一文详解Spring是怎么读取配置Xml文件的

	@Override
	public void reGISterBeanDefinitions(Document doc, XmlReaderContext readerContext) {
		this.readerContext = readerContext;
		logger.debug("Loading bean definitions");
		// 从Document中获取Element
		Element root = doc.getDocumentElement();
		//注册BeanDefinitions
		doRegisterBeanDefinitions(root);
	}

protected void doRegisterBeanDefinitions(Element root) {
		BeanDefinitionParserDelegate parent = this.delegate;
		
		
		this.delegate = createDelegate(getReaderContext(), root, parent);
		//根据root查询 xml文件的命名空间是不是public static final String BEANS_NAMESPACE_URI = "Http://www.springframework.org/schema/beans";
		if (this.delegate.isDefaultNamespace(root)) {
			//省略.....
		}
		//默认空实现 子类可以重写这个方法来处理自定义xml文件
		preProcessXml(root);
		parseBeanDefinitions(root, this.delegate);
		//默认空实现 子类可以重写这个方法来处理自定义xml文件
		postProcessXml(root);

		this.delegate = parent;
	}

public void initDefaults(Element root, BeanDefinitionParserDelegate parent) {
		// this.defaults 是一个DocumentDefaultsDefinition对象；
		populateDefaults(this.defaults, (parent != null ? parent.defaults : null), root);
		this.readerContext.fireDefaultsRegistered(this.defaults);
	}

<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
	http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd"
	default-autowire="byName" default-lazy-init="false" default-dependency-check="all" >

//parentDefaults是父类的DocumentDefaultsDefinition对象
protected void populateDefaults(DocumentDefaultsDefinition defaults, DocumentDefaultsDefinition parentDefaults, Element root) {
		//查看xml文件中默认的default-lazy-init 值；(如果xml没有显示配置 则它的值为 default)懒加载的默认值
		String lazyInit = root.getAttribute(DEFAULT_LAZY_INIT_ATTRIBUTE);
		if (DEFAULT_VALUE.equals(lazyInit)) {
			//如果有父类,则以父类的为准，否则将返回false。
			lazyInit = (parentDefaults != null ? parentDefaults.getLazyInit() : FALSE_VALUE);
		}
		defaults.setLazyInit(lazyInit);
		//default-autowire-candidates
		String merge = root.getAttribute(DEFAULT_MERGE_ATTRIBUTE);
		if (DEFAULT_VALUE.equals(merge)) {
			// Potentially inherited from outer <beans> sections, otherwise falling back to false.
			merge = (parentDefaults != null ? parentDefaults.getMerge() : FALSE_VALUE);
		}
		defaults.setMerge(merge);
		//default-autowire
		String autowire = root.getAttribute(DEFAULT_AUTOWIRE_ATTRIBUTE);
		if (DEFAULT_VALUE.equals(autowire)) {
			// Potentially inherited from outer <beans> sections, otherwise falling back to 'no'.
			autowire = (parentDefaults != null ? parentDefaults.getAutowire() : AUTOWIRE_NO_VALUE);
		}
		defaults.setAutowire(autowire);

		// Don't fall back to parentDefaults for dependency-check as it's no longer supported in
		// <beans> as of 3.0. Therefore, no nested <beans> would ever need to fall back to it.
		defaults.setDependencyCheck(root.getAttribute(DEFAULT_DEPENDENCY_CHECK_ATTRIBUTE));

		if (root.hasAttribute(DEFAULT_AUTOWIRE_CANDIDATES_ATTRIBUTE)) {
			defaults.setAutowireCandidates(root.getAttribute(DEFAULT_AUTOWIRE_CANDIDATES_ATTRIBUTE));
		}
		else if (parentDefaults != null) {
			defaults.setAutowireCandidates(parentDefaults.getAutowireCandidates());
		}

		if (root.hasAttribute(DEFAULT_INIT_METHOD_ATTRIBUTE)) {
			defaults.setInitMethod(root.getAttribute(DEFAULT_INIT_METHOD_ATTRIBUTE));
		}
		else if (parentDefaults != null) {
			defaults.setInitMethod(parentDefaults.getInitMethod());
		}

		if (root.hasAttribute(DEFAULT_DESTROY_METHOD_ATTRIBUTE)) {
			defaults.setDestroyMethod(root.getAttribute(DEFAULT_DESTROY_METHOD_ATTRIBUTE));
		}
		else if (parentDefaults != null) {
			defaults.setDestroyMethod(parentDefaults.getDestroyMethod());
		}
		//这里是？？？
		defaults.setSource(this.readerContext.extractSource(root));
	}

