Spring AOP原理

@EnableAspectJAutoProxy　

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(AspectJAutoProxyRegistrar.class)
public @interface EnableAspectJAutoProxy {
    boolean proxyTargetClass() default false;
    boolean exposeProxy() default false;
}

AspectJAutoProxyRegistrar　　

AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry);

　　创建Bean（AnnotationAwareAspectJAutoProxyCreator）的定义

RootBeanDefinition beanDefinition = new RootBeanDefinition(cls);
beanDefinition.setSource(source);
beanDefinition.getPropertyValues().add("order", Ordered.HIGHEST_PRECEDENCE);
beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
// AUTO_PROXY_CREATOR_BEAN_NAME=org.springframework.aop.config.internalAutoProxyCreator
registry.registerBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME, beanDefinition);
return beanDefinition;

AnnotationAwareAspectJAutoProxyCreator　

 　　实现setBeanFactory方法　　

@Override
public void setBeanFactory(BeanFactory beanFactory) {
	super.setBeanFactory(beanFactory);
	if (!(beanFactory instanceof ConfigurableListableBeanFactory)) {
		throw new IllegalArgumentException(
				"AdvisorAutoProxyCreator requires a ConfigurableListableBeanFactory: " + beanFactory);
	}
	initBeanFactory((ConfigurableListableBeanFactory) beanFactory);
}

　　重写initBeanFactory方法

@Override
protected void initBeanFactory(ConfigurableListableBeanFactory beanFactory) {
	super.initBeanFactory(beanFactory);
	if (this.aspectJAdvisorFactory == null) {
		this.aspectJAdvisorFactory = new ReflectiveAspectJAdvisorFactory(beanFactory);
	}
	this.aspectJAdvisorsBuilder =
			new BeanFactoryAspectJAdvisorsBuilderAdapter(beanFactory, this.aspectJAdvisorFactory);
}

　　流程　　

　　1）、传入配置类，创建IOC容器

AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(TxConfig.class);
		

　　2）、注册配置类调用refresh方法刷新容器

public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) {
	this();
	register(annotatedClasses);
	refresh();
}

　　3）、注册Bean的后置处理器

// Register bean processors that intercept bean creation.
// 注册拦截bean创建的bean后置处理器
registerBeanPostProcessors(beanFactory);

　　3.1）、获取IOC容器中已有的BeanPostProcessor的定义Bean

String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

　　3.2）、添加一些其他的BeanPostProcessor

beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

　　3.3）、分离实现了PriorityOrdered接口、实现了Ordered接口、普通的BeanPostProcessor，并创建对象

// Separate between BeanPostProcessors that implement PriorityOrdered,Ordered, and the rest.
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);

　　参见创建Bean实例的步骤

　　3.4）、注册BeanPostProcessor

private static void registerBeanPostProcessors(
		ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {

	for (BeanPostProcessor postProcessor : postProcessors) {
		beanFactory.addBeanPostProcessor(postProcessor);
	}
}　　

创建Bean实例的步骤　　

　　1）、ConfigurableListableBeanFactory

<T> T getBean(String name, Class<T> requiredType) throws BeansException;

　　2）、AbstractBeanFactory

@Override
public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
	return doGetBean(name, requiredType, null, false);
}

　　3）、AbstractBeanFactory的doGetBean方法获取单例对象

// Create bean instance.
if (mbd.isSingleton()) {
	sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
		@Override
		public Object getObject() throws BeansException {
			try {
				return createBean(beanName, mbd, args);
			}
			catch (BeansException ex) {
				// Explicitly remove instance from singleton cache: It might have been put there
				// eagerly by the creation process, to allow for circular reference resolution.
				// Also remove any beans that received a temporary reference to the bean.
				destroySingleton(beanName);
				throw ex;
			}
		}
	});
	bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}

　　4）、AbstractAutowireCapableBeanFactory的creatBean方法，在IOC容器中未找到Bean则创建Bean实例

// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
// 给BeanPostProcessors一个机会去创建代理对象代替Bean实例，参见
Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
if (bean != null) {
	return bean;
}
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
return beanInstance;

　　5）、AbstractAutowireCapableBeanFactory的doCreateBean方法

// 实例化Bean，创建Bean对象
if (instanceWrapper == null) {
	instanceWrapper = createBeanInstance(beanName, mbd, args);
}
// 为Bean对象的属性赋初始值
populateBean(beanName, mbd, instanceWrapper);
// 初始化Bean，可能调用类的init方法或afterPropertiesSet方法
if (exposedObject != null) {
	exposedObject = initializeBean(beanName, exposedObject, mbd);
}

