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4、目标方法的调用
如果没有拦截器会对目标对象方法直接调用。对于JDKDynamicAopProxy代理对象是通过AopUtils使用反射机制实现的。在这个调用方法中首先得到调用方法的反射对象，然后使用invoke启动对方法反射对象的调用。源码如下：/** * Invoke the given target via reflection, as part of an AOP method invocation. * @param target the target object * @param method the method to invoke * @param args the arguments for the method * @return the invocation result, if any * @throws Throwable if thrown by the target method * @throws org.springframework.aop.AopInvocationException in case of a reflection error */ public static Object invokeJoinpointUsingReflection(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); } }} 5、AOP拦截器的调用
下面进入AOP的核心部分，Aop是怎样完成对目标的增强的。这些都封装在Aop拦截器链中，由一个具体的拦截器完成。 无论是使用JDKDynamicAopProxy还是使用CglibAopProxy创建代理对象最终对AOP拦截链的调用都是在ReflectiveMethodInvocation中通过proceed方法实现的。在proceed方法中逐个运行拦截器的拦截方法。在运行拦截器的拦截方法之前需要对代理方法完成一个匹配，通过这个匹配判断来决定拦截器是否满足切面增强的要求。具体代码如下：public Object proceed() throws Throwable { // We start with an index of -1 and increment early. // 从索引为-1的拦截器开始调用，并按序递增 // 如果拦截器链里的拦截器迭代调用完毕，这里开始调用target函数，这个函数是通过反射机制完成 // 具体在AopUtils.invokeJoinpointUsingReflection方法中完成 if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) { return invokeJoinpoint(); } // 这里沿着定义好的interceptorOrInterceptionAdvice链进行处理 Object interceptorOrInterceptionAdvice = this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex); // 这里对拦截器进行动态匹配判断 if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) { // Evaluate dynamic method matcher here: static part will already have // been evaluated and found to match. // 前面分析的Pointcut，这里是触发匹配的地方，如果定义的Pointcut匹配，那么这个advice将会得到执行 InterceptorAndDynamicMethodMatcher dm = (InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice; 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. // 如果不匹配，proceed会递归调用，知道所有的拦截器被运行 return proceed(); } } else { // It's an interceptor, so we just invoke it: The pointcut will have // been evaluated statically before this object was constructed. // 如果是一个拦截器，直接调用这个interceptor对应的方法 return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this); } } 这时我们会有疑问，这些advisor是怎样从配置文件中获得并配置到proxy的拦截器链中，我们使用的advisor通知时怎样起作用的，让我们带着这些问题继续往下看。
6、配置通知器 在整个AopProxy代理对象拦截回调过程中，先回到ReflectionMethodInvocation类的proceed方法，在这个方法里，可以看到得到了配置的interceptorOrInterceptionAdvice，如下所示：Object interceptorOrInterceptionAdvice = this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
interceptorOrInterceptionAdvice是获得的拦截器，他通过拦截器机制对目标对象进行增强。这个拦截器来自interceptorsAndDynamicMethodMatchers。具体来说，他是interceptorsAndDynamicMathers持有的List中的一个元素。关于如何配置拦截器的问题就转化为了List中的拦截器元素是从哪里来的，在哪里配置的问题。接着对invoke调用进行回放，回到JDKDynamicAopProxy中的invoke方法中，可以看到这个List中的interceptors是从哪个调用中获取的。对于CglibAopProxy，也有类似过程，只不过这个过程是在DynamicAdvisedInterceptor的intercept回调中实现的，如下所示：
List
从上面的代码可以看出，获取intercptors的操作是由advised对象完成的，这个advised是一个AdvisedSupport对象，从AdvisedSupport类中可以看到getInterceptorsAndDynamicInterceptionAdvice的实现。在这个方法中取得了拦截器链，再取得拦截器链的时候，为了提高拦截器链的效率，还为这个拦截器链这是了缓存。
/** * Determine a list of {@link org.aopalliance.intercept.MethodInterceptor} objects * for the given method, based on this configuration. * @param method the proxied method * @param targetClass the target class * @return List of MethodInterceptors (may also include InterceptorAndDynamicMethodMatchers) */ public List 在 DefaultAdvisorChainFactory中实现了interceptor链的获取过程，在这个过程中，首先设置了一个List，其长度是配置的通知器的个数来决定的，这个配置时在XML中对ProxyFactoryBean做的interceptNames属性的配置，然后，DefaultAdvisorChainFactory会通过一个AdvisorAdapterRegistry来实现拦截器的注册。AdvisorAdapterRegistry对advice通知的织入功能起了很大作用。有了AdvisorAdapterRegistry注册器，利用他来对ProxyFactoryBean配置中得到的通知进行适配，从而得到相应的拦截器，再把他前面设置好的List中去，完成所谓的拦截器注册过程。在拦截器适配和注册过程完成以后，List中的拦截器会被JDK生成的AopProxy代理对象的invoke方法或者CGLIB代理对象的intercept拦截方法获得，并启动拦截器的invoke方法调用，最终触发通知的切面增强。
