Spring|Spring AOP 源码解析三（代理对象的创建） SpringAOP源码解析三（代理对象

引言上期我们对AOP核心概念及接口做了粗浅的分析，这期我们主要来探讨一下代理对象的创建过程。在开始之前，先问自己几个问题

Spring是如何帮我们去选择合适的Advice的？找到了又是通过何种方式创建代理对象的？

好了，现在我们开始分析代理对象的创建过程，首先，先来看一下AspectJAwareAdvisorAutoProxyCreator.class类的继承体系

文章图片
image.png 可以看到AspectJAwareAdvisorAutoProxyCreator.class主要实现了这几个接口

Aware Bean创建时注入一些容器属性等
BeanPostProcessor IOC 扩展点
AopInfrastructureBean 标识此类是AOP系统类，不能被代理

这里我们仅需要关注BeanPostProcessor接口的实现，因为代理的创建是在BeanPostProcessor接口的postProcessAfterInitialization方法执行时创建的，postProcessAfterInitialization方法的具体实现逻辑是在抽象父类AbstractAutoProxyCreator中实现的
入口上文中提到AspectJAwareAdvisorAutoProxyCreator.class是BeanPostProcessor接口的实现，现在就让我们打开它的入口源码慢慢分析

public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { if (bean != null) { // 返回用做缓存的key键 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 (beanName != null && this.targetSourcedBeans.contains(beanName)) { return bean; } if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) { return bean; } // 判断当前的Bean是否是AOP本身的系统类，是的话则跳过，不做代理操作 if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) { this.advisedBeans.put(cacheKey, Boolean.FALSE); return bean; }// 为该Bean找到一个合适的 advisor Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null); // 返回不为空 if (specificInterceptors != DO_NOT_PROXY) { this.advisedBeans.put(cacheKey, Boolean.TRUE); // 创建代理对象 Object proxy = createProxy( bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean)); this.proxyTypes.put(cacheKey, proxy.getClass()); return proxy; }// 没有找到合适的 advisor 则直接返回原始Bean this.advisedBeans.put(cacheKey, Boolean.FALSE); return bean; }

看完wrapIfNecessary方法，这里就是创建代理对象的全过程。其实在这个方法中一共就做了两件事情:

getAdvicesAndAdvisorsForBean方法筛选合适的Advisor对象，其实就是为当前目标对象找到合适的通知(Advice)
createProxy方法根据筛选到的切面（Advisor）集合为目标对象创建代理

下面我们分别对这两件事情作分析
寻找合适的 Advisor findEligibleAdvisors方法是在父类AbstractAdvisorAutoProxyCreator中，
且直接调用了findEligibleAdvisors 方法

List advisors = findEligibleAdvisors(beanClass, beanName); if (advisors.isEmpty()) { return DO_NOT_PROXY; } return advisors.toArray(); }

protected List findEligibleAdvisors(Class beanClass, String beanName) { // 找到容器中的全部通知 List candidateAdvisors = findCandidateAdvisors(); // 筛选合适通知对象集合 List eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName); extendAdvisors(eligibleAdvisors); if (!eligibleAdvisors.isEmpty()) { eligibleAdvisors = sortAdvisors(eligibleAdvisors); } return eligibleAdvisors; }

这里也是分开做了两件事情

首先从Spring 容器中获取到全部Advisors集合
执行筛选逻辑，获取符合条件的Advisors集合

找到Spring容器中全部 Advisor
这里是调用了BeanFactoryAdvisorRetrievalHelper.class的方法去获取到Spring 容器中全部Advisor集合的，这里需要注意BeanFactoryAdvisorRetrievalHelper.class类的初始化是在setBeanFactory方法中进行的

protected List findCandidateAdvisors() { return this.advisorRetrievalHelper.findAdvisorBeans(); }

