Spring源码浅析 -- XML配置文件的载入与解析_neither xml id nor name specified-优快云博客

本文深入探讨了Spring框架如何加载配置文件的过程，从创建ApplicationContext到解析XML配置，直至注册BeanDefinition，全面展示了配置文件的载入机制。

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最近在看Spring源代码，对配置文件信息的载入是使用Spring的第一步，而这第一步就是一个非常复杂的过程....
Spring通过定义BeanDefination来管理Ioc中的各种对象以及它们之间的依赖关系，所以载入的过程其实就是将XML文件读取并解析成BeanDefination数据的过程。
我们以最常使用的ClassPathXmlApplicationContext为切入点

1. 创建一个ClassPathXmlApplicationContext对象，传入文件路径

Java代码

ClassPathXmlApplicationContext re = new ClassPathXmlApplicationContext("applicationContext.xml");

ClassPathXmlApplicationContext re = new ClassPathXmlApplicationContext("applicationContext.xml");

这个构造方法会重载到

Java代码

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}

	public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
			throws BeansException {

		super(parent);
		setConfigLocations(configLocations);
		if (refresh) {
			refresh();
		}
	}

其中首先设置配置路径 setConfigLocations(configLocations) ，而后进行刷新 refresh()，而这个refresh()方法是Ioc容器初始化的入口

2.refresh方法的结构

refresh方法由AbstractApplicationContext实现

Java代码

public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
}
}

public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			prepareBeanFactory(beanFactory);

			try {
				// Allows post-processing of the bean factory in context subclasses.
				postProcessBeanFactory(beanFactory);

				// Invoke factory processors registered as beans in the context.
				invokeBeanFactoryPostProcessors(beanFactory);

				// Register bean processors that intercept bean creation.
				registerBeanPostProcessors(beanFactory);

				// Initialize message source for this context.
				initMessageSource();

				// Initialize event multicaster for this context.
				initApplicationEventMulticaster();

				// Initialize other special beans in specific context subclasses.
				onRefresh();

				// Check for listener beans and register them.
				registerListeners();

				// Instantiate all remaining (non-lazy-init) singletons.
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				finishRefresh();
			}

			catch (BeansException ex) {
				// Destroy already created singletons to avoid dangling resources.
				destroyBeans();

				// Reset 'active' flag.
				cancelRefresh(ex);

				// Propagate exception to caller.
				throw ex;
			}
		}
	}

这个方法中描述了ApplicationContext的整个初始化过程，包括BeanFactory的更新，还有messagesource以及一些生命周期有关属性的注册，而我们关心的是BeanFactory的更新，即obtainFreshBeanFactory()方法

3.启动对BeanDefination的载入

还是在ApplicationContext类中

Java代码

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}

	protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
		refreshBeanFactory();
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		if (logger.isDebugEnabled()) {
			logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
		}
		return beanFactory;
	}

它的第一步交给一个抽象方法refreshBeanFactory()，具体的实现在AbstractRefreshableApplicationContext类中

Java代码

@Override
protected final void refreshBeanFactory() throws BeansException {
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
customizeBeanFactory(beanFactory);
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}

	@Override
	protected final void refreshBeanFactory() throws BeansException {
		if (hasBeanFactory()) {
			destroyBeans();
			closeBeanFactory();
		}
		try {
			DefaultListableBeanFactory beanFactory = createBeanFactory();
			beanFactory.setSerializationId(getId());
			customizeBeanFactory(beanFactory);
			loadBeanDefinitions(beanFactory);
			synchronized (this.beanFactoryMonitor) {
				this.beanFactory = beanFactory;
			}
		}
		catch (IOException ex) {
			throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
		}
	}

第一步是判断是否已经创建过BeanFactory，如果是，将它销毁，重新创建
第二步就是创建各种ApplicationContext持有的真正容器实现类DefaultListableBeanFactory，创建Ioc容器

最后启动BeanDefination的载入 loadBeanDefinitions(beanFactory)方法

4.BeanFactory将载入工作交给BeanDefinationReader

loadBeanDefinitions(beanFactory)方法是抽象的，又因为我们的配置文件是XML格式的，所以具体实现实在AbstractXmlApplicationConext中

Java代码

@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
initBeanDefinitionReader(beanDefinitionReader);
loadBeanDefinitions(beanDefinitionReader);
}