下面看看DefaultAdvisorChainFactory是怎样生成拦截器链的：/** * A simple but definitive way of working out an advice chain for a Method, * given an {@link Advised} object. Always rebuilds each advice chain; * caching can be provided by subclasses. * * @author Juergen Hoeller * @author Rod Johnson * @author Adrian Colyer * @since 2.0.3 */@SuppressWarnings("serial")public class DefaultAdvisorChainFactory implements AdvisorChainFactory, Serializable { public List /** * Determine whether the Advisors contain matching introductions. */ // 判断Advisors是否符合要求 private static boolean hasMatchingIntroductions(Advised config, Class targetClass) { for (int i = 0; i < config.getAdvisors().length; i++) { Advisor advisor = config.getAdvisors()[i]; if (advisor instanceof IntroductionAdvisor) { IntroductionAdvisor ia = (IntroductionAdvisor) advisor; if (ia.getClassFilter().matches(targetClass)) { return true; } } } return false; } 在ProxyFactoryBean的getObject方法中对adviosr进行初始化，从XML配置中获取了advisor通知器。下面看下在ProxyFactoryBean拦截器链的初始化中获取advisor通知器
/** * Create the advisor (interceptor) chain. Aadvisors that are sourced * from a BeanFactory will be refreshed each time a new prototype instance * is added. Interceptors added programmatically through the factory API * are unaffected by such changes. */ private synchronized void initializeAdvisorChain() throws AopConfigException, BeansException { if (this.advisorChainInitialized) { return; } if (!ObjectUtils.isEmpty(this.interceptorNames)) { if (this.beanFactory == null) { throw new IllegalStateException("No BeanFactory available anymore (probably due to serialization) " + "- cannot resolve interceptor names " + Arrays.asList(this.interceptorNames)); } // Globals can't be last unless we specified a targetSource using the property... if (this.interceptorNames[this.interceptorNames.length - 1].endsWith(GLOBAL_SUFFIX) && this.targetName == null && this.targetSource == EMPTY_TARGET_SOURCE) { throw new AopConfigException("Target required after globals"); } // Materialize interceptor chain from bean names. for (String name : this.interceptorNames) { if (logger.isTraceEnabled()) { logger.trace("Configuring advisor or advice '" + name + "'"); } if (name.endsWith(GLOBAL_SUFFIX)) { if (!(this.beanFactory instanceof ListableBeanFactory)) { throw new AopConfigException( "Can only use global advisors or interceptors with a ListableBeanFactory"); } addGlobalAdvisor((ListableBeanFactory) this.beanFactory, name.substring(0, name.length() - GLOBAL_SUFFIX.length())); } else { // If we get here, we need to add a named interceptor. // We must check if it's a singleton or prototype. Object advice; if (this.singleton || this.beanFactory.isSingleton(name)) { // Add the real Advisor/Advice to the chain. // 这里是取得advisor的地方，是通过BeanFactory取得的 // 把interceptorNames这个List中interceptor名字交给 // BeanFactory，然后通过调用BeanFactory的getBean去获取 advice = this.beanFactory.getBean(name); } else { // It's a prototype Advice or Advisor: replace with a prototype. // Avoid unnecessary creation of prototype bean just for advisor chain initialization. advice = new PrototypePlaceholderAdvisor(name); } addAdvisorOnChainCreation(advice, name); } } } this.advisorChainInitialized = true; } advisor通知器的取得时委托给IOC容器完成的，但是在ProxyFactoryBean中是如何获得IOC容器，然后通过回调IOC容器的getBean方法来得到需要的通知advisor？在这里大家可以回顾下IOC容器的原理。
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