectClass());
		if (expressionPointcut == null) {
			return null;
		}
		
		//生成advice
		//和pointCut组合成advisor对象返回
		//实现了InstantiationModelAwarePointcutAdvisor 接口
		return new InstantiationModelAwarePointcutAdvisorImpl(expressionPointcut, candidateAdviceMethod,
				this, aspectInstanceFactory, declarationOrderInAspect, aspectName);
}
private AspectJExpressionPointcut getPointcut(Method candidateAdviceMethod, Class<?> candidateAspectClass) {
		//查询方法上的@Around，@Before， @After，@AfterReturning, @AfterThrowing,@Pointcut
		AspectJAnnotation<?> aspectJAnnotation =
				AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
		//没有这种注解，则不处理
		if (aspectJAnnotation == null) {
			return null;
		}
		
		AspectJExpressionPointcut ajexp =
				new AspectJExpressionPointcut(candidateAspectClass, new String[0], new Class<?>[0]);
		//将注解中的表达式，设置到pointcut的expression属性中
		ajexp.setExpression(aspectJAnnotation.getPointcutExpression());
		if (this.beanFactory != null) {
			ajexp.setBeanFactory(this.beanFactory);
		}
		return ajexp;
}

public InstantiationModelAwarePointcutAdvisorImpl(AspectJExpressionPointcut declaredPointcut,
			Method aspectJAdviceMethod, AspectJAdvisorFactory aspectJAdvisorFactory,
			MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {

		//省略部分源码
		
		//设置生成的pointcut到advisor中
		this.pointcut = this.declaredPointcut;
		this.lazy = false;
		//创建advice，设置到advisor的advice中
		this.instantiatedAdvice = instantiateAdvice(this.declaredPointcut);
		
}
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);
}
public Advice getAdvice(Method candidateAdviceMethod, AspectJExpressionPointcut expressionPointcut,
			MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {
		
		//省略部分源码
		
		//判断注解类型
		switch (aspectJAnnotation.getAnnotationType()) {
			//不同的注解生成不同的advice
			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);
		}

		//省略部分源码

		return springAdvice;
}

protected List<Advisor> findAdvisorsThatCanApply(
			List<Advisor> candidateAdvisors, Class<?> beanClass, String beanName) {

		ProxyCreationContext.setCurrentProxiedBeanName(beanName);
		try {
			//匹配该bean可用的advisor
			return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
		}
		finally {
			ProxyCreationContext.setCurrentProxiedBeanName(null);
		}
	}
public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) {
		if (candidateAdvisors.isEmpty()) {
			return candidateAdvisors;
		}
		List<Advisor> eligibleAdvisors = new ArrayList<>();
		//引介处理
		for (Advisor candidate : candidateAdvisors) {
			if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {
				eligibleAdvisors.add(candidate);
			}
		}
		boolean hasIntroductions = !eligibleAdvisors.isEmpty();
		for (Advisor candidate : candidateAdvisors) {
			//已经被引介处理过了
			if (candidate instanceof IntroductionAdvisor) {
				// already processed
				continue;
			}
			//匹配该bean可用的advisor
			if (canApply(candidate, clazz, hasIntroductions)) {
				eligibleAdvisors.add(candidate);
			}
		}
		return eligibleAdvisors;
}
public static boolean canApply(Advisor advisor, Class<?> targetClass, boolean hasIntroductions) {
		if (advisor instanceof IntroductionAdvisor) {
			return ((IntroductionAdvisor) advisor).getClassFilter().matches(targetClass);
		}
		else if (advisor instanceof PointcutAdvisor) {
			PointcutAdvisor pca = (PointcutAdvisor) advisor;
			//接着看
			return canApply(pca.getPointcut(), targetClass, hasIntroductions);
		}
		else {
			// It doesn't have a pointcut so we assume it applies.
			return true;
		}
}
public static boolean canApply(Pointcut pc, Class<?> targetClass, boolean hasIntroductions) {
		Assert.notNull(pc, "Pointcut must not be null");

		//matches方法较为繁杂，匹配的表达式可以写的很复杂，这里就不深究了。

		//判断该类是否符合Pointcut的表达式
		if (!pc.getClassFilter().matches(targetClass)) {
			return false;
		}
		
