【Spring实战】Spring注解配置工作原理源码解析

registerComponents(parserContext.getReaderContext(), beanDefinitions, element);

protected void registerComponents(
			XmlReaderContext readerContext, Set<BeanDefinitionHolder> beanDefinitions, Element element) {
		Object source = readerContext.extractSource(element);
		CompositeComponentDefinition compositeDef = new CompositeComponentDefinition(element.getTagName(), source);
		for (BeanDefinitionHolder beanDefHolder : beanDefinitions) {
			compositeDef.addNestedComponent(new BeanComponentDefinition(beanDefHolder));
		}
		// Register annotation config processors, if necessary.
		boolean annotationConfig = true;
		if (element.hasAttribute(ANNOTATION_CONFIG_ATTRIBUTE)) {  //本例中没有配置annotation-config，默认为true
			annotationConfig = Boolean.valueOf(element.getAttribute(ANNOTATION_CONFIG_ATTRIBUTE));
		}
		if (annotationConfig) {
			Set<BeanDefinitionHolder> processorDefinitions =
					AnnotationConfigUtils.registerAnnotationConfigProcessors(readerContext.getRegistry(), source);  //注册注解处理器
			for (BeanDefinitionHolder processorDefinition : processorDefinitions) {
				compositeDef.addNestedComponent(new BeanComponentDefinition(processorDefinition));
			}
		}
		readerContext.fireComponentRegistered(compositeDef);         //目前没啥卵用，EmptyReaderEventListener.java中都是空操作，扩展用
	}

上述代码的作用主要是注册注解处理器，本例中没有配置annotation-config，默认值为true，这里也就说明了为什么配置了<context:component-scan>标签就不需要再配置<context:annotation-config>标签的原因。看下注册注解处理器：