	@Override
	protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
		// Create a new XmlBeanDefinitionReader for the given BeanFactory.
		XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

		// Configure the bean definition reader with this context's
		// resource loading environment.
		beanDefinitionReader.setResourceLoader(this);
		beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

		// Allow a subclass to provide custom initialization of the reader,
		// then proceed with actually loading the bean definitions.
		initBeanDefinitionReader(beanDefinitionReader);
		loadBeanDefinitions(beanDefinitionReader);
	}

这里创建了一个XmlBeanDefinitionReader 对象，它专门用来读取基于XML文件格式的BeanDefinition配置，接下来重载到loadBeanDefinitions(beanDefinitionReader);

Java代码

protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
Resource[] configResources = getConfigResources();
if (configResources != null) {
reader.loadBeanDefinitions(configResources);
}
String[] configLocations = getConfigLocations();
if (configLocations != null) {
reader.loadBeanDefinitions(configLocations);
}
}

	protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
		Resource[] configResources = getConfigResources();
		if (configResources != null) {
			reader.loadBeanDefinitions(configResources);
		}
		String[] configLocations = getConfigLocations();
		if (configLocations != null) {
			reader.loadBeanDefinitions(configLocations);
		}
	}

首先载入Resource对象用来定位资源，Resource对象的生成在ClassPathXmlApplicationContext 中setConfigLocations(configLocations)方法实现

然后调用XmlBeanDefinitionReader基类AbstractBeanDefinitionReader的loadBeanDefinitions方法

Java代码

public int loadBeanDefinitions(Resource[] resources) throws BeanDefinitionStoreException {
Assert.notNull(resources, "Resource array must not be null");
int counter = 0;
for (Resource resource : resources) {
counter += loadBeanDefinitions(resource);
}
return counter;
}

	public int loadBeanDefinitions(Resource[] resources) throws BeanDefinitionStoreException {
		Assert.notNull(resources, "Resource array must not be null");
		int counter = 0;
		for (Resource resource : resources) {
			counter += loadBeanDefinitions(resource);
		}
		return counter;
	}

然后调用loadBeanDefinitions(resource)方法，此方法的具体实现在XmlBeanDefinitionReader 中

Java代码

public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
return loadBeanDefinitions(new EncodedResource(resource));
}

	public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
		return loadBeanDefinitions(new EncodedResource(resource));
	}

重载到

Java代码

public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isInfoEnabled()) {
logger.info("Loading XML bean definitions from " + encodedResource.getResource());
}
Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (currentResources == null) {
currentResources = new HashSet<EncodedResource>(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException(
"Detected recursive loading of " + encodedResource + " - check your import definitions!");
}
try {
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}
finally {
inputStream.close();
}
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"IOException parsing XML document from " + encodedResource.getResource(), ex);
}
finally {
currentResources.remove(encodedResource);
if (currentResources.isEmpty()) {
this.resourcesCurrentlyBeingLoaded.set(null);
}
}
}

public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
		Assert.notNull(encodedResource, "EncodedResource must not be null");
		if (logger.isInfoEnabled()) {
			logger.info("Loading XML bean definitions from " + encodedResource.getResource());
		}

		Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
		if (currentResources == null) {
			currentResources = new HashSet<EncodedResource>(4);
			this.resourcesCurrentlyBeingLoaded.set(currentResources);
		}
		if (!currentResources.add(encodedResource)) {
			throw new BeanDefinitionStoreException(
					"Detected recursive loading of " + encodedResource + " - check your import definitions!");
		}
		try {
			InputStream inputStream = encodedResource.getResource().getInputStream();
			try {
				InputSource inputSource = new InputSource(inputStream);
				if (encodedResource.getEncoding() != null) {
					inputSource.setEncoding(encodedResource.getEncoding());
				}
				return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
			}
			finally {
				inputStream.close();
			}
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException(
					"IOException parsing XML document from " + encodedResource.getResource(), ex);
		}
		finally {
			currentResources.remove(encodedResource);
			if (currentResources.isEmpty()) {
				this.resourcesCurrentlyBeingLoaded.set(null);
			}
		}
	}

在此类中主要是对输入流进行编码操作，然后调用doLoadBeanDefinitions(inputSource, encodedResource.getResource())方法

