@EnableAspectJAutoProxy
@EnableAspectJAutoProxy注解用于开启AOP功能，那么这个注解底层到底做了什么呢？
查看@EnableAspectJAutoProxy的源码，发现它使用@Import注解向Spring容器中注入了一个类型为AspectJAutoProxyRegistrar的Bean：
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class AspectJAutoProxyRegistrar implements ImportBeanDefinitionRegistrar { @Override public void registerBeanDefinitions( AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { // 注入一个bean名字为org.springframework.aop.config.internalAutoProxyCreator的AspectJAwareAdvisorAutoProxyCreator AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry); AnnotationAttributes enableAspectJAutoProxy = AnnotationConfigUtils.attributesFor(importingClassMetadata, EnableAspectJAutoProxy.class); if (enableAspectJAutoProxy != null) { if (enableAspectJAutoProxy.getBoolean("proxyTargetClass")) { // proxyTargetClass为true AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry); } if (enableAspectJAutoProxy.getBoolean("exposeProxy")) { // exposeProxy为true AopConfigUtils.forceAutoProxyCreatorToExposeProxy(registry); } } }} |
AspectJAutoProxyRegistrar实现了ImportBeanDefinitionRegistrar接口，而ImportBeanDefinitionRegistrar是spring提供的扩展点之一，主要用来向容器中注入BeanDefinition，spring会根据BeanDefinion来生成Bean。
那么AspectJAutoProxyRegistrar到底向容器中注入了什么BeanDefinion呢？
org.springframework.aop.config.AopConfigUtils#registerAspectJAnnotationAutoProxyCreatorIfNecessary(org.springframework.beans.factory.support.BeanDefinitionRegistry)
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@Nullablepublic static BeanDefinition registerAspectJAnnotationAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry) { return registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry, null);}@Nullablepublic static BeanDefinition registerAspectJAnnotationAutoProxyCreatorIfNecessary( BeanDefinitionRegistry registry, @Nullable Object source) { // AnnotationAwareAspectJAutoProxyCreator return registerOrEscalateApcAsRequired(AnnotationAwareAspectJAutoProxyCreator.class, registry, source);}@Nullableprivate static BeanDefinition registerOrEscalateApcAsRequired( Class<?> cls, BeanDefinitionRegistry registry, @Nullable Object source) { Assert.notNull(registry, "BeanDefinitionRegistry must not be null"); if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) { BeanDefinition apcDefinition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME); if (!cls.getName().equals(apcDefinition.getBeanClassName())) { int currentPriority = findPriorityForClass(apcDefinition.getBeanClassName()); int requiredPriority = findPriorityForClass(cls); if (currentPriority < requiredPriority) { apcDefinition.setBeanClassName(cls.getName()); } } return null; } // 注入AspectJAwareAdvisorAutoProxyCreator RootBeanDefinition beanDefinition = new RootBeanDefinition(cls); beanDefinition.setSource(source); beanDefinition.getPropertyValues().add("order", Ordered.HIGHEST_PRECEDENCE); beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE); registry.registerBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME, beanDefinition); return beanDefinition;} |
从源码可以发现AspectJAutoProxyRegistrar向容器中注入了一个类型为AnnotationAwareAspectJAutoProxyCreator的Bean。
那么AnnotationAwareAspectJAutoProxyCreator又是干什么的呢？
AnnotationAwareAspectJAutoProxyCreator主要实现了三个接口（由父类AbstractAutoProxyCreator实现）：
- 实现了BeanFactoryAware，内部持有BeanFactory的引用。
- 实现了SmartInstantiationAwareBeanPostProcessor(InstantiationAwareBeanPostProcessor).postProcessBeforeInstantiation，这个方法在bean的实例化（bean创建之前）之前执行。
- 实现了BeanPostProcessor.postProcessBeforeInitialization()，这个方法在bean的初始化之前（bean创建之后，属性被赋值之前）执行，BeanPostProcessor.postProcessAfterInitialization()在bean的初始化之后执行。
AnnotationAwareAspectJAutoProxyCreator的继承结构：
找切面
org.springframework.aop.framework.autoproxy.AbstractAdvisorAutoProxyCreator#findEligibleAdvisors
