从Spring源码探究AOP代码织入的过程

public interface BeanPostProcessor {

	/**
	 * Apply this BeanPostProcessor to the given new bean instance <i>before</i> any bean
	 * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
	 * or a custom init-method). The bean will already be populated with property values.
	 * The returned bean instance may be a wrapper around the original.
	 * <p>The default implementation returns the given {@code bean} as-is.
	 * @param bean the new bean instance
	 * @param beanName the name of the bean
	 * @return the bean instance to use, either the original or a wrapped one;
	 * if {@code null}, no subsequent BeanPostProcessors will be invoked
	 * @throws org.springframework.beans.BeansException in case of errors
	 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
	 */
	//为在Bean的初始化前提供回调入口
	@Nullable
	default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}

	/**
	 * Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean
	 * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
	 * or a custom init-method). The bean will already be populated with property values.
	 * The returned bean instance may be a wrapper around the original.
	 * <p>In case of a FactoryBean, this callback will be invoked for both the FactoryBean
	 * instance and the objects created by the FactoryBean (as of Spring 2.0). The
	 * post-processor can decide whether to apply to either the FactoryBean or created
	 * objects or both through corresponding {@code bean instanceof FactoryBean} checks.
	 * <p>This callback will also be invoked after a short-circuiting triggered by a
	 * {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
	 * in contrast to all other BeanPostProcessor callbacks.
	 * <p>The default implementation returns the given {@code bean} as-is.
	 * @param bean the new bean instance
	 * @param beanName the name of the bean
	 * @return the bean instance to use, either the original or a wrapped one;
	 * if {@code null}, no subsequent BeanPostProcessors will be invoked
	 * @throws org.springframework.beans.BeansException in case of errors
	 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
	 * @see org.springframework.beans.factory.FactoryBean
	 */
	//为在Bean的初始化之后提供回调入口
	@Nullable
	default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}

}

	//真正创建Bean的方法
	protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
			throws BeanCreationException {
			
		//创建Bean的实例对象
		//···无关代码省略
		//(在IOC中分析过)，这里只分析AOP部分
		
		Object exposedObject = bean;
		try {
			//将Bean属性进行依赖注入
			populateBean(beanName, mbd, instanceWrapper);
			//在对Bean实例对象生成和依赖注入完成以后，开始对Bean实例对象
			//进行初始化，为Bean实例对象应用BeanPostProcessor后置处理器
			exposedObject = initializeBean(beanName, exposedObject, mbd);//注意这个方法<<<<<<<<
		}
		catch (Throwable ex) {
			if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
				throw (BeanCreationException) ex;
			}
			else {
				throw new BeanCreationException(
						mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
			}
		}
		//···无关代码省略
		//(在IOC中分析过)，这里只分析AOP部分
		//为应用返回所需要的实例对象
		return exposedObject;
	}

	//初始容器创建的Bean实例对象，为其添加BeanPostProcessor后置处理器
	protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
		//JDK的安全机制验证权限
		if (System.getSecurityManager() != null) {
			//实现PrivilegedAction接口的匿名内部类
			AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
				invokeAwareMethods(beanName, bean);
				return null;
			}, getAccessControlContext());
		}
		else {
			//为Bean实例对象包装相关属性，如名称，类加载器，所属容器等信息
			invokeAwareMethods(beanName, bean);
		}

		Object wrappedBean = bean;
		//对BeanPostProcessor后置处理器的postProcessBeforeInitialization
		//回调方法的调用，为Bean实例初始化前做一些处理
		if (mbd == null || !mbd.isSynthetic()) {
			wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
		}

		//调用Bean实例对象初始化的方法，这个初始化方法是在Spring Bean定义配置
		//文件中通过init-method属性指定的
		try {
			invokeInitMethods(beanName, wrappedBean, mbd);
		}
		catch (Throwable ex) {
			throw new BeanCreationException(
					(mbd != null ? mbd.getResourceDescription() : null),
					beanName, "Invocation of init method failed", ex);
		}
		//对BeanPostProcessor后置处理器的postProcessAfterInitialization
		//回调方法的调用，为Bean实例初始化之后做一些处理
		if (mbd == null || !mbd.isSynthetic()) {
			wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
		}

		return wrappedBean;
	}
	@Override
	//调用BeanPostProcessor后置处理器实例对象初始化之后的处理方法
	public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
			throws BeansException {

