dubbo起停之服务消费

Posted 2022-12-29 lccsblog

ReferenceAnnotationBeanPostProcessor继承了AnnotationInjectedBeanPostProcessors其实现了InstantiationAwareBeanPostProcessorAdapter接口postProcessPropertyValues方法中，扫描带@Reference注解的成员 注入ReferenceBean对象：

@Override
    public PropertyValues postProcessPropertyValues(
            PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeanCreationException 

        InjectionMetadata metadata = findInjectionMetadata(beanName, bean.getClass(), pvs);
        try 
            metadata.inject(bean, beanName, pvs);
         catch (BeanCreationException ex) 
            throw ex;
         catch (Throwable ex) 
            throw new BeanCreationException(beanName, "Injection of @" + getAnnotationType().getName()
                    + " dependencies is failed", ex);
        
        return pvs;

findInjectionMetadata会找出所有@Reference的字段和方法并封装成元数据，metadata.inject方法进去，会调用injectElement的inject方法，进而调用AnnotatedFieldElement的inject方法：

 public class AnnotatedFieldElement extends InjectionMetadata.InjectedElement 

        private final Field field;

        private final A annotation;

        private volatile Object bean;

        protected AnnotatedFieldElement(Field field, A annotation) 
            super(field, null);
            this.field = field;
            this.annotation = annotation;
        

        @Override
        protected void inject(Object bean, String beanName, PropertyValues pvs) throws Throwable 

            Class<?> injectedType = field.getType();

            Object injectedObject = getInjectedObject(annotation, bean, beanName, injectedType, this);

            ReflectionUtils.makeAccessible(field);

            field.set(bean, injectedObject);

        

    

 

 protected Object getInjectedObject(A annotation, Object bean, String beanName, Class<?> injectedType,
                                       InjectionMetadata.InjectedElement injectedElement) throws Exception 

        String cacheKey = buildInjectedObjectCacheKey(annotation, bean, beanName, injectedType, injectedElement);

        Object injectedObject = injectedObjectsCache.get(cacheKey);

        if (injectedObject == null) 
            injectedObject = doGetInjectedBean(annotation, bean, beanName, injectedType, injectedElement);
            // Customized inject-object if necessary
            injectedObjectsCache.putIfAbsent(cacheKey, injectedObject);
        

        return injectedObject;

    

其中doGetInjectedBean被ReferenceAnnotationBeanPostProcessor重写：

 @Override
    protected Object doGetInjectedBean(Reference reference, Object bean, String beanName, Class<?> injectedType,
                                       InjectionMetadata.InjectedElement injectedElement) throws Exception 

        String referencedBeanName = buildReferencedBeanName(reference, injectedType);

        ReferenceBean referenceBean = buildReferenceBeanIfAbsent(referencedBeanName, reference, injectedType, getClassLoader());

        cacheInjectedReferenceBean(referenceBean, injectedElement);

        Object proxy = buildProxy(referencedBeanName, referenceBean, injectedType);

        return proxy;
    

可以看到这里构造了一个referenceBean并返回了一个代理，真正注入的其实是这个代理