5.XmlBeanDefinitionReader将载入工作交给W3C的dom

因为读入的文件是XML格式的，所以底层的实现肯定是要和W3C的dom结构打交道

doLoadBeanDefinitions(inputSource, encodedResource.getResource())方法正式引入dom

Java代码

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
int validationMode = getValidationModeForResource(resource);
Document doc = this.documentLoader.loadDocument(
inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());
return registerBeanDefinitions(doc, resource);
}
catch (BeanDefinitionStoreException ex) {
throw ex;
}
catch (SAXParseException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
}
catch (SAXException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"XML document from " + resource + " is invalid", ex);
}
catch (ParserConfigurationException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Parser configuration exception parsing XML from " + resource, ex);
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"IOException parsing XML document from " + resource, ex);
}
catch (Throwable ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Unexpected exception parsing XML document from " + resource, ex);
}
}

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
			throws BeanDefinitionStoreException {
		try {
			int validationMode = getValidationModeForResource(resource);
			Document doc = this.documentLoader.loadDocument(
					inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());
			return registerBeanDefinitions(doc, resource);
		}
		catch (BeanDefinitionStoreException ex) {
			throw ex;
		}
		catch (SAXParseException ex) {
			throw new XmlBeanDefinitionStoreException(resource.getDescription(),
					"Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
		}
		catch (SAXException ex) {
			throw new XmlBeanDefinitionStoreException(resource.getDescription(),
					"XML document from " + resource + " is invalid", ex);
		}
		catch (ParserConfigurationException ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"Parser configuration exception parsing XML from " + resource, ex);
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"IOException parsing XML document from " + resource, ex);
		}
		catch (Throwable ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"Unexpected exception parsing XML document from " + resource, ex);
		}
	}

在此方法中生成了Document类的对象，下一步是进行对象的注册，registerBeanDefinitions(doc, resource)方法

Java代码

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
// Read document based on new BeanDefinitionDocumentReader SPI.
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
int countBefore = getRegistry().getBeanDefinitionCount();
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}

	public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
		// Read document based on new BeanDefinitionDocumentReader SPI.
		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
		int countBefore = getRegistry().getBeanDefinitionCount();
		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
		return getRegistry().getBeanDefinitionCount() - countBefore;
	}

此方法统计了注册的BeanDefinition的个数，返回一个int值，而具体的注册工作在BeanDefinitionDocumentReader 接口的实现类DefaultBeanDefinitionDocumentReader 中registerBeanDefinitions(doc, createReaderContext(resource))方法实现

6.BeanDefinitionDocumentReader将载入工作交给代理类BeanDefinationParserDelegate

DefaultBeanDefinitionDocumentReader的registerBeanDefinitions(doc, createReaderContext(resource))方法

Java代码

public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
Element root = doc.getDocumentElement();
BeanDefinitionParserDelegate delegate = createHelper(readerContext, root);
preProcessXml(root);
parseBeanDefinitions(root, delegate);
postProcessXml(root);
}

	public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
		this.readerContext = readerContext;

		logger.debug("Loading bean definitions");
		Element root = doc.getDocumentElement();

		BeanDefinitionParserDelegate delegate = createHelper(readerContext, root);

		preProcessXml(root);
		parseBeanDefinitions(root, delegate);
		postProcessXml(root);
	}

其中首先得到dom结构的根，然后由根进行分析

然后引入BeanDefinitionParserDelegate 代理类对dom结构进行分析，调用parseBeanDefinitions(root, delegate)方法

Java代码

protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
if (delegate.isDefaultNamespace(delegate.getNamespaceURI(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;
String namespaceUri = delegate.getNamespaceURI(ele);
if (delegate.isDefaultNamespace(namespaceUri)) {
parseDefaultElement(ele, delegate);
}
else {
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}

	protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
		if (delegate.isDefaultNamespace(delegate.getNamespaceURI(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;
					String namespaceUri = delegate.getNamespaceURI(ele);
					if (delegate.isDefaultNamespace(namespaceUri)) {
						parseDefaultElement(ele, delegate);
					}
					else {
						delegate.parseCustomElement(ele);
					}
				}
			}
		}
		else {
			delegate.parseCustomElement(root);
		}
	}

其中最主要的操作是在调用parseDefaultElement(ele, delegate)方法中进行

Java代码

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
}

	private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
		if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
			importBeanDefinitionResource(ele);
		}
		else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
			processAliasRegistration(ele);
		}
		else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
			processBeanDefinition(ele, delegate);
		}
	}