BeanFactoryAdvisorRetrievalHelper的findAdvisorBeans方法

public List findAdvisorBeans() { // Determine list of advisor bean names, if not cached already. String[] advisorNames = null; synchronized (this) { // 尝试从缓存中获取 Advisor 类型的Bean名称 advisorNames = this.cachedAdvisorBeanNames; // if (advisorNames == null) { // 从BeanFactory中获取 Advisor 类型的全部Bean名称集合，并设置缓存 advisorNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors( this.beanFactory, Advisor.class, true, false); this.cachedAdvisorBeanNames = advisorNames; } } if (advisorNames.length == 0) { return new LinkedList(); }List advisors = new LinkedList(); // 遍历 Advisor类型 BeanName 集合 for (String name : advisorNames) { // 判断是否合法，这里返回都是true if (isEligibleBean(name)) { // 判断该Bean是否正在创建中，创建中则直接跳过 if (this.beanFactory.isCurrentlyInCreation(name)) { if (logger.isDebugEnabled()) { logger.debug("Skipping currently created advisor '" + name + "'"); } } else { try { // 根据BeanName和Advisor类型从BeanFactory中获取Bean advisors.add(this.beanFactory.getBean(name, Advisor.class)); } catch (BeanCreationException ex) { Throwable rootCause = ex.getMostSpecificCause(); if (rootCause instanceof BeanCurrentlyInCreationException) { BeanCreationException bce = (BeanCreationException) rootCause; if (this.beanFactory.isCurrentlyInCreation(bce.getBeanName())) { if (logger.isDebugEnabled()) { logger.debug("Skipping advisor '" + name + "' with dependency on currently created bean: " + ex.getMessage()); } // Ignore: indicates a reference back to the bean we're trying to advise. // We want to find advisors other than the currently created bean itself. continue; } } throw ex; } } } } return advisors; }

findAdvisorBeans方法的的目的非常明确，就是找到容器中全部的Advisor

先尝试从缓存中获取Advisor集合
缓存中不存在，则执行获取逻辑
1. 获取到了所有类型为Advisor的Bean的名称
2. 根据获取到的BeanName获取Bean

为当前Bean匹配合适的 Advisor
在以上的步骤中，我们已经拿到了容器中所有的Advisor对象集合，也就是说我们已经拿到了容器中所有已配置的AOP切面。接下里的事情就是为当前的目标对象筛选出适合的Advisor集合，现在我们开始分析AbstractAdvisorAutoProxyCreator.class的findAdvisorsThatCanApply方法

protected List findAdvisorsThatCanApply( List candidateAdvisors, Class beanClass, String beanName) {ProxyCreationContext.setCurrentProxiedBeanName(beanName); try { // 调用 AopUtils.findAdvisorsThatCanApply 为当前Bean筛选合适的 Advisor return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass); } finally { ProxyCreationContext.setCurrentProxiedBeanName(null); } }

findAdvisorsThatCanApply方法里调用了工具类AOPUtils的findAdvisorsThatCanApply方法

public static List findAdvisorsThatCanApply(List candidateAdvisors, Class clazz) { if (candidateAdvisors.isEmpty()) { return candidateAdvisors; } List eligibleAdvisors = new LinkedList(); // 先找出 IntroductionAdvisor 类型的Advisor for (Advisor candidate : candidateAdvisors) { if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) { eligibleAdvisors.add(candidate); } } boolean hasIntroductions = !eligibleAdvisors.isEmpty(); // 再从余下的Advisor中继续匹配 for (Advisor candidate : candidateAdvisors) { if (candidate instanceof IntroductionAdvisor) { // already processed continue; } if (canApply(candidate, clazz, hasIntroductions)) { eligibleAdvisors.add(candidate); } } return eligibleAdvisors; }

以上代码逻辑会先筛选出IntroductionAdvisor类型的Advisor，再筛选余下的其他Advisor

public static boolean canApply(Advisor advisor, Class targetClass) { return canApply(advisor, targetClass, false); }

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; } }

public static boolean canApply(Pointcut pc, Class targetClass, boolean hasIntroductions) { Assert.notNull(pc, "Pointcut must not be null"); // 先判断类型是否匹配 if (!pc.getClassFilter().matches(targetClass)) { return false; }// 获取切点方法匹配器 MethodMatcher methodMatcher = pc.getMethodMatcher(); if (methodMatcher == MethodMatcher.TRUE) { // No need to iterate the methods if we're matching any method anyway... return true; }IntroductionAwareMethodMatcher introductionAwareMethodMatcher = null; if (methodMatcher instanceof IntroductionAwareMethodMatcher) { introductionAwareMethodMatcher = (IntroductionAwareMethodMatcher) methodMatcher; }Set> classes = new LinkedHashSet>(ClassUtils.getAllInterfacesForClassAsSet(targetClass)); classes.add(targetClass); for (Class clazz : classes) { // 获取当前目标class的所有方法 Method[] methods = ReflectionUtils.getAllDeclaredMethods(clazz); for (Method method : methods) { // 调用 methodMatcher.matches 判断当前方法是否匹配该切点 if ((introductionAwareMethodMatcher != null && introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions)) || methodMatcher.matches(method, targetClass)) { return true; } } }return false; }