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protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) { /** * @see AnnotationAwareAspectJAutoProxyCreator#findCandidateAdvisors() */ // 获取容器中所有的切面Advisor // 这里返回的切面中的方法已经是有序的了，先按注解顺序（Around.class, Before.class, After.class, AfterReturning.class, AfterThrowing.class），再按方法名称 List<Advisor> candidateAdvisors = findCandidateAdvisors(); // 获取所有能够作用于当前Bean上的Advisor List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName); /** * @see AspectJAwareAdvisorAutoProxyCreator#extendAdvisors(java.util.List) */ // 往集合第一个位置加入了一个DefaultPointcutAdvisor extendAdvisors(eligibleAdvisors); if (!eligibleAdvisors.isEmpty()) { /** * @see AspectJAwareAdvisorAutoProxyCreator#sortAdvisors(java.util.List) */ // 这里是对切面进行排序，例如有@Order注解或者实现了Ordered接口 eligibleAdvisors = sortAdvisors(eligibleAdvisors); } return eligibleAdvisors;} |
org.springframework.aop.aspectj.annotation.AnnotationAwareAspectJAutoProxyCreator#findCandidateAdvisors
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protected List<Advisor> findCandidateAdvisors() { // Add all the Spring advisors found according to superclass rules. // 获取容器中所有的切面Advisor List<Advisor> advisors = super.findCandidateAdvisors(); // Build Advisors for all AspectJ aspects in the bean factory. if (this.aspectJAdvisorsBuilder != null) { // 这里还需要解析@Aspect注解，生成Advisor advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors()); } return advisors;} |
org.springframework.aop.support.AopUtils#findAdvisorsThatCanApply
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public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) { if (candidateAdvisors.isEmpty()) { return candidateAdvisors; } List<Advisor> eligibleAdvisors = new ArrayList<>(); // InstantiationModelAwarePointcutAdvisorImpl for (Advisor candidate : candidateAdvisors) { if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) { // IntroductionAdvisor类型为引入切面，具体类型为DeclareParentsAdvisor eligibleAdvisors.add(candidate); } } boolean hasIntroductions = !eligibleAdvisors.isEmpty(); for (Advisor candidate : candidateAdvisors) { if (candidate instanceof IntroductionAdvisor) { // already processed continue; } // PointCut中的ClassFilter.match 匹配类 // PointCut中的MethodMatcher.match 匹配方法 if (canApply(candidate, clazz, hasIntroductions)) { // @Aspect，类型为InstantiationModelAwarePointcutAdvisorImpl eligibleAdvisors.add(candidate); } } return eligibleAdvisors;} |
代理对象的创建
代理对象的创建时机位于bean的初始化之后，因为代理对象内部还是需要去调用目标对象的方法，所以需要让目标对象实例化并完成初始化后才会创建代理对象。
org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#postProcessAfterInitialization
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public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) { if (bean != null) { // 先从缓存中获取代理对象 Object cacheKey = getCacheKey(bean.getClass(), beanName); if (this.earlyProxyReferences.remove(cacheKey) != bean) { // 按需生成代理对象 return wrapIfNecessary(bean, beanName, cacheKey); } } return bean;} |
org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#wrapIfNecessary
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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. /** * @see AbstractAdvisorAutoProxyCreator#getAdvicesAndAdvisorsForBean(java.lang.Class, java.lang.String, org.springframework.aop.TargetSource) */ // 获取与当前Bean匹配的切面 Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null); if (specificInterceptors != DO_NOT_PROXY) { this.advisedBeans.put(cacheKey, Boolean.TRUE); // 创建代理 Object proxy = createProxy( bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean)); this.proxyTypes.put(cacheKey, proxy.getClass()); return proxy; } // 缓存 this.advisedBeans.put(cacheKey, Boolean.FALSE); return bean;} |
org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#createProxy
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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); } // 创建代理工厂 ProxyFactory proxyFactory = new ProxyFactory(); proxyFactory.copyFrom(this); if (!proxyFactory.isProxyTargetClass()) { // 进来说明proxyTargetClass=false，指定JDK代理 if (shouldProxyTargetClass(beanClass, beanName)) { // 进来这里说明BD中有个属性preserveTargetClass=true，可以BD中属性设置的优先级最高 proxyFactory.setProxyTargetClass(true); } else { // 这里会判断bean有没有实现接口，没有就只能使用CGlib evaluateProxyInterfaces(beanClass, proxyFactory); } } Advisor[] advisors = buildAdvisors(beanName, specificInterceptors); proxyFactory.addAdvisors(advisors); // 切面 proxyFactory.setTargetSource(targetSource); // 目标对象 customizeProxyFactory(proxyFactory); proxyFactory.setFrozen(this.freezeProxy); if (advisorsPreFiltered()) { proxyFactory.setPreFiltered(true); } // 使用JDK或者CGlib创建代理对象 return proxyFactory.getProxy(getProxyClassLoader());} |