		//获取Pointcut的methodMatcher,为true代表所有方法都符合
		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) {
			Method[] methods = ReflectionUtils.getAllDeclaredMethods(clazz);
			for (Method method : methods) {
				if (introductionAwareMethodMatcher != null ?
						introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions) :
						//判断该类的方法是否符合Pointcut的表达式
						methodMatcher.matches(method, targetClass)) {
					return true;
				}
			}
		}

		return false;
	}

protected void extendAdvisors(List<Advisor> candidateAdvisors) {
		AspectJProxyUtils.makeAdvisorChainAspectJCapableIfNecessary(candidateAdvisors);
}
public static boolean makeAdvisorChainAspectJCapableIfNecessary(List<Advisor> advisors) {
		// Don't add advisors to an empty list; may indicate that proxying is just not required
		if (!advisors.isEmpty()) {
			boolean foundAspectJAdvice = false;
			for (Advisor advisor : advisors) {
				// Be careful not to get the Advice without a guard, as this might eagerly
				// instantiate a non-singleton AspectJ aspect...
				if (isAspectJAdvice(advisor)) {
					foundAspectJAdvice = true;
					break;
				}
			}
			if (foundAspectJAdvice && !advisors.contains(ExposeInvocationInterceptor.ADVISOR)) {
				//生成一个默认的advisor
				advisors.add(0, ExposeInvocationInterceptor.ADVISOR);
				return true;
			}
		}
		return false;
}
private static boolean isAspectJAdvice(Advisor advisor) {
				//advisor实现InstantiationModelAwarePointcutAdvisor 接口
		return (advisor instanceof InstantiationModelAwarePointcutAdvisor ||
				//advice继承AbstractAspectJAdvice
				advisor.getAdvice() instanceof AbstractAspectJAdvice ||
				//advisor实现PointcutAdvisor 接口
				(advisor instanceof PointcutAdvisor &&
						//Pointcut继承AspectJExpressionPointcut
						((PointcutAdvisor) advisor).getPointcut() instanceof AspectJExpressionPointcut));
}

public final class ExposeInvocationInterceptor implements MethodInterceptor, PriorityOrdered, Serializable {

	/** Singleton instance of this class. */
	//advice 实现了MethodInterceptor接口
	public static final ExposeInvocationInterceptor INSTANCE = new ExposeInvocationInterceptor();

	/**
	 * Singleton advisor for this class. Use in preference to INSTANCE when using
	 * Spring AOP, as it prevents the need to create a new Advisor to wrap the instance.
	 */
	 //public DefaultPointcutAdvisor(Advice advice) {
	 //    this(Pointcut.TRUE, advice);
	 //}
	 //Pointcut.TRUE 不需要ClassFilter匹配类 不需要methodMatcher匹配方法 被代理的bean必定符合要求使用改advisor
	public static final Advisor ADVISOR = new DefaultPointcutAdvisor(INSTANCE) {
		@Override
		public String toString() {
			return ExposeInvocationInterceptor.class.getName() +".ADVISOR";
		}
	};

	private static final ThreadLocal<MethodInvocation> invocation =
			new NamedThreadLocal<>("Current AOP method invocation");


	/**
	 * Return the AOP Alliance MethodInvocation object associated with the current invocation.
	 * @return the invocation object associated with the current invocation
	 * @throws IllegalStateException if there is no AOP invocation in progress,
	 * or if the ExposeInvocationInterceptor was not added to this interceptor chain
	 */
	 //静态方法提供外部调用
	public static MethodInvocation currentInvocation() throws IllegalStateException {
		MethodInvocation mi = invocation.get();
		if (mi == null) {
			throw new IllegalStateException(
					"No MethodInvocation found: Check that an AOP invocation is in progress and that the " +
					"ExposeInvocationInterceptor is upfront in the interceptor chain. Specifically, note that " +
					"advices with order HIGHEST_PRECEDENCE will execute before ExposeInvocationInterceptor! " +
					"In addition, ExposeInvocationInterceptor and ExposeInvocationInterceptor.currentInvocation() " +
					"must be invoked from the same thread.");
		}
		return mi;
	}


	/**
	 * Ensures that only the canonical instance can be created.
	 */
	private ExposeInvocationInterceptor() {
	}

	@Override
	public Object invoke(MethodInvocation mi) throws Throwable {
		//将methodInvocation 放入 Threadlocal中
		//methodInvocation 是个啥，我们后续文章在分析
		MethodInvocation oldInvocation = invocation.get();
		invocation.set(mi);
		try {
			return mi.proceed();
		}
		finally {
			invocation.set(oldInvocation);
		}
	}

	@Override
	public int getOrder() {
		return PriorityOrdered.HIGHEST_PRECEDENCE + 1;
	}

	/**
	 * Required to support serialization. Replaces with canonical instance
	 * on deserialization, protecting Singleton pattern.
	 * <p>Alternative to overriding the {@code equals} method.
	 */
	private Object readResolve() {
		return INSTANCE;
	}

}

  到此，advisor的生成就结束了。代理对象的生成，下期再见。