canApply是用于筛选核心方法，在上期分析连接点Pointcut接口时，我们知道Pointcut持有ClassFilter和MethodMatcher对象，具体的筛选逻辑就是由它们完成的，至于在它们具体的macthes方法是是如何实现筛选的，这里我也没有进行过深入分析，感兴趣的可以在其实现类AspectJExpressionPointcut.class中继续查看
生成代理对象在上文的分析结束后，我们已经筛选出来了合适的 Advisor，Advisor持有Advice(通知)，接下来的操作就是根据我们配置的Advice为目标对象创建代理对象了

protected Object createProxy( Class beanClass, String beanName, Object[] specificInterceptors, TargetSource targetSource) {if (this.beanFactory instanceof ConfigurableListableBeanFactory) { AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass); }// 首先创建一个代理创建工厂类，之后的操作都是为此工厂配置属性 ProxyFactory proxyFactory = new ProxyFactory(); proxyFactory.copyFrom(this); // 判断配置属性proxy-target-class是否等于False if (!proxyFactory.isProxyTargetClass()) { // 判断目标 BeanDefinition是否配置preserveTargetClass 为 ture，是的话配置CGLIB动态代理 if (shouldProxyTargetClass(beanClass, beanName)) { proxyFactory.setProxyTargetClass(true); } else { // 设置目标类接口到proxyFactory，如果没有实现接口则使用CGLIB代理 evaluateProxyInterfaces(beanClass, proxyFactory); } }Advisor[] advisors = buildAdvisors(beanName, specificInterceptors); // proxyFactory 设置 advisors proxyFactory.addAdvisors(advisors); // 设置目标对象资源 proxyFactory.setTargetSource(targetSource); customizeProxyFactory(proxyFactory); proxyFactory.setFrozen(this.freezeProxy); if (advisorsPreFiltered()) { proxyFactory.setPreFiltered(true); }// 创建代理 return proxyFactory.getProxy(getProxyClassLoader());

创建代理对象前，会新建一个代理工厂创建类，并为此工厂类配置相关属性，例如proxy-target-class的配置，虽然默认配置是false会使用JDK动态代理，但如果没有实现接口，也会自动设置proxy-target-class为true使用CGLIB创建代理对象
完成ProxyFactory的配置之后，就可以通过它创建代理对象了

/** * 创建代理对象 */ public Object getProxy(ClassLoader classLoader) { return createAopProxy().getProxy(classLoader); }

【Spring|Spring AOP 源码解析三（代理对象的创建）】调用父类ProxyCreatorSupport的createAopProxy方法，获取到代理创建工厂，工厂类(DefaultAopProxyFactory)是在父类的构造方法中创建的

protected final synchronized AopProxy createAopProxy() { if (!this.active) { activate(); } // 获取代理创建工厂类（DefaultAopProxyFactory.class）创建代理对象 return getAopProxyFactory().createAopProxy(this); }

最终在DefaultAopProxyFactory工厂类createAopProxy中创建代理对象

public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException { // 这里主要是判断 proxy-target-class 属性是否为true。默认是false 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); } // 使用CGLIB动态代理 return new ObjenesisCglibAopProxy(config); } else { // 默认使用JDK动态打理 return new JdkDynamicAopProxy(config); } }

最终的代理的创建是在ObjenesisCglibAopProxy或JdkDynamicAopProxy中完成的，至于更具体的创建逻辑，因为这一系列的源码分析只是为了能够对AOP的整体逻辑有清晰的认识，所以这里就不做更详细的分析了。
尾言本篇文章分析了AOP代理创建的整个过程，纵观整篇文章，篇幅有限，其中还有很多的点没有详细展开分析，只是粗略的分析了AOP代理的创建过程，惭愧 ... 。分析有误的地方，希望大家可以指出。
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