org.springframework.aop.framework.JdkDynamicAopProxy#getProxy(java.lang.ClassLoader)
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public Object getProxy(@Nullable ClassLoader classLoader) { if (logger.isTraceEnabled()) { logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource()); } Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true); findDefinedEqualsAndHashCodeMethods(proxiedInterfaces); return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);} |
这里主要看JDK动态代理的实现，Proxy.newProxyInstance()的第三个参数为InvocationHandler，而这里传的是this，也就是当前的类肯定实现了InvocationHandler接口。
代理方法的执行
由于是JDK动态代理，那么代理方法的调用肯定会进入InvocationHandler.invoke()方法中，这里的InvocationHandler的实现类为org.springframework.aop.framework.JdkDynamicAopProxy。
org.springframework.aop.framework.JdkDynamicAopProxy#invoke
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public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { 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(); // 目标对象 Class<?> targetClass = (target != null ? target.getClass() : null); // 目标对象的类型 // Get the interception chain for this method. // 这里会对方法进行匹配，因为不是目标对象中的所有方法都需要增强 List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass); // Check whether we have any advice. If we don't, we can fallback on direct // reflective invocation of the target, and avoid creating a MethodInvocation. if (chain.isEmpty()) { // We can skip creating a MethodInvocation: just invoke the target directly // Note that the final invoker must be an InvokerInterceptor so we know it does // nothing but a reflective operation on the target, and no hot swapping or fancy proxying. // 没有匹配的切面，直接通过反射调用目标对象的目标方法 Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args); retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse); } else { // We need to create a method invocation... MethodInvocation invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain); // Proceed to the joinpoint through the interceptor chain. /** * @see ReflectiveMethodInvocation#proceed() */ // 这里才是增强的调用，重点，火炬的传递 retVal = invocation.proceed(); } // Massage return value if necessary. Class<?> returnType = method.getReturnType(); if (retVal != null && retVal == target && returnType != Object.class && returnType.isInstance(proxy) && !RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) { // Special case: it returned "this" and the return type of the method // is type-compatible. Note that we can't help if the target sets // a reference to itself in another returned object. retVal = proxy; } else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) { throw new AopInvocationException( "Null return value from advice does not match primitive return type for: " + method); } return retVal; } finally { if (target != null && !targetSource.isStatic()) { // Must have come from TargetSource. targetSource.releaseTarget(target); } if (setProxyContext) { // Restore old proxy. AopContext.setCurrentProxy(oldProxy); } }} |
org.springframework.aop.framework.ReflectiveMethodInvocation#proceed