从这个方法里面我们就能看出来底层元素的端倪了，首先判断Node是否为import节点，然后是alias节点，最后是bean节点，我们关心的是bean节点，processBeanDefinition(ele, delegate)方法

Java代码

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// Register the final decorated instance.
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));
}
}

	protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
		BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
		if (bdHolder != null) {
			bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
			try {
				// Register the final decorated instance.
				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));
		}
	}

这里首先由BeanDefinitionParserDelegate 生成BeanDefination的包装类BeanDefinitionHolder ，然后再进行一些修饰工作，这里把工作正式交给BeanDefinitionParserDelegate

7.BeanDefinitionParserDelegate 中的解析工作

BeanDefinition的解析主要在BeanDefinitionParserDelegate 的parseBeanDefinitionElement(ele)方法中进行，重载到

Java代码

public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
String id = ele.getAttribute(ID_ATTRIBUTE);
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
List<String> aliases = new ArrayList<String>();
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, BEAN_NAME_DELIMITERS);
aliases.addAll(Arrays.asList(nameArr));
}
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");
}
}
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;
}

	public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
		String id = ele.getAttribute(ID_ATTRIBUTE);
		String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);

		List<String> aliases = new ArrayList<String>();
		if (StringUtils.hasLength(nameAttr)) {
			String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, BEAN_NAME_DELIMITERS);
			aliases.addAll(Arrays.asList(nameArr));
		}

		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");
			}
		}

		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;
	}

这个方法首先得到元素的name和id以及别名属性，然后再生成底层的AbstractBeanDefinition对象将它们包装生成BeanDefinitionHolder，其中包括bean的名称，别名，以及BeanDefinition，返回给上层方法

核心在于生成BeanDefinition的parseBeanDefinitionElement(ele, beanName, containingBean)方法

Java代码

public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
String className = null;
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
try {
String parent = null;
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
parseMetaElements(ele, bd);
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
parseConstructorArgElements(ele, bd);
parsePropertyElements(ele, bd);
parseQualifierElements(ele, bd);
bd.setResource(this.readerContext.getResource());
bd.setSource(extractSource(ele));
return bd;
}
catch (ClassNotFoundException ex) {
error("Bean class [" + className + "] not found", ele, ex);
}
catch (NoClassDefFoundError err) {
error("Class that bean class [" + className + "] depends on not found", ele, err);
}
catch (Throwable ex) {
error("Unexpected failure during bean definition parsing", ele, ex);
}
finally {
this.parseState.pop();
}
return null;
}

	public AbstractBeanDefinition parseBeanDefinitionElement(
			Element ele, String beanName, BeanDefinition containingBean) {

		this.parseState.push(new BeanEntry(beanName));

		String className = null;
		if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
			className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
		}

		try {
			String parent = null;
			if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
				parent = ele.getAttribute(PARENT_ATTRIBUTE);
			}
			AbstractBeanDefinition bd = createBeanDefinition(className, parent);

			parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
			bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));

			parseMetaElements(ele, bd);
			parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
			parseReplacedMethodSubElements(ele, bd.getMethodOverrides());

			parseConstructorArgElements(ele, bd);
			parsePropertyElements(ele, bd);
			parseQualifierElements(ele, bd);

			bd.setResource(this.readerContext.getResource());
			bd.setSource(extractSource(ele));

			return bd;
		}
		catch (ClassNotFoundException ex) {
			error("Bean class [" + className + "] not found", ele, ex);
		}
		catch (NoClassDefFoundError err) {
			error("Class that bean class [" + className + "] depends on not found", ele, err);
		}
		catch (Throwable ex) {
			error("Unexpected failure during bean definition parsing", ele, ex);
		}
		finally {
			this.parseState.pop();
		}

		return null;
	}

这个方法我们看起来一目了然，全部都是bean节点中的配置信息

首先得到class的名字，然后得到继承的parent的名字，然后是meta节点，look-up节点，replaced-method节点，构造函数设置节点，最后是比较复杂的property节点，我们继续分析比较复杂的property节点的解析，parsePropertyElements(ele, bd)方法

