关于java:一AOP-如何注入SpringBoot中

次要内容

SpringBoot如何将AOP相干的类注入BeanFactory中，如何起作用呢？

梳理概要

1. AopAutoConfiguration：主动注入AOP相干的配置类；AnnotationAwareAspectJAutoProxyCreator;
2. 在populateBean的时候，每个bean都会扫描是否有切面，匹配一下；AnnotationAwareAspectJAutoProxyCreator.postProcessAfterInitialization；
3. 匹配胜利，则会通过cglib动静代理生成一个新的代理类；

具体的源码过程

1.1 主动配置类加载AOP相干的类；

1. 加载AopAutoConfiguration

2. 在加载CglibAutoProxyFactory的时候，外面有注解@EnableAspectJAutoProxy的时候有一个@Import注解，AspectJAutoProxyRegistrar；这个Registrar很重要！！！
   
   其在ConfigurationClassPostProcessor类扫描加载bean的时候，解决loadBeanDefinitionsFromRegistrars的时候；加载进去；

   public void registerBeanDefinitions(
            AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
   
        AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry);
   .....

   registerAspectJAnnotationAutoProxyCreatorIfNecessary()的时候，
   把AnnotationAwareAspectJAutoProxyCreator封装成BeanDefinition，对应的key=internalAutoProxyCreator；

   @Nullable
    public static BeanDefinition registerAspectJAnnotationAutoProxyCreatorIfNecessary(
            BeanDefinitionRegistry registry, @Nullable Object source) {
   // 把AnnotationAwareAspectJAutoProxyCreator封装成一个BeanDefinition；
        return registerOrEscalateApcAsRequired(AnnotationAwareAspectJAutoProxyCreator.class, registry, source);
    }

1.2 应用代理类（AnnotationAwareAspectJAutoProxyCreator）

InitializeBean — 初始化bean的时候，会对立调用所有的BeanPostProcessor.postProcessAfterInitialization；其中就会调用到AnnotationAwareAspectJAutoProxyCreator；进行查看是否有符合要求的切面办法；
调用办法如下：

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

// 重点如下：找到这个bean的所有切面办法，而后调用createProxy创立代理类；返回即可。
        // Create proxy if we have advice.
        Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
        if (specificInterceptors != DO_NOT_PROXY) {
            this.advisedBeans.put(cacheKey, Boolean.TRUE);
            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;
    }

1.3 找所有的适合的告诉

protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
// 1 找到所有的候选告诉
        List<Advisor> candidateAdvisors = findCandidateAdvisors();
// 2 进行匹配，查看是否适合
        List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
        extendAdvisors(eligibleAdvisors);
        if (!eligibleAdvisors.isEmpty()) {
// 3 这里排序Advisor？
            eligibleAdvisors = sortAdvisors(eligibleAdvisors);
        }
        return eligibleAdvisors;
    }

1.3.1 findCandidateAdvisors

    protected List<Advisor> findCandidateAdvisors() {
        // Add all the Spring advisors found according to superclass rules.
// 从所有带@Advisor注解的切面类；
        List<Advisor> advisors = super.findCandidateAdvisors();
        // Build Advisors for all AspectJ aspects in the bean factory.
        if (this.aspectJAdvisorsBuilder != null) {
// 开始找@AspectJ的注解类；            advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors());
        }
        return advisors;
    }

this.aspectJAdvisorsBuilder.buildAspectJAdvisors()
次要逻辑：

1. 遍历BeanDefinitionMap，查看是否有@AspectJ注解，
2. 如果有，则会遍历method，查看是否是一个告诉，如果是一个告诉，则会封装成一个InstantiationModelAwarePointcutAdvisorImpl类；

3. 而后封装返回；
   在这个办法外面还有一个排序！！ 在getAdvisorMethod中

   private List<Method> getAdvisorMethods(Class<?> aspectClass) {
        List<Method> methods = new ArrayList<>();
        ReflectionUtils.doWithMethods(aspectClass, methods::add, adviceMethodFilter);
        if (methods.size() > 1) {
            methods.sort(adviceMethodComparator);
        }
        return methods;
    }
   

依照什么排序呢？

    private static final Comparator<Method> adviceMethodComparator;

    static {
        // Note: although @After is ordered before @AfterReturning and @AfterThrowing,
        // an @After advice method will actually be invoked after @AfterReturning and
        // @AfterThrowing methods due to the fact that AspectJAfterAdvice.invoke(MethodInvocation)
        // invokes proceed() in a `try` block and only invokes the @After advice method
        // in a corresponding `finally` block.
        Comparator<Method> adviceKindComparator = new ConvertingComparator<>(
                new InstanceComparator<>(
                        Around.class, Before.class, After.class, AfterReturning.class, AfterThrowing.class),
                (Converter<Method, Annotation>) method -> {
                    AspectJAnnotation<?> ann = AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(method);
                    return (ann != null ? ann.getAnnotation() : null);
                });
        Comparator<Method> methodNameComparator = new ConvertingComparator<>(Method::getName);
        adviceMethodComparator = adviceKindComparator.thenComparing(methodNameComparator);
    }

咱们发现，他是依照Around、Before、After、AfterReturning进行排序，如果有雷同，则依照methodName进行排序；

1.3.2 findAdvisorsThatCanApply

查看这个类是否和PointCut 匹配胜利，匹配胜利，即返回列表；

    protected List<Advisor> findAdvisorsThatCanApply(
            List<Advisor> candidateAdvisors, Class<?> beanClass, String beanName) {

        ProxyCreationContext.setCurrentProxiedBeanName(beanName);
        try {
// 查看这个类是否和PointCut 匹配胜利，匹配胜利，即ok；
            return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
        }
        finally {
            ProxyCreationContext.setCurrentProxiedBeanName(null);
        }
    }

1.3.3 findAdvisorsThatCanApply

比拟两个类的order大小；

1.4 createProxy

这个不在细追，
主题逻辑：

1. 找到所有的Advisor
2. 创立指定的拦截器，比方：dynamicAdvisorInterceptor退出到callback办法中；
3. Enhancer.create();

总结

1. 先想好，再去做；
2. 命名艺术，AutoProxyCreator、AspectJAdvisor、AspectJAdvisorBuilder、XXFactory
3. 封装成对象，便于当前的扩大