7、Advice通知的实现 AopProxy代理对象生成时，其拦截器也一并生成。下面我们来分析下Aop是如何对目标对象进行增强的。在为AopProxy配置拦截器的实现中，有一个取得拦截器配置过程，这个过程由DefaultAvisorChainFactory实现的，而这个工厂类负责生成拦截器链，在它的getInterceptorsAndDynamicInterceptionA- dvice方法中，，有一个适配器的注册过程，通过配置Spring预先设计好的拦截器，Spring加入了它对Aop实现的处理。为详细了解这个过程，先从Defau- ltAdvisorChainFactory的实现开始，通过以下代码可以看到，在DefaultAdvisorChainFactory实现中，首先构造了一个GlobalAdvisorAdapterRegistry单件，然后对配置的Advisor通知器进行逐个遍历，这些通知链都是配置在interceptorNames中的，从getInterceptorsAndDynamicInterceptionAdvice传递进来的advised参数对象中，可以方便的取得配置的通知器，有了这些通知器，接着就是一个由 GlobalAdvisorAdapterRegistry来完成的拦截器的适配和注册。
/** * 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”), Serializable {public List<Object> getInterceptorsAndDynamicInterceptionAdvice(Advised config, Method method, 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<Object>(config.getAdvisors().length);boolean hasIntroductions = hasMatchingIntroductions(config, targetClass);// 得到注册器GlobalAdvisorAdapterRegistry，这是一个单件模式的实现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(targetClass)) {MethodInterceptor[] interceptors = registry.getInterceptors(advisor);MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher();if (MethodMatchers.matches(mm, method, targetClass, hasIntroductions)) {if (mm.isRuntime()) {(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(targetClass)) {Interceptor[] interceptors = registry.getInterceptors(advisor);interceptorList.addAll(Arrays.asList(interceptors));}}else {Interceptor[] interceptors = registry.getInterceptors(advisor);interceptorList.addAll(Arrays.asList(interceptors));}}return interceptorList;}
GlobalAdvisorAdapterRegistry的getInterceptors方法为AOP的实现做出了很大的贡献，这个方法封装着advice织入实现的入口，我们先从GlobalAdvisorAdapterRegistry的实现入手，他基本起一个适配器的作用，但同时也是单件模式，代码如下：
/*** Keep track of a single instance so we can return it to classes that request it.*/AdvisorAdapterRegistry instance = new DefaultAdvisorAdapterRegistry();/*** Return the singleton {@link DefaultAdvisorAdapterRegistry} instance.*/public static AdvisorAdapterRegistry getInstance() {return instance;}
到这里，我们知道在DefaultAdvisorAdapterRegistry中，设置了一系列的adapter适配器，这是这些适配器的实现，为Spring的advice提供了编织能力，下面我们看看DefaultAdvisorAdapterRegistry究竟发生了什么？adapter的作用具体分为两个： 1、调用adapter的support方法，通过这个方法来判断取得的advice属于什么类型的advice通知，从而根据不同的advice类型来注册不同的AdviceInterceptor，也就是前面我们看到的拦截器 2、这些AdviceInterceptor都是Spring AOP框架设计好的，是为实现不同的advice功能提供服务的。有了这些AdviceInterceptor，可以方便的使用由Spring提供的各种不同的advice来设计AOP应用。也就是说，正是这些AdviceInterceptor最终实现了advice通知在AopProxy对象中的织入功能。
/** * Default implementation of the {@link AdvisorAdapterRegistry} interface. * Supports {@link org.aopalliance.intercept.MethodInterceptor}, * {@link org.springframework.aop.MethodBeforeAdvice}, * {@link org.springframework.aop.AfterReturningAdvice}, * {@link org.springframework.aop.ThrowsAdvice}. * * @author Rod Johnson * @author Rob Harrop * @author Juergen Hoeller */@SuppressWarnings(“serial”), List<AdvisorAdapter> adapters = new ArrayList<AdvisorAdapter>(3);/*** Create a new DefaultAdvisorAdapterRegistry, registering well-known adapters.*/public DefaultAdvisorAdapterRegistry() {registerAdvisorAdapter(new MethodBeforeAdviceAdapter());registerAdvisorAdapter(new AfterReturningAdviceAdapter());registerAdvisorAdapter(new ThrowsAdviceAdapter());}public Advisor wrap(Object adviceObject) throws UnknownAdviceTypeException {if (adviceObject instanceof Advisor) {return (Advisor) adviceObject;}if (!(adviceObject instanceof Advice)) {throw new UnknownAdviceTypeException(adviceObject);}Advice advice = (Advice) adviceObject;if (advice instanceof MethodInterceptor) {DefaultPointcutAdvisor(advice);}for (AdvisorAdapter adapter : this.adapters) {// Check that it is supported.if (adapter.supportsAdvice(advice)) {return new DefaultPointcutAdvisor(advice);}}throw new UnknownAdviceTypeException(advice);}public MethodInterceptor[] getInterceptors(Advisor advisor) throws UnknownAdviceTypeException {List<MethodInterceptor> interceptors = new ArrayList<MethodInterceptor>(3);Advice advice = advisor.getAdvice();if (advice instanceof MethodInterceptor) {interceptors.add((MethodInterceptor) advice);}for (AdvisorAdapter adapter : this.adapters) {if (adapter.supportsAdvice(advice)) {interceptors.add(adapter.getInterceptor(advisor));}}if (interceptors.isEmpty()) {throw new UnknownAdviceTypeException(advisor.getAdvice());}return interceptors.toArray(new MethodInterceptor[interceptors.size()]);}(AdvisorAdapter adapter) {this.adapters.add(adapter);}}觉得自己做的到和不做的到，其实只在一念之间