Java代码

public void parsePropertyElements(Element beanEle, BeanDefinition bd) {
NodeList nl = beanEle.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (node instanceof Element && nodeNameEquals(node, PROPERTY_ELEMENT)) {
parsePropertyElement((Element) node, bd);
}
}
}

	public void parsePropertyElements(Element beanEle, BeanDefinition bd) {
		NodeList nl = beanEle.getChildNodes();
		for (int i = 0; i < nl.getLength(); i++) {
			Node node = nl.item(i);
			if (node instanceof Element && nodeNameEquals(node, PROPERTY_ELEMENT)) {
				parsePropertyElement((Element) node, bd);
			}
		}
	}

将bean节点的子元素逐个取出判断是否为property节点，然后进行解析，parsePropertyElement((Element) node, bd)方法

Java代码

public void parsePropertyElement(Element ele, BeanDefinition bd) {
String propertyName = ele.getAttribute(NAME_ATTRIBUTE);
if (!StringUtils.hasLength(propertyName)) {
error("Tag 'property' must have a 'name' attribute", ele);
return;
}
this.parseState.push(new PropertyEntry(propertyName));
try {
if (bd.getPropertyValues().contains(propertyName)) {
error("Multiple 'property' definitions for property '" + propertyName + "'", ele);
return;
}
Object val = parsePropertyValue(ele, bd, propertyName);
PropertyValue pv = new PropertyValue(propertyName, val);
parseMetaElements(ele, pv);
pv.setSource(extractSource(ele));
bd.getPropertyValues().addPropertyValue(pv);
}
finally {
this.parseState.pop();
}
}

	public void parsePropertyElement(Element ele, BeanDefinition bd) {
		String propertyName = ele.getAttribute(NAME_ATTRIBUTE);
		if (!StringUtils.hasLength(propertyName)) {
			error("Tag 'property' must have a 'name' attribute", ele);
			return;
		}
		this.parseState.push(new PropertyEntry(propertyName));
		try {
			if (bd.getPropertyValues().contains(propertyName)) {
				error("Multiple 'property' definitions for property '" + propertyName + "'", ele);
				return;
			}
			Object val = parsePropertyValue(ele, bd, propertyName);
			PropertyValue pv = new PropertyValue(propertyName, val);
			parseMetaElements(ele, pv);
			pv.setSource(extractSource(ele));
			bd.getPropertyValues().addPropertyValue(pv);
		}
		finally {
			this.parseState.pop();
		}
	}

解析的主要过程，首先判断是否重复，如果重复抛出异常，然后对property节点内部进行解析，最后加入到bean节点信息中，我们继续解析property节点内部，parsePropertyValue(ele, bd, propertyName)方法

Java代码

public Object parsePropertyValue(Element ele, BeanDefinition bd, String propertyName) {
String elementName = (propertyName != null) ?
"<property> element for property '" + propertyName + "'" :
"<constructor-arg> element";
// Should only have one child element: ref, value, list, etc.
NodeList nl = ele.getChildNodes();
Element subElement = null;
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (node instanceof Element && !nodeNameEquals(node, DESCRIPTION_ELEMENT) &&
!nodeNameEquals(node, META_ELEMENT)) {
// Child element is what we're looking for.
if (subElement != null) {
error(elementName + " must not contain more than one sub-element", ele);
}
else {
subElement = (Element) node;
}
}
}
boolean hasRefAttribute = ele.hasAttribute(REF_ATTRIBUTE);
boolean hasValueAttribute = ele.hasAttribute(VALUE_ATTRIBUTE);
if ((hasRefAttribute && hasValueAttribute) ||
((hasRefAttribute || hasValueAttribute) && subElement != null)) {
error(elementName +
" is only allowed to contain either 'ref' attribute OR 'value' attribute OR sub-element", ele);
}
if (hasRefAttribute) {
String refName = ele.getAttribute(REF_ATTRIBUTE);
if (!StringUtils.hasText(refName)) {
error(elementName + " contains empty 'ref' attribute", ele);
}
RuntimeBeanReference ref = new RuntimeBeanReference(refName);
ref.setSource(extractSource(ele));
return ref;
}
else if (hasValueAttribute) {
TypedStringValue valueHolder = new TypedStringValue(ele.getAttribute(VALUE_ATTRIBUTE));
valueHolder.setSource(extractSource(ele));
return valueHolder;
}
else if (subElement != null) {
return parsePropertySubElement(subElement, bd);
}
else {
// Neither child element nor "ref" or "value" attribute found.
error(elementName + " must specify a ref or value", ele);
return null;
}
}

	public Object parsePropertyValue(Element ele, BeanDefinition bd, String propertyName) {
		String elementName = (propertyName != null) ?
						"<property> element for property '" + propertyName + "'" :
						"<constructor-arg> element";