　　6）、AbstractAutowireCapableBeanFactory的initializeBean方法

protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
	if (System.getSecurityManager() != null) {
		AccessController.doPrivileged(new PrivilegedAction<Object>() {
			@Override
			public Object run() {
				invokeAwareMethods(beanName, bean);
				return null;
			}
		}, getAccessControlContext());
	}
	else {
		// 如果Bean实现了xxxAware接口的话则调用setXXX方法注入相应对象
		invokeAwareMethods(beanName, bean);
	}

	Object wrappedBean = bean;
	if (mbd == null || !mbd.isSynthetic()) {
		// 执行初始化的前置操作
		wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
	}

	try {
		// 如果bean实现了InitializingBean接口则调用afterPropertiesSet方法
		invokeInitMethods(beanName, wrappedBean, mbd);
	}
	catch (Throwable ex) {
		throw new BeanCreationException(
				(mbd != null ? mbd.getResourceDescription() : null),
				beanName, "Invocation of init method failed", ex);
	}

	if (mbd == null || !mbd.isSynthetic()) {
		// 执行初始化的后置操作
		wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
	}
	return wrappedBean;
}

创建Bean实例的代理对象步骤

　　1）、AbstractAutowireCapableBeanFactory的resolveBeforeInstantiation方法

protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
	Object bean = null;
	if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
		// Make sure bean class is actually resolved at this point.
		if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
			Class<?> targetType = determineTargetType(beanName, mbd);
			if (targetType != null) {
				// 执行Bean初始化的前置操作
				bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
				if (bean != null) {
					// 执行Bean初始化的后置操作
					bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
				}
			}
		}
		mbd.beforeInstantiationResolved = (bean != null);
	}
	return bean;
}

　　2）、AbstractAutowireCapableBeanFactory的applyBeanPostProcessorsBeforeInstantiation方法

　　　　BeanPostProcessor是在创建Bean对象完成后，初始化Bean前后进行拦截

　　　　InstantiationAwareBeanPostProcessor是在创建Bean对象之前，先尝试用后置处理器返回代理对象

protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
	for (BeanPostProcessor bp : getBeanPostProcessors()) {
		if (bp instanceof InstantiationAwareBeanPostProcessor) {
			InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
			Object result = ibp.postProcessBeforeInstantiation(beanClass, beanName);
			if (result != null) {
				return result;
			}
		}
	}
	return null;
}

　　4）、AbstractAutoProxyCreator的postProcessBeforeInstantiation方法

@Override
public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
	Object cacheKey = getCacheKey(beanClass, beanName);

	if (beanName == null || !this.targetSourcedBeans.contains(beanName)) {
		if (this.advisedBeans.containsKey(cacheKey)) {
			return null;
		}
		// 判断是否需要跳过
		if (isInfrastructureClass(beanClass) || shouldSkip(beanClass, beanName)) {
			this.advisedBeans.put(cacheKey, Boolean.FALSE);
			return null;
		}
	}

	// Create proxy here if we have a custom TargetSource.
	// Suppresses unnecessary default instantiation of the target bean:
	// The TargetSource will handle target instances in a custom fashion.
	if (beanName != null) {
		// 判断是否有自定义的目标资源，有的话才创建代理对象
		TargetSource targetSource = getCustomTargetSource(beanClass, beanName);
		if (targetSource != null) {
			this.targetSourcedBeans.add(beanName);
			Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(beanClass, beanName, targetSource);
			Object proxy = createProxy(beanClass, beanName, specificInterceptors, targetSource);
			this.proxyTypes.put(cacheKey, proxy.getClass());
			return proxy;
		}
	}

	return null;
}

　　5）、AbstractAutowireCapableBeanFactory的applyBeanPostProcessorsAfterInitialization方法　　

@Override
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
		throws BeansException {

	Object result = existingBean;
	for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
		result = beanProcessor.postProcessAfterInitialization(result, beanName);
		if (result == null) {
			return result;
		}
	}
	return result;
}

　　6）、AbstractAutoProxyCreator的postProcessAfterInitialization方法

@Override
public Object postProcessAfterInitialization(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);
		}
	}
	return bean;
}

　　7）、AbstractAutoProxyCreator的wrapIfNecessary方法

protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
	if (beanName != null && this.targetSourcedBeans.contains(beanName)) {
		return bean;
	}
	if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
		return bean;
	}
	// 判断是否需要跳过，如果需要跳过返回原bean对象
	if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
		this.advisedBeans.put(cacheKey, Boolean.FALSE);
		return bean;
	}

	// Create proxy if we have advice.
	// 如果当前bean匹配横切点表达式则创建代理对象
	Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
	if (specificInterceptors != DO_NOT_PROXY) {
		this.advisedBeans.put(cacheKey, Boolean.TRUE);
		// 创建代理对象，JDK、CGLIB方式
		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;
}