		Object result = existingBean;
		//遍历容器为所创建的Bean添加的所有BeanPostProcessor后置处理器
		for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
			//调用Bean实例所有的后置处理中的初始化后处理方法，为Bean实例对象在
			//初始化之后做一些自定义的处理操作
			Object current = beanProcessor.postProcessAfterInitialization(result, beanName);
			if (current == null) {
				return result;
			}
			result = current;
		}
		return result;
	}

	@Override
	public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) throws BeansException {
		if (bean != null) {
			Object cacheKey = getCacheKey(bean.getClass(), beanName);
			if (!this.earlyProxyReferences.contains(cacheKey)) {
				return wrapIfNecessary(bean, beanName, cacheKey);//就是这个方法<<<<<<<<
			}
		}
		return bean;
	}
	protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
		if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
			return bean;
		}

		// 判断是否不应该代理这个bean
		if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
			return bean;
		}
		/*
		 * 判断是否是一些InfrastructureClass或者是否应该跳过这个bean。
		 * 所谓InfrastructureClass就是指Advice/PointCut/Advisor等接口的实现类。
		 * shouldSkip默认实现为返回false,由于是protected方法，子类可以覆盖。
		 */
		if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
			this.advisedBeans.put(cacheKey, Boolean.FALSE);
			return bean;
		}

		// 获取这个bean的advice
		// Create proxy if we have advice.
		//一会再讲，扫描所有的相关的方法（PointCut原始方法，哪些方法需要被代理）
		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(//点进这里往下继续看
					bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
			this.proxyTypes.put(cacheKey, proxy.getClass());
			return proxy;
		}

		this.advisedBeans.put(cacheKey, Boolean.FALSE);
		return bean;
	}
	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()) {
			if (shouldProxyTargetClass(beanClass, beanName)) {
				proxyFactory.setProxyTargetClass(true);
			}
			else {
				evaluateProxyInterfaces(beanClass, proxyFactory);
			}
		}

		Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
		proxyFactory.addAdvisors(advisors);
		proxyFactory.setTargetSource(targetSource);
		customizeProxyFactory(proxyFactory);

		proxyFactory.setFrozen(this.freezeProxy);
		if (advisorsPreFiltered()) {
			proxyFactory.setPreFiltered(true);
		}

		return proxyFactory.getProxy(getProxyClassLoader());
	}

public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {

	@Override
	public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
		if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {
			Class<?> targetClass = config.getTargetClass();
			if (targetClass == null) {
				throw new AopConfigException("TargetSource cannot determine target class: " +
						"Either an interface or a target is required for proxy creation.");
			}
			if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
				return new JdkDynamicAopProxy(config);
			}
			return new ObjenesisCglibAopProxy(config);
		}
		else {
			return new JdkDynamicAopProxy(config);
		}
	}

	/**
	 * Determine whether the supplied {@link AdvisedSupport} has only the
	 * {@link org.springframework.aop.SpringProxy} interface specified
	 * (or no proxy interfaces specified at all).
	 */
	private boolean hasNoUserSuppliedProxyInterfaces(AdvisedSupport config) {
		Class<?>[] ifcs = config.getProxiedInterfaces();
		return (ifcs.length == 0 || (ifcs.length == 1 && SpringProxy.class.isAssignableFrom(ifcs[0])));
	}

}

	/**
	 * 获取代理类要实现的接口,除了Advised对象中配置的,还会加上SpringProxy, Advised(opaque=false)
	 * 检查上面得到的接口中有没有定义 equals或者hashcode的接口
	 * 调用Proxy.newProxyInstance创建代理对象
	 */
	@Override
	public Object getProxy(@Nullable ClassLoader classLoader) {
		if (logger.isDebugEnabled()) {
			logger.debug("Creating JDK dynamic proxy: target source is " + this.advised.getTargetSource());
		}
		Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
		findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
		return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
	}

	@Override
	@Nullable
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
		MethodInvocation invocation;
		Object oldProxy = null;
		boolean setProxyContext = false;

