Spring配置文件解析之BeanDefinitionDocumentReader详解

public interface BeanDefinitionDocumentReader {
 
	void registerBeanDefinitions(Document doc, XmlReaderContext readerContext)
			throws BeanDefinitionStoreException;
 
}

	@Override
	public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
		this.readerContext = readerContext;
		logger.debug("Loading bean definitions");
		Element root = doc.getDocumentElement();
		doRegisterBeanDefinitions(root);
	}

protected void doRegisterBeanDefinitions(Element root) {
		
		BeanDefinitionParserDelegate parent = this.delegate;
		//创建BeanDefinitionParserDelegate，真正xml中各种元素的解析
		this.delegate = createDelegate(getReaderContext(), root, parent);
 
		if (this.delegate.isDefaultNamespace(root)) {
			String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
			if (StringUtils.hasText(profileSpec)) {
				String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
						profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
				if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
					if (logger.isInfoEnabled()) {
						logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec +
								"] not matching: " + getReaderContext().getResource());
					}
					return;
				}
			}
		}
 
		preProcessXml(root);
		parseBeanDefinitions(root, this.delegate);
		postProcessXml(root);
 
		this.delegate = parent;
	}

protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
		if (delegate.isDefaultNamespace(root)) {
			NodeList nl = root.getChildNodes();
			for (int i = 0; i < nl.getLength(); i++) {
				Node node = nl.item(i);
				if (node instanceof Element) {
					Element ele = (Element) node;
					if (delegate.isDefaultNamespace(ele)) {
						//默认的一些标签在DefaultBeanDefinitionDocumentReader进行解析
						parseDefaultElement(ele, delegate);
					}
					else {
						//如果不是默认的就需要在通过委派模式来寻找解析处理器
						delegate.parseCustomElement(ele);
					}
				}
			}
		}
		else {
			//如果不是默认的就需要在通过委派模式来寻找解析处理器
			delegate.parseCustomElement(root);
		}
	}

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
		//解析import标签
		if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
			importBeanDefinitionResource(ele);
		}
		//解析alias标签
		else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
			processAliasRegistration(ele);
		}
		//解析bean标签
		else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
			processBeanDefinition(ele, delegate);
		}
		//解析beans标签，就是进行递归解析
		else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
			// recurse
			doRegisterBeanDefinitions(ele);
		}
	}
 

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
		//最终还是在BeanDefinitionParserDelegate中进行元素解析
		//BeanDefinitionHolder是对BeanDefinition的封装，包括BeanDefinition，beanName,aliases
		BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
		if (bdHolder != null) {
			bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
			try {
				//处理的操作是将bean的元数据BeanDifinition注册到BeanFactory中
				BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
			}
			catch (BeanDefinitionStoreException ex) {
				getReaderContext().error("Failed to register bean definition with name '" +
						bdHolder.getBeanName() + "'", ele, ex);
			}
			// Send registration event.
			getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
		}
	}