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public Object proceed() throws Throwable { // We start with an index of -1 and increment early. if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) { // 执行到最后一个Advice，才会到这里执行目标方法 return invokeJoinpoint(); } Object interceptorOrInterceptionAdvice = this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex); if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) { // Evaluate dynamic method matcher here: static part will already have // been evaluated and found to match. // dm.isRuntime()=true的走这 InterceptorAndDynamicMethodMatcher dm = (InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice; Class<?> targetClass = (this.targetClass != null ? this.targetClass : this.method.getDeclaringClass()); if (dm.methodMatcher.matches(this.method, targetClass, this.arguments)) { return dm.interceptor.invoke(this); } else { // Dynamic matching failed. // Skip this interceptor and invoke the next in the chain. return proceed(); } } else { // It's an interceptor, so we just invoke it: The pointcut will have // been evaluated statically before this object was constructed. // 走这 return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this); }} |
interceptorsAndDynamicMethodMatchers中第一个advice为org.springframework.aop.interceptor.ExposeInvocationInterceptor。
ExposeInvocationInterceptor#invoke
org.springframework.aop.interceptor.ExposeInvocationInterceptor#invoke
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private static final ThreadLocal<MethodInvocation> invocation = new NamedThreadLocal<>("Current AOP method invocation");public Object invoke(MethodInvocation mi) throws Throwable { MethodInvocation oldInvocation = invocation.get(); invocation.set(mi); try { return mi.proceed(); } finally { invocation.set(oldInvocation); }} |
ExposeInvocationInterceptor#invoke，只干了一件事就是将MethodInvocation加入到了ThreadLocal中，这样后续可以在其他地方使用ExposeInvocationInterceptor#currentInvocation获取到MethodInvocation，而MethodInvocation中封装了目标对象，目标方法，方法参数等信息。
环绕通知的执行
org.springframework.aop.aspectj.AspectJAroundAdvice#invoke
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public Object invoke(MethodInvocation mi) throws Throwable { if (!(mi instanceof ProxyMethodInvocation)) { throw new IllegalStateException("MethodInvocation is not a Spring ProxyMethodInvocation: " + mi); } ProxyMethodInvocation pmi = (ProxyMethodInvocation) mi; ProceedingJoinPoint pjp = lazyGetProceedingJoinPoint(pmi); JoinPointMatch jpm = getJoinPointMatch(pmi); return invokeAdviceMethod(pjp, jpm, null, null);} |
这里会去调用环绕通知的增强方法，而环绕通知的增强方法中会执行proceedingJoinPoint.proceed()，这样就会调用下一个MethodInterceptor–>MethodBeforeAdviceInterceptor。
前置通知的执行
org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor
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public Object invoke(MethodInvocation mi) throws Throwable { this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis()); return mi.proceed();} |
这里又会调用MethodInvocation.proceed()传递给下一个MethodInterceptor。
后置通知的执行
org.springframework.aop.aspectj.AspectJAfterAdvice#invoke
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public Object invoke(MethodInvocation mi) throws Throwable { try { return mi.proceed(); } finally { invokeAdviceMethod(getJoinPointMatch(), null, null); }} |
先执行MethodInvocation.proceed()，最后在finally块中调用后置通知的增强，不管目标方法有没有抛出异常，finally代码块中的代码都会执行，也就是不管目标方法有没有抛出异常，后置通知都会执行。
返回后通知的执行
org.springframework.aop.framework.adapter.AfterReturningAdviceInterceptor#invoke
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public Object invoke(MethodInvocation mi) throws Throwable { Object retVal = mi.proceed(); this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis()); return retVal;} |
先执行MethodInvocation.proceed()，然后再执行返回后通知的增强。
异常通知的执行
org.springframework.aop.aspectj.AspectJAfterThrowingAdvice#invoke
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public Object invoke(MethodInvocation mi) throws Throwable { try { return mi.proceed(); } catch (Throwable ex) { if (shouldInvokeOnThrowing(ex)) { invokeAdviceMethod(getJoinPointMatch(), null, ex); } throw ex; }} |
先执行MethodInvocation.proceed()，如果目标方法抛出了异常就会执行异常通知的增强，然后抛出异常，所以这时返回后通知的增强就不会执行了。
总结各种通知的执行顺序：
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Around begin // 环绕通知开始Before // 前置通知UserServiceImpl // 目标方法的执行AfterReturning // 返回后通知After // 后置通知Around end // 环绕通知结束 |
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原文链接：https://blog.csdn.net/u022812849/article/details/124167148