		TargetSource targetSource = this.advised.targetSource;
		Object target = null;

		try {
			//eqauls()方法，具目标对象未实现此方法
			if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
				// The target does not implement the equals(Object) method itself.
				return equals(args[0]);
			}
			//hashCode()方法，具目标对象未实现此方法
			else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
				// The target does not implement the hashCode() method itself.
				return hashCode();
			}
			else if (method.getDeclaringClass() == DecoratingProxy.class) {
				// There is only getDecoratedClass() declared -> dispatch to proxy config.
				return AopProxyUtils.ultimateTargetClass(this.advised);
			}
			//Advised接口或者其父接口中定义的方法,直接反射调用,不应用通知
			else if (!this.advised.opaque && method.getDeclaringClass().isInterface() &&
					method.getDeclaringClass().isAssignableFrom(Advised.class)) {
				// Service invocations on ProxyConfig with the proxy config...
				return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
			}

			Object retVal;

			if (this.advised.exposeProxy) {
				// Make invocation available if necessary.
				oldProxy = AopContext.setCurrentProxy(proxy);
				setProxyContext = true;
			}

			// Get as late as possible to minimize the time we "own" the target,
			// in case it comes from a pool.
			//获得目标对象的类
			target = targetSource.getTarget();
			Class<?> targetClass = (target != null ? target.getClass() : null);

			// Get the interception chain for this method.
			//获取可以应用到此方法上的Interceptor列表
			List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
			//一会要跳回这里怕你们看懵了找不到地方先提醒一下<<<<<<<<<<<<<<<<<<<<<<<<<<<<
			// Check whether we have any advice. If we don't, we can fallback on direct
			// reflective invocation of the target, and avoid creating a MethodInvocation.
			//如果没有可以应用到此方法的通知(Interceptor)，此直接反射调用 method.invoke(target, args)
			if (chain.isEmpty()) {
				// We can skip creating a MethodInvocation: just invoke the target directly
				// Note that the final invoker must be an InvokerInterceptor so we know it does
				// nothing but a reflective operation on the target, and no hot swapping or fancy proxying.
				Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
				retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
			}
			else {
				// We need to create a method invocation...
				//创建MethodInvocation
				invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
				// Proceed to the joinpoint through the interceptor chain.
				retVal = invocation.proceed();
			}

			// Massage return value if necessary.
			Class<?> returnType = method.getReturnType();
			if (retVal != null && retVal == target &&
					returnType != Object.class && returnType.isInstance(proxy) &&
					!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
				// Special case: it returned "this" and the return type of the method
				// is type-compatible. Note that we can't help if the target sets
				// a reference to itself in another returned object.
				retVal = proxy;
			}
			else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) {
				throw new AopInvocationException(
						"Null return value from advice does not match primitive return type for: " + method);
			}
			return retVal;
		}
		finally {
			if (target != null && !targetSource.isStatic()) {
				// Must have come from TargetSource.
				targetSource.releaseTarget(target);
			}
			if (setProxyContext) {
				// Restore old proxy.
				AopContext.setCurrentProxy(oldProxy);
			}
		}
	}

	public List<Object> getInterceptorsAndDynamicInterceptionAdvice(Method method, @Nullable Class<?> targetClass) {
		MethodCacheKey cacheKey = new MethodCacheKey(method);
		// 从缓存中获取
		List<Object> cached = this.methodCache.get(cacheKey);
		// 缓存未命中，则进行下一步处理
		if (cached == null) {
			// 获取所有的拦截器
			cached = this.advisorChainFactory.getInterceptorsAndDynamicInterceptionAdvice(
					this, method, targetClass);
			// 存入缓存
			this.methodCache.put(cacheKey, cached);
		}
		return cached;
	}

	/**
	 * 从提供的配置实例config中获取advisor列表,遍历处理这些advisor.如果是IntroductionAdvisor,
	 * 则判断此Advisor能否应用到目标类targetClass上.如果是PointcutAdvisor,则判断
	 * 此Advisor能否应用到目标方法method上.将满足条件的Advisor通过AdvisorAdaptor转化成Interceptor列表返回.
	 */
	@Override
	public List<Object> getInterceptorsAndDynamicInterceptionAdvice(
			Advised config, Method method, @Nullable Class<?> targetClass) {