		// Should only have one child element: ref, value, list, etc.
		NodeList nl = ele.getChildNodes();
		Element subElement = null;
		for (int i = 0; i < nl.getLength(); i++) {
			Node node = nl.item(i);
			if (node instanceof Element && !nodeNameEquals(node, DESCRIPTION_ELEMENT) &&
					!nodeNameEquals(node, META_ELEMENT)) {
				// Child element is what we're looking for.
				if (subElement != null) {
					error(elementName + " must not contain more than one sub-element", ele);
				}
				else {
					subElement = (Element) node;
				}
			}
		}

		boolean hasRefAttribute = ele.hasAttribute(REF_ATTRIBUTE);
		boolean hasValueAttribute = ele.hasAttribute(VALUE_ATTRIBUTE);
		if ((hasRefAttribute && hasValueAttribute) ||
				((hasRefAttribute || hasValueAttribute) && subElement != null)) {
			error(elementName +
					" is only allowed to contain either 'ref' attribute OR 'value' attribute OR sub-element", ele);
		}

		if (hasRefAttribute) {
			String refName = ele.getAttribute(REF_ATTRIBUTE);
			if (!StringUtils.hasText(refName)) {
				error(elementName + " contains empty 'ref' attribute", ele);
			}
			RuntimeBeanReference ref = new RuntimeBeanReference(refName);
			ref.setSource(extractSource(ele));
			return ref;
		}
		else if (hasValueAttribute) {
			TypedStringValue valueHolder = new TypedStringValue(ele.getAttribute(VALUE_ATTRIBUTE));
			valueHolder.setSource(extractSource(ele));
			return valueHolder;
		}
		else if (subElement != null) {
			return parsePropertySubElement(subElement, bd);
		}
		else {
			// Neither child element nor "ref" or "value" attribute found.
			error(elementName + " must specify a ref or value", ele);
			return null;
		}
	}

property节点主要是value和ref属性的配置，所以此方法首先是配置以上两个属性，然后是分析property节点的子元素，parsePropertySubElement(subElement, bd)方法，重载到

Java代码

public Object parsePropertySubElement(Element ele, BeanDefinition bd, String defaultValueType) {
if (!isDefaultNamespace(getNamespaceURI(ele))) {
return parseNestedCustomElement(ele, bd);
}
else if (nodeNameEquals(ele, BEAN_ELEMENT)) {
BeanDefinitionHolder nestedBd = parseBeanDefinitionElement(ele, bd);
if (nestedBd != null) {
nestedBd = decorateBeanDefinitionIfRequired(ele, nestedBd, bd);
}
return nestedBd;
}
else if (nodeNameEquals(ele, REF_ELEMENT)) {
// A generic reference to any name of any bean.
String refName = ele.getAttribute(BEAN_REF_ATTRIBUTE);
boolean toParent = false;
if (!StringUtils.hasLength(refName)) {
// A reference to the id of another bean in the same XML file.
refName = ele.getAttribute(LOCAL_REF_ATTRIBUTE);
if (!StringUtils.hasLength(refName)) {
// A reference to the id of another bean in a parent context.
refName = ele.getAttribute(PARENT_REF_ATTRIBUTE);
toParent = true;
if (!StringUtils.hasLength(refName)) {
error("'bean', 'local' or 'parent' is required for <ref> element", ele);
return null;
}
}
}
if (!StringUtils.hasText(refName)) {
error("<ref> element contains empty target attribute", ele);
return null;
}
RuntimeBeanReference ref = new RuntimeBeanReference(refName, toParent);
ref.setSource(extractSource(ele));
return ref;
}
else if (nodeNameEquals(ele, IDREF_ELEMENT)) {
return parseIdRefElement(ele);
}
else if (nodeNameEquals(ele, VALUE_ELEMENT)) {
return parseValueElement(ele, defaultValueType);
}
else if (nodeNameEquals(ele, NULL_ELEMENT)) {
// It's a distinguished null value. Let's wrap it in a TypedStringValue
// object in order to preserve the source location.
TypedStringValue nullHolder = new TypedStringValue(null);
nullHolder.setSource(extractSource(ele));
return nullHolder;
}
else if (nodeNameEquals(ele, ARRAY_ELEMENT)) {
return parseArrayElement(ele, bd);
}
else if (nodeNameEquals(ele, LIST_ELEMENT)) {
return parseListElement(ele, bd);
}
else if (nodeNameEquals(ele, SET_ELEMENT)) {
return parseSetElement(ele, bd);
}
else if (nodeNameEquals(ele, MAP_ELEMENT)) {
return parseMapElement(ele, bd);
}
else if (nodeNameEquals(ele, PROPS_ELEMENT)) {
return parsePropsElement(ele);
}
else {
error("Unknown property sub-element: [" + ele.getNodeName() + "]", ele);
return null;
}
}

