spring aop 原理学习

@EnableAspectJAutoProxy:

@Import(AspectJAutoProxyRegistrar.class)

实际是创建了一个以org.springframework.aop.config.internalAutoProxyCreator为beanid的实例AnnotationAwareAspectJAutoProxyCreator.class

===== AnnotationAwareAspectJAutoProxyCreator=== 关键是这是个什么东西？怎么创建的，创建后可以做什么事情

extends ProxyProcessorSupport

extends ProxyConfig implements Ordered, BeanClassLoaderAware, AopInfrastructureBean

implements SmartInstantiationAwareBeanPostProcessor, BeanFactoryAware

创建过程：

AnnotationAwareAspectJAutoProxyCreator创建的时机比一般的单例bean的创建时机早：registerBeanPostProcessors(beanFactory); 一般单实例bean创建需要到finishBeanFactoryInitialization(beanFactory);才会创建。

关于AspectJAwareAdvisorAutoProxyCreator的几点认识

1 AspectJAwareAdvisorAutoProxyCreator是BeanPostProcessor接口的实现类

2 postProcessBeforeInitialization方法与postProcessAfterInitialization方法实现在父类AbstractAutoProxyCreator中

3 postProcessBeforeInitialization方法是一个空实现

4 逻辑代码在postProcessAfterInitialization方法中

其实aop原理就是给指定的bean生成代理对象，在bean初始化前后，方法执行前后做功能的增强。具体bean代理类在什么时候创建的?其实是在bean创建的初始化化之后，即调用postProcessAfterInitialization时，会调用AspectJAwareAdvisorAutoProxyCreator的postProcessBeforeInitialization为Bean生成代理。

1代理对象实例化----判断是否为生成代理

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);

}

}

return bean;

}

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.
     //那些对象需要创建代理对象。不可能所有的对象都创建代理对象。通过这里判断。
	Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
	if (specificInterceptors != DO_NOT_PROXY) {
		this.advisedBeans.put(cacheKey, Boolean.TRUE);
		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;
}

/**
 * Find all eligible Advisors for auto-proxying this class.
 * @param beanClass the clazz to find advisors for
 * @param beanName the name of the currently proxied bean
 * @return the empty List, not {@code null},
 * if there are no pointcuts or interceptors
 * @see #findCandidateAdvisors
 * @see #sortAdvisors
 * @see #extendAdvisors
 */
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
	List<Advisor> candidateAdvisors = findCandidateAdvisors();
	List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName); //根据候选的advisors，寻找可以使用的advisors
	extendAdvisors(eligibleAdvisors);//向候选Advisor链的开头（也就是List.get(0)的位置）添加一个org.springframework.aop.support.DefaultPointcutAdvisor
	if (!eligibleAdvisors.isEmpty()) {
		eligibleAdvisors = sortAdvisors(eligibleAdvisors);
	}
	return eligibleAdvisors;
}

//围绕canApply方法进行判断

public static List findAdvisorsThatCanApply(List candidateAdvisors, Class<?> clazz) {

if (candidateAdvisors.isEmpty()) {

return candidateAdvisors;

}

List eligibleAdvisors = new LinkedList<>();

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;

}

if (canApply(candidate, clazz, hasIntroductions)) {

eligibleAdvisors.add(candidate);

}

}

return eligibleAdvisors;

}

/**
 * Can the given advisor apply at all on the given class?
 * <p>This is an important test as it can be used to optimize out a advisor for a class.
 * This version also takes into account introductions (for IntroductionAwareMethodMatchers).
 * @param advisor the advisor to check
 * @param targetClass class we're testing
 * @param hasIntroductions whether or not the advisor chain for this bean includes
 * any introductions
 * @return whether the pointcut can apply on any method
 */
public static boolean canApply(Advisor advisor, Class<?> targetClass, boolean hasIntroductions) {
	if (advisor instanceof IntroductionAdvisor) {
		return ((IntroductionAdvisor) advisor).getClassFilter().matches(targetClass);
	}