		// This is somewhat tricky... We have to process introductions first,
		// but we need to preserve order in the ultimate list.
		List<Object> interceptorList = new ArrayList<>(config.getAdvisors().length);
		Class<?> actualClass = (targetClass != null ? targetClass : method.getDeclaringClass());
		//查看是否包含IntroductionAdvisor
		boolean hasIntroductions = hasMatchingIntroductions(config, actualClass);
		//这里实际上注册一系列AdvisorAdapter,用于将Advisor转化成MethodInterceptor
		AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();

		for (Advisor advisor : config.getAdvisors()) {
			if (advisor instanceof PointcutAdvisor) {
				// Add it conditionally.
				PointcutAdvisor pointcutAdvisor = (PointcutAdvisor) advisor;
				if (config.isPreFiltered() || pointcutAdvisor.getPointcut().getClassFilter().matches(actualClass)) {
					//这个地方这两个方法的位置可以互换下
					//将Advisor转化成Interceptor
					MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
					//检查当前advisor的pointcut是否可以匹配当前方法
					MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher();
					if (MethodMatchers.matches(mm, method, actualClass, hasIntroductions)) {
						if (mm.isRuntime()) {
							// Creating a new object instance in the getInterceptors() method
							// isn't a problem as we normally cache created chains.
							for (MethodInterceptor interceptor : interceptors) {
								interceptorList.add(new InterceptorAndDynamicMethodMatcher(interceptor, mm));
							}
						}
						else {
							interceptorList.addAll(Arrays.asList(interceptors));
						}
					}
				}
			}
			else if (advisor instanceof IntroductionAdvisor) {
				IntroductionAdvisor ia = (IntroductionAdvisor) advisor;
				if (config.isPreFiltered() || ia.getClassFilter().matches(actualClass)) {
					Interceptor[] interceptors = registry.getInterceptors(advisor);
					interceptorList.addAll(Arrays.asList(interceptors));
				}
			}
			else {
				Interceptor[] interceptors = registry.getInterceptors(advisor);
				interceptorList.addAll(Arrays.asList(interceptors));
			}
		}

		return interceptorList;
	}

			if (chain.isEmpty()) {
				// We can skip creating a MethodInvocation: just invoke the target directly
				// Note that the final invoker must be an InvokerInterceptor so we know it does
				// nothing but a reflective operation on the target, and no hot swapping or fancy proxying.
				Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
				retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
			}
			else {
				// We need to create a method invocation...
				//创建MethodInvocation
				invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
				// Proceed to the joinpoint through the interceptor chain.
				retVal = invocation.proceed();
			}

	@Override
	@Nullable
	public Object proceed() throws Throwable {
		//	We start with an index of -1 and increment early.
			//如果Interceptor执行完了，则执行joinPoint
			if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
				return invokeJoinpoint();//这里就是反射调用，下面看这里
			}

			Object interceptorOrInterceptionAdvice =
					this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
			//如果要动态匹配joinPoint
			if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
				// Evaluate dynamic method matcher here: static part will already have
				// been evaluated and found to match.
				InterceptorAndDynamicMethodMatcher dm =
						(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
				//动态匹配：运行时参数是否满足匹配条件
				if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
					return dm.interceptor.invoke(this);
				}
				else {
					// Dynamic matching failed.
					// Skip this interceptor and invoke the next in the chain.
					//动态匹配失败时,略过当前Intercetpor,调用下一个Interceptor
					return proceed();
				}
		}
		else {
			// It's an interceptor, so we just invoke it: The pointcut will have
			// been evaluated statically before this object was constructed.
			//执行当前Intercetpor
			return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
		}
	}

	protected Object invokeJoinpoint() throws Throwable {
		return AopUtils.invokeJoinpointUsingReflection(this.target, this.method, this.arguments);
	}
	@Nullable
	public static Object invokeJoinpointUsingReflection(@Nullable Object target, Method method, Object[] args)
			throws Throwable {

		// Use reflection to invoke the method.
		try {
			ReflectionUtils.makeAccessible(method);
			return method.invoke(target, args);
		}
		catch (InvocationTargetException ex) {
			// Invoked method threw a checked exception.
			// We must rethrow it. The client won't see the interceptor.
			throw ex.getTargetException();
		}
		catch (IllegalArgumentException ex) {
			throw new AopInvocationException("AOP configuration seems to be invalid: tried calling method [" +
					method + "] on target [" + target + "]", ex);
		}
		catch (IllegalAccessException ex) {
			throw new AopInvocationException("Could not access method [" + method + "]", ex);
		}
	}