預設標籤解析

概述：本節重點詳細分析預設標籤的解析過程。接上一篇文章講到parseBeanDefinitions(root, delegate);

/**
	 * Parse the elements at the root level in the document:
	 * "import", "alias", "bean".
	 * @param root the DOM root element of the document
	 */
	protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
		if (delegate.isDefaultNamespace(root.getNamespaceURI())) {
			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 = ele.getNamespaceURI();
					if (delegate.isDefaultNamespace(namespaceUri)) {
						parseDefaultElement(ele, delegate);
					}
					else {
						delegate.parseCustomElement(ele);
					}
				}
			}
		}
		else {
			delegate.parseCustomElement(root);
		}
	}
 

在Spring的XMl配置裡面有兩個Bean宣告，一個是預設的<bean id="test"  class="">，一個是<tx:annotation-driven>，兩種方式的解析差異非常大。本節討論預設解析。。。（parseDefaultElement(ele, delegate）。。。

預設標籤的解析在函式parseDefaultElement(ele, delegate)中進行，分別對4種不同的標籤（import,alias,bean和beans）做了不同處理。原始碼如下：

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);
		}
		else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
			// recurse
			doRegisterBeanDefinitions(ele);
		}
	}

/**
	 * Process the given bean element, parsing the bean definition
	 * and registering it with the registry.
	 */
	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));
		}
	}
 

一、首先委託BeanDefinitionDelegate類的parseBeanDefinitionElement方法進行元素的解析，返回BeanDefinitionHolder型別的例項bdHolder，經過這個方法後bdHolder例項已經包含了我們配置檔案中的各種屬性了，例如class，name，id，alias等。 

/**
	 * Parses the supplied {@code <bean>} element. May return {@code null}
	 * if there were errors during parse. Errors are reported to the
	 * {@link org.springframework.beans.factory.parsing.ProblemReporter}.
	 */
	public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) {
		return parseBeanDefinitionElement(ele, null);
	}

	/**
	 * Parses the supplied {@code <bean>} element. May return {@code null}
	 * if there were errors during parse. Errors are reported to the
	 * {@link org.springframework.beans.factory.parsing.ProblemReporter}.
	 */
	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, MULTI_VALUE_ATTRIBUTE_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;
	}
 

分4步完成：

--提取元素中的id和name屬性 
--步解析其他所有屬性並統一封裝到GenericBeanDefinition型別的例項中 

	/**
	 * Parse the bean definition itself, without regard to name or aliases. May return
	 * {@code null} if problems occurred during the parsing of the bean definition.
	 */
	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;
	}

至此，class屬性、parent屬性，解析元素，解析lookup-method屬性，解析replace-method屬性，解析建構函式的引數，解析properties子元素，解析qualifier子元素等已經看到了，下面就是一些複雜標籤的解析了。

其中，建立用於屬性承載的BeanDefinition

AbstractBeanDefinition bd = createBeanDefinition(className, parent);

BeanDefinition是一個介面，在spring中此介面有三種實現：RootBeanDefinition、ChildBeanDefinition已經GenericBeanDefinition。而三種實現都繼承了AbstractBeanDefinition，其中BeanDefinition是配置檔案元素標籤在容器中的內部表示形式。元素標籤擁有class、scope、lazy-init等屬性，BeanDefinition則提供了相應的beanClass、scope、lazyInit屬性，BeanDefinition和中的屬性一一對應。

其中RootBeanDefinition是最常用的實現類，他對應一般性的元素標籤，

GenericBeanDefinition是自2.5版本以後新加入的bean檔案配置屬性定義類，是一站式服務的。 
在配置檔案中可以定義父和子，父用RootBeanDefinition表示，而子用ChildBeanDefinition表示，而沒有父的就使用RootBeanDefinition表示。AbstractBeanDefinition對兩者共同的類資訊進行抽象。Spring通過BeanDefinition將配置檔案中的配置資訊轉換為容器的內部表示，並將這些BeanDefinition註冊到BeanDefinitionRegistry中。Spring容器的BeanDefinitionRegistry就像是Spring配置資訊的記憶體資料庫，主要是以map的形式儲存，後續操作直接從BeanDefinitionResistry中讀取配置資訊。程式碼如下：

/**
	 * Create a bean definition for the given class name and parent name.
	 * @param className the name of the bean class
	 * @param parentName the name of the bean's parent bean
	 * @return the newly created bean definition
	 * @throws ClassNotFoundException if bean class resolution was attempted but failed
	 */
	protected AbstractBeanDefinition createBeanDefinition(String className, String parentName)
			throws ClassNotFoundException {

		return BeanDefinitionReaderUtils.createBeanDefinition(
				parentName, className, this.readerContext.getBeanClassLoader());
	}

/**
	 * Create a new GenericBeanDefinition for the given parent name and class name,
	 * eagerly loading the bean class if a ClassLoader has been specified.
	 * @param parentName the name of the parent bean, if any
	 * @param className the name of the bean class, if any
	 * @param classLoader the ClassLoader to use for loading bean classes
	 * (can be {@code null} to just register bean classes by name)
	 * @return the bean definition
	 * @throws ClassNotFoundException if the bean class could not be loaded
	 */
	public static AbstractBeanDefinition createBeanDefinition(
			String parentName, String className, ClassLoader classLoader) throws ClassNotFoundException {

		GenericBeanDefinition bd = new GenericBeanDefinition();
		bd.setParentName(parentName);
		if (className != null) {
			if (classLoader != null) {
				bd.setBeanClass(ClassUtils.forName(className, classLoader));
			}
			else {
				bd.setBeanClassName(className);
			}
		}
		return bd;
	}

--如果檢測到bean沒有指定beanName，那麼使用預設規則為此bean生成beanName。 
--將獲取到的資訊封裝到BeanDefinitionHolder的例項中。 

（2）當返回的dbHolder不為空的情況下若存在預設標籤的子節點下再有自定義屬性，還需要再次對自定義標籤進行解析。 
（3）當解析完成後，需要對解析後的bdHolder進行註冊，註冊過程委託給了BeanDefinitionReaderUtils的registerBeanDefinition方法。 
（4）最後發出響應事件，通知相關的監聽器已經載入完這個Bean了。

下面分析解析各種屬性：當建立好了承載bean資訊的例項後，接下來就是解析各種屬性了，首先我們看下parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);方法，程式碼如下：

/**
	 * Apply the attributes of the given bean element to the given bean * definition.
	 * @param ele bean declaration element
	 * @param beanName bean name
	 * @param containingBean containing bean definition
	 * @return a bean definition initialized according to the bean element attributes
	 */
	public AbstractBeanDefinition parseBeanDefinitionAttributes(Element ele, String beanName,
			BeanDefinition containingBean, AbstractBeanDefinition bd) {

		if (ele.hasAttribute(SINGLETON_ATTRIBUTE)) {
			error("Old 1.x 'singleton' attribute in use - upgrade to 'scope' declaration", ele);
		}
		else if (ele.hasAttribute(SