Spring--默认标签的解析

1 在DefaultBeanDefinitionDocumentReader的方法parseBeanDefinitions中对于标签的解析分为默认标签的解析和自定义标签的解析。而默认标签与自定义标签的的区分是根据命名空间来进行判断的。具体代码如下

BeanDefinitionParserDelegate类
public static final String BEANS_NAMESPACE_URI = "http://www.springframework.org/schema/beans";
public boolean isDefaultNamespace(String namespaceUri) {
		return (!StringUtils.hasLength(namespaceUri) || BEANS_NAMESPACE_URI.equals(namespaceUri));
	}

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)) {
						//默认标签的解析
						parseDefaultElement(ele, delegate);
					}
					else {
						//自定义标签的解析
						delegate.parseCustomElement(ele);
					}
				}
			}
		}
		else {
			//自定义标签的计息
			delegate.parseCustomElement(root);
		}
	}

默认标签的解析分为import、alias、bean、beans；对于beans标签及配置文件的最高父标签，采用深度优先遍历的方式，再次进入parseBeanDefinitions方法中进入解析。

2 bean标签的解析：BeanDefinitionParserDelegate-》parseBeanDefinitionElement

	public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
		String id = ele.getAttribute(ID_ATTRIBUTE);
		String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
		
		List aliases = new ArrayList();
		if (StringUtils.hasLength(nameAttr)) {
			String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
			aliases.addAll(Arrays.asList(nameArr));
		}
		//如果没有给id赋值，则将第一个name的值赋给id。
		String beanName = id;
		if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
			beanName = aliases.remove(0);
			if (logger.isDebugEnabled()) {
				logger.debug("No XML 'id' specified - using '" + beanName +
						"' as bean name and " + aliases + " as aliases");
			}
		}
		//对name和alias的值与已经解析完成后存于HashSet中的name的值进行比较，即唯一性比较，成功则添加到HashSet中。
		if (containingBean == null) {
			checkNameUniqueness(beanName, aliases, ele);
		}

		AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
		if (beanDefinition != null) {
			if (!StringUtils.hasText(beanName)) {
				try {
					if (containingBean != null) {
						beanName = BeanDefinitionReaderUtils.generateBeanName(
								beanDefinition, this.readerContext.getRegistry(), true);
					}
					else {
						beanName = this.readerContext.generateBeanName(beanDefinition);
						// Register an alias for the plain bean class name, if still possible,
						// if the generator returned the class name plus a suffix.
						// This is expected for Spring 1.2/2.0 backwards compatibility.
						String beanClassName = beanDefinition.getBeanClassName();
						if (beanClassName != null &&
								beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
								!this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
							aliases.add(beanClassName);
						}
					}
					if (logger.isDebugEnabled()) {
						logger.debug("Neither XML 'id' nor 'name' specified - " +
								"using generated bean name [" + beanName + "]");
					}
				}
				catch (Exception ex) {
					error(ex.getMessage(), ele);
					return null;
				}
			}
			String[] aliasesArray = StringUtils.toStringArray(aliases);
			return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
		}

		return null;
	}