	public Object parsePropertySubElement(Element ele, BeanDefinition bd, String defaultValueType) {
		if (!isDefaultNamespace(getNamespaceURI(ele))) {
			return parseNestedCustomElement(ele, bd);
		}
		else if (nodeNameEquals(ele, BEAN_ELEMENT)) {
			BeanDefinitionHolder nestedBd = parseBeanDefinitionElement(ele, bd);
			if (nestedBd != null) {
				nestedBd = decorateBeanDefinitionIfRequired(ele, nestedBd, bd);
			}
			return nestedBd;
		}
		else if (nodeNameEquals(ele, REF_ELEMENT)) {
			// A generic reference to any name of any bean.
			String refName = ele.getAttribute(BEAN_REF_ATTRIBUTE);
			boolean toParent = false;
			if (!StringUtils.hasLength(refName)) {
				// A reference to the id of another bean in the same XML file.
				refName = ele.getAttribute(LOCAL_REF_ATTRIBUTE);
				if (!StringUtils.hasLength(refName)) {
					// A reference to the id of another bean in a parent context.
					refName = ele.getAttribute(PARENT_REF_ATTRIBUTE);
					toParent = true;
					if (!StringUtils.hasLength(refName)) {
						error("'bean', 'local' or 'parent' is required for <ref> element", ele);
						return null;
					}
				}
			}
			if (!StringUtils.hasText(refName)) {
				error("<ref> element contains empty target attribute", ele);
				return null;
			}
			RuntimeBeanReference ref = new RuntimeBeanReference(refName, toParent);
			ref.setSource(extractSource(ele));
			return ref;
		}
		else if (nodeNameEquals(ele, IDREF_ELEMENT)) {
			return parseIdRefElement(ele);
		}
		else if (nodeNameEquals(ele, VALUE_ELEMENT)) {
			return parseValueElement(ele, defaultValueType);
		}
		else if (nodeNameEquals(ele, NULL_ELEMENT)) {
			// It's a distinguished null value. Let's wrap it in a TypedStringValue
			// object in order to preserve the source location.
			TypedStringValue nullHolder = new TypedStringValue(null);
			nullHolder.setSource(extractSource(ele));
			return nullHolder;
		}
		else if (nodeNameEquals(ele, ARRAY_ELEMENT)) {
			return parseArrayElement(ele, bd);
		}
		else if (nodeNameEquals(ele, LIST_ELEMENT)) {
			return parseListElement(ele, bd);
		}
		else if (nodeNameEquals(ele, SET_ELEMENT)) {
			return parseSetElement(ele, bd);
		}
		else if (nodeNameEquals(ele, MAP_ELEMENT)) {
			return parseMapElement(ele, bd);
		}
		else if (nodeNameEquals(ele, PROPS_ELEMENT)) {
			return parsePropsElement(ele);
		}
		else {
			error("Unknown property sub-element: [" + ele.getNodeName() + "]", ele);
			return null;
		}
	}

这个方法内部也是一目了然，首先是配置property节点的内嵌bean，然后配置ref引用，然后是idref引用，接下来是内嵌的value元素，还有null元素，最后是一系列的复杂数据类型，array，list，set，map以及props。

到这里配置文件的载入基本上已经到底了，如果对以上元素的配置感兴趣的话，可以继续查看源代码。这里只是包含配置文件的载入过程，并不包括在Ioc容器中的注册，以及依赖注入的过程。