<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
	http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd"
	default-autowire="byName" default-lazy-init="false" default-dependency-check="all" >

public class DocumentDefaultsDefinition implements DefaultsDefinition {
	//初始化懒加载
	private String lazyInit;
	//
	private String merge;
	// 自动装载的类型 
	private String autowire;
	//
	private String dependencyCheck;

	private String autowireCandidates;
	//初始化方法
	private String initMethod;
	//销毁方法
	private String destroyMethod;
	//返回配置源对象
	private Object source;
	//省略 get set ......
}

	public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
		//获取命名空间
		String namespaceUri = getNamespaceURI(ele);
		//根据命名空间得到命名空间的处理类handler  如果是dubbo的uri 则返回的就是DubboNamespaceHandler
		//他们都继承自NamespaceHandlerSupport implements NamespaceHandler 
		//里面有调用了hander的init()...
		NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
		if (handler == null) {
			error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
			return null;
		}
		//1.根据Element的getLocalName()得到Element的name，然后根据这个name去NamespaceHandlerSupport中的一个属性为private final Map<String, BeanDefinitionParser> parsers ;中查找对应的解析器；这个解析器是什么时候被放到这个map里面的呢？TODO...
		//2.根据对应的解析器调用  .parse(element,parserContext)进行解析	
		return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
	}

public class XmlReaderContext extends ReaderContext {
	//可以看到 方法权限是private 的
	private final XmlBeanDefinitionReader reader;
	private final NamespaceHandlerResolver namespaceHandlerResolver;
	public XmlReaderContext(
			Resource resource, ProblemReporter problemReporter,
			ReaderEventListener eventListener, SourceExtractor sourceExtractor,
			XmlBeanDefinitionReader reader, NamespaceHandlerResolver namespaceHandlerResolver) {

		super(resource, problemReporter, eventListener, sourceExtractor);
		this.reader = reader;
		this.namespaceHandlerResolver = namespaceHandlerResolver;
	}
	//但是提供了一些访问的方法
	public final XmlBeanDefinitionReader getReader() {
		return this.reader;
	}
	public final BeanDefinitionRegistry getRegistry() {
		return this.reader.getRegistry();
	}
	public final ResourceLoader getResourceLoader() {
		return this.reader.getResourceLoader();
	}
	public final ClassLoader getBeanClassLoader() {
		return this.reader.getBeanClassLoader();
	}
	public final Environment getEnvironment() {
		return this.reader.getEnvironment();
	}
	public final NamespaceHandlerResolver getNamespaceHandlerResolver() {
		return this.namespaceHandlerResolver;
	}
		public String generateBeanName(BeanDefinition beanDefinition) {
		return this.reader.getBeanNameGenerator().generateBeanName(beanDefinition, getRegistry());
	}
	public String registerWithGeneratedName(BeanDefinition beanDefinition) {
		String generatedName = generateBeanName(beanDefinition);
		getRegistry().registerBeanDefinition(generatedName, beanDefinition);
		return generatedName;
	}
	public Document readDocumentFromString(String documentContent) {
		InputSource is = new InputSource(new StringReader(documentContent));
		try {
			return this.reader.doLoadDocument(is, getResource());
		}
		catch (Exception ex) {
			throw new BeanDefinitionStoreException("Failed to read XML document", ex);
		}
	}

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
		int countBefore = getRegistry().getBeanDefinitionCount();
		//创建XmlReaderContext，然后赋值给BeanDefinitionDocumentReader中readerContext属性中
		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
		return getRegistry().getBeanDefinitionCount() - countBefore;
	}
public XmlReaderContext createReaderContext(Resource resource) {
		//this 最后就是 XmlReaderContext中的XmlBeanDefinitionReader属性
		return new XmlReaderContext(resource, this.problemReporter, this.eventListener,
				this.sourceExtractor, this, getNamespaceHandlerResolver());
	}
	public NamespaceHandlerResolver getNamespaceHandlerResolver() {
		if (this.namespaceHandlerResolver == null) {
			this.namespaceHandlerResolver = createDefaultNamespaceHandlerResolver();
		}
		return this.namespaceHandlerResolver;
	}
	
	protected NamespaceHandlerResolver createDefaultNamespaceHandlerResolver() {
		return new DefaultNamespaceHandlerResolver(getResourceLoader().getClassLoader());
	}

protected void doRegisterBeanDefinitions(Element root) {
		BeanDefinitionParserDelegate parent = this.delegate;
		this.delegate = createDelegate(getReaderContext(), root, parent); 
		//省略.....
		}