//第一个参数advisor的实际类型是AspectJPointcutAdvisor，它是PointcutAdvisor的子类，因此执行下面的的方法：

else if (advisor instanceof PointcutAdvisor) {

PointcutAdvisor pca = (PointcutAdvisor) advisor;

return canApply(pca.getPointcut(), targetClass, hasIntroductions);

}

else {

// It doesn't have a pointcut so we assume it applies.

return true;

}

}

这个方法其实就是拿当前Advisor对应的expression做了两层判断：

目标类必须满足expression的匹配规则

目标类中的方法必须满足expression的匹配规则，当然这里方法不是全部需要满足expression的匹配规则，有一个方法满足即可

如果以上两条都满足，那么容器则会判断该满足条件，需要被生成代理对象，具体方式为返回一个数组对象eligibleAdvisors，该数组对象中存储的是对应的Advisor。

代理对象实例化----为生成代理代码上下文梳理

如果判断了可以为对象创建，接下来在AbstractAutoProxyCreater的wrapIfNecessary看看如何创建代理对象：

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.
	Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
	if (specificInterceptors != DO_NOT_PROXY) {
		this.advisedBeans.put(cacheKey, Boolean.TRUE);
		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;
}

/**

* Create an AOP proxy for the given bean.

* @param beanClass the class of the bean

* @param beanName the name of the bean

* @param specificInterceptors the set of interceptors that is

* specific to this bean (may be empty, but not null)

* @param targetSource the TargetSource for the proxy,

* already pre-configured to access the bean

* @return the AOP proxy for the bean

* @see #buildAdvisors

*/

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()) {

//这里判断这个类：如果aop:config这个节点中proxy-target-class="false"或者proxy-target-class不配置，则不使用CGLIB代理。

if (shouldProxyTargetClass(beanClass, beanName)) {

proxyFactory.setProxyTargetClass(true);

}

else {

//如果满足条件会将这里目标对象实现的所有接口的class对象放到proxyFactory里面去。

evaluateProxyInterfaces(beanClass, proxyFactory);

}

}

//往proxyFactory里面设置属性

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());
}

/**
 * Create a new proxy according to the settings in this factory.
 * <p>Can be called repeatedly. Effect will vary if we've added
 * or removed interfaces. Can add and remove interceptors.
 * <p>Uses the given class loader (if necessary for proxy creation).
 * @param classLoader the class loader to create the proxy with
 * (or {@code null} for the low-level proxy facility's default)
 * @return the proxy object
 */
public Object getProxy(@Nullable ClassLoader classLoader) {

//实现代码就一行，但是却明确告诉我们做了两件事情：

//创建AopProxy接口实现类

//通过AopProxy接口的实现类的getProxy方法获取对应的代理

return createAopProxy().getProxy(classLoader);

}

分2步看:

第一步：createAopProxy

@SuppressWarnings("serial")

public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {

@Override
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {

/**

• ProxyConfig的isOptimize方法为true，这表示让Spring自己去优化而不是用户指定
  
  *ProxyConfig的isProxyTargetClass方法为true，这表示配置了proxy-target-class="true"
  
  *ProxyConfig满足hasNoUserSuppliedProxyInterfaces方法执行结果为true，这表示对象没有实现任何接口或者实现的接口是SpringProxy接口
  
  **/
  
  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);
  
  }
  
  }
  
  如果类没有实现接口或者让spring自己优化，或者用户指定了proxy-target-class="true"，这是使用GGLIB方式创建代理对象。

第二步：getProxy

后面就是创建JdkDynamicAopProxy或者是ObjenesisCglibAopProxy的区别了。

分别说一下两种代理方式：

JdkDynamicAopProxy

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 {
		if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
			// The target does not implement the equals(Object) method itself.
			return equals(args[0]);
		}
		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);
		}
		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.
		target = targetSource.getTarget();
		Class<?> targetClass = (target != null ? target.getClass() : null);

		// Get the interception chain for this method.
		List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);

		// 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.
		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...
			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);
		}
	}
}