spring aop （上中）获取Bean的增强

平凡的学生族

发布于 2019-06-03 08:47:21

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发布于 2019-06-03 08:47:21

文章被收录于专栏：后端技术后端技术

生成aop代理对象生成aop拦截链调用

《Spring技术内幕》学习笔记8——创建AOP代理对象并对目标对象切面拦截

spring boot 源码解析20-spring boot aop自动化配置 @EnableAspectJAutoProxy被自动配置，并注册id为org.springframework.aop.config.internalAutoProxyCreator的Bean。如果Bean已存在则根据优先级替换。这个Bean的class一般都是AnnotationAwareAspectJAutoProxyCreator(它会被AspectJAutoProxyRegistrar注册，而刚好又优先级最高，所以注册后也不会被取代)。总而言之一句话，注册了个AnnotationAwareAspectJAutoProxyCreator的Bean，它是一个BeanPostProcessor。我们可以猜到，这个后置处理器会对Bean生成代理。
Spring AOP 注解方式源码解析虽然起点是从xml开始解析的，但最终也会生成AnnotationAwareAspectJAutoProxyCreator。我最后看的这篇。

AnnotationAwareAspectJAutoProxyCreator

postProcessAfterInitialization->wrapIfNecessary:

protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
    ...

    // 获取Bean的增强
    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;
    }

    ...
}

会对Bean获取增强，再创建代理。所以我们主要研究getAdvicesAndAdvisorsForBean和createProxy。本文先研究获取Bean的增强。

AbstractAdvisorAutoProxyCreator.getAdvicesAndAdvisorsForBean

getAdvicesAndAdvisorsForBean->findEligibleAdvisors，其中

findCandidateAdvisors找到候选的Advisor
findAdvisorsThatCanApply筛选出能应用在该Bean上的Advisor
对增强进行扩展和排序

找到候选Advisor

findCandidateAdvisors

getAdvisors: 为切面的每个通知方法，生成InstantiationModelAwarePointcutAdvisorImpl这个Advisor,其构造函数中，会调用getAdvice根据注解生成对应Advice：

@Override
@Nullable
public Advice getAdvice(Method candidateAdviceMethod, AspectJExpressionPointcut expressionPointcut,
        MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {

    Class<?> candidateAspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
    validate(candidateAspectClass);

    AspectJAnnotation<?> aspectJAnnotation =
            AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
            
    ...

    AbstractAspectJAdvice springAdvice;

    switch (aspectJAnnotation.getAnnotationType()) {
        case AtPointcut:
            if (logger.isDebugEnabled()) {
                logger.debug("Processing pointcut '" + candidateAdviceMethod.getName() + "'");
            }
            return null;
        case AtAround:
            springAdvice = new AspectJAroundAdvice(
                    candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
            break;
        case AtBefore:
            springAdvice = new AspectJMethodBeforeAdvice(
                    candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
            break;
        case AtAfter:
            springAdvice = new AspectJAfterAdvice(
                    candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
            break;
        case AtAfterReturning:
            springAdvice = new AspectJAfterReturningAdvice(
                    candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
            AfterReturning afterReturningAnnotation = (AfterReturning) aspectJAnnotation.getAnnotation();
            if (StringUtils.hasText(afterReturningAnnotation.returning())) {
                springAdvice.setReturningName(afterReturningAnnotation.returning());
            }
            break;
        case AtAfterThrowing:
            springAdvice = new AspectJAfterThrowingAdvice(
                    candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
            AfterThrowing afterThrowingAnnotation = (AfterThrowing) aspectJAnnotation.getAnnotation();
            if (StringUtils.hasText(afterThrowingAnnotation.throwing())) {
                springAdvice.setThrowingName(afterThrowingAnnotation.throwing());
            }
            break;
        default:
            throw new UnsupportedOperationException(
                    "Unsupported advice type on method: " + candidateAdviceMethod);
    }

    // Now to configure the advice...
    springAdvice.setAspectName(aspectName);
    springAdvice.setDeclarationOrder(declarationOrder);
    String[] argNames = this.parameterNameDiscoverer.getParameterNames(candidateAdviceMethod);
    if (argNames != null) {
        springAdvice.setArgumentNamesFromStringArray(argNames);
    }
    springAdvice.calculateArgumentBindings();

    return springAdvice;
}