spring 源码学习笔记（三）—— spring aop

欢迎访问我的个人博客休息的风

spring aop的实现，主要通过注册InstantiationAwareBeanPostProcessor处理器，在创建bean时判断是否需要

增强。具体的注册在AbstractApplicationContext.registerBeanPostProcessors方法中将所有的

BeanPostProcessor注册到容器的beanPostProcessors中。其中对aop增强主要的

InstantiationAwareBeanPostProcessor处理器是AnnotationAwareAspectJAutoProxyCreator。整个spring aop的具体

实现大致过程为：InstantiationAwareBeanPostProcessor处理器实例化前置处理器和初始化后置处理器作为入口->

查找所有的Advisor通知器->筛选能应该于该类的Advisor通知器->根据配置选择jdk还是cglib代理->代理调用时，

通过Advisor通知器链进行拦截调用，这一过程就实现了对类的aop增强。

它的整个类图关系如下：（看不清，可在右击新标签页查看）

从上图可以看到，具体实现InstantiationAwareBeanPostProcessor是AbstractAutoProxyCreator抽象类。

这个类的实例化前置处理器和初始化后置处理器就是aop增强的入口。

public Object postProcessBeforeInstantiation(Class beanClass, String beanName) throws BeansException {
   Object cacheKey = getCacheKey(beanClass, beanName);

   if (!StringUtils.hasLength(beanName) || !this.targetSourcedBeans.contains(beanName)) {
      if (this.advisedBeans.containsKey(cacheKey)) {
         return null;
      }
      //isInfrastructureClass判断是否是aop增强处理的类
      //shouldSkip判断当前类是否为advice类
      //其实就是判断当前bean是否需要用aop定义的增加类进行增加
      if (isInfrastructureClass(beanClass) || shouldSkip(beanClass, beanName)) {
         this.advisedBeans.put(cacheKey, Boolean.FALSE);
         return null;
      }
   }

public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) throws BeansException {
   if (bean != null) {
      Object cacheKey = getCacheKey(bean.getClass(), beanName);
      if (!this.earlyProxyReferences.contains(cacheKey)) {
         //在这里进行判断是否需要织入增加，并且构造Advisor通知器
         return wrapIfNecessary(bean, beanName, cacheKey);
      }
   }
   return bean;
}

初始化后置处理器会去看是否需要包装，也就是是否需织入通知器进行增强。

protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
   if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
      return bean;
   }
   //与前置处理器呼应，advisedBeans相同的cacheKey在前置处理器时有设置为false则直接返回
   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.
   //获取与类匹配的增强通知器
   Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
   if (specificInterceptors != DO_NOT_PROXY) {
      this.advisedBeans.put(cacheKey, Boolean.TRUE);
      //开始创建代理
      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;
}

在getAdvicesAndAdvisorsForBean方法中，会去构造aop有增强作用的通知器链。

protected Object[] getAdvicesAndAdvisorsForBean(Class beanClass, String beanName, @Nullable TargetSource targetSource) {
   //发现合格的Advisor器集合
   List advisors = findEligibleAdvisors(beanClass, beanName);
   if (advisors.isEmpty()) {
      return DO_NOT_PROXY;
   }
   return advisors.toArray();
}

protected List findEligibleAdvisors(Class beanClass, String beanName) {
   //找出所有的Advisor通知器集合
   List candidateAdvisors = findCandidateAdvisors();
   //过滤出可以应用到该beanClass的Advisor通知器集合
   List eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
   //通知器扩展
   extendAdvisors(eligibleAdvisors);
   if (!eligibleAdvisors.isEmpty()) {
      //对通知器进行排序
      eligibleAdvisors = sortAdvisors(eligibleAdvisors);
   }
   //返回通知器链
   return eligibleAdvisors;
}

查找所有的通知器，委托advisorRetrievalHelper.findAdvisorBeans去完成

public List findAdvisorBeans() {
   // Determine list of advisor bean names, if not cached already.
   String[] advisorNames = null;
   synchronized (this) {
      advisorNames = this.cachedAdvisorBeanNames;
      if (advisorNames == null) {
         // Do not initialize FactoryBeans here: We need to leave all regular beans
         // uninitialized to let the auto-proxy creator apply to them!
         //获取容器中所有的Advisor类的名称
         advisorNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
               this.beanFactory, Advisor.class, true, false);
         this.cachedAdvisorBeanNames = advisorNames;
      }
   }
   //省略代码 。。。。
            try {
               //在容器里面获取通知器类，加入到通知器集合
               advisors.add(this.beanFactory.getBean(name, Advisor.class));
            }

