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 findEligibleAdvisors(Class<?> beanClass, String beanName) {
List candidateAdvisors = findCandidateAdvisors();
List 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?
*

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.
*

Can be called repeatedly. Effect will vary if we've added
* or removed interfaces. Can add and remove interceptors.
*

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