而找出应用到该beanClass的Advisor通知器集合则是在AopUtils.findAdvisorsThatCanApply方法中实现。

public static List findAdvisorsThatCanApply(List candidateAdvisors, Class clazz) {
   if (candidateAdvisors.isEmpty()) {
      return candidateAdvisors;
   }
   List eligibleAdvisors = new LinkedList<>();
   for (Advisor candidate : candidateAdvisors) {
      //遍历通知器，处理IntroductionAdvisor类型的通知，是否可以应用到该类
      if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {
         eligibleAdvisors.add(candidate);
      }
   }
   //处理所有通知器链中不是IntroductionAdvisor类型的部分
   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;
}

判断是否可以应用到该类

public static boolean canApply(Advisor advisor, Class targetClass, boolean hasIntroductions) {
   if (advisor instanceof IntroductionAdvisor) {
      return ((IntroductionAdvisor) advisor).getClassFilter().matches(targetClass);
   }
   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;
   }
}

其中，如果是PointcutAdvisor类型的通知器，则是通过切入点的MethodMatcher判断是否匹配的。

public static boolean canApply(Pointcut pc, Class targetClass, boolean hasIntroductions) {
   Assert.notNull(pc, "Pointcut must not be null");
   if (!pc.getClassFilter().matches(targetClass)) {
      return false;
   }

   MethodMatcher methodMatcher = pc.getMethodMatcher();
   //省略一些代码。。。

   Set> classes = new LinkedHashSet<>(ClassUtils.getAllInterfacesForClassAsSet(targetClass));
   classes.add(targetClass);
   for (Class clazz : classes) {
      Method[] methods = ReflectionUtils.getAllDeclaredMethods(clazz);
      for (Method method : methods) {
         //判断目标类的方法是否与该切入点匹配
         if ((introductionAwareMethodMatcher != null &&
               introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions)) ||
               methodMatcher.matches(method, targetClass)) {
            return true;
         }
      }
   }

至此，构建合格的通知器链成功。返回这个通知器链之后，会去创建代理，返回bean的代理。

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()) {
      if (shouldProxyTargetClass(beanClass, beanName)) {
         proxyFactory.setProxyTargetClass(true);
      }
      else {
         evaluateProxyInterfaces(beanClass, proxyFactory);
      }
   }
   //构建通知器链
   Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
   proxyFactory.addAdvisors(advisors);
   proxyFactory.setTargetSource(targetSource);
   customizeProxyFactory(proxyFactory);

   proxyFactory.setFrozen(this.freezeProxy);
   if (advisorsPreFiltered()) {
      proxyFactory.setPreFiltered(true);
   }
   //通过代理工厂创建代理类
   return proxyFactory.getProxy(getProxyClassLoader());
}

在创建代理类里，有两种方式，一种是cglib,一种里jdk代理。选择哪种代理，在DefaultAopProxyFactory的

createAopProxy方法中

public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
   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.");
      }
      //使用jdk代理
      if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
         return new JdkDynamicAopProxy(config);
      }
      //使用cglib代理
      return new ObjenesisCglibAopProxy(config);
   }
   else {
      //使用jdk代理
      return new JdkDynamicAopProxy(config);
   }
}

使用cglib创建代理

public Object getProxy(@Nullable ClassLoader classLoader) {
   //省略代码。。。。
      // Configure CGLIB Enhancer...
      Enhancer enhancer = createEnhancer();
      if (classLoader != null) {
         enhancer.setClassLoader(classLoader);
         if (classLoader instanceof SmartClassLoader &&
               ((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {
            enhancer.setUseCache(false);
         }
      }
      enhancer.setSuperclass(proxySuperClass);
      enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
      enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
      enhancer.setStrategy(new ClassLoaderAwareUndeclaredThrowableStrategy(classLoader));

      //根据advised创建callbacks
      Callback[] callbacks = getCallbacks(rootClass);
      Class[] types = new Class[callbacks.length];
      for (int x = 0; x < types.length; x++) {
         types[x] = callbacks[x].getClass();
      }
      // fixedInterceptorMap only populated at this point, after getCallbacks call above
      //创建CallbackFilter，用于对目标类的每个方法选择对应的callback
      enhancer.setCallbackFilter(new ProxyCallbackFilter(
            this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset));
      enhancer.setCallbackTypes(types);

      // Generate the proxy class and create a proxy instance.
      return createProxyClassAndInstance(enhancer, callbacks);

使用cglib代理时，调用方法时的处理须调用各个对应的内部MethodInterceptor实现类的intercept方法

private static class DynamicAdvisedInterceptor implements MethodInterceptor, Serializable {

   private final AdvisedSupport advised;

   public DynamicAdvisedInterceptor(AdvisedSupport advised) {
      this.advised = advised;
   }

   @Override
   @Nullable
   public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
      //省略代码。。。。
         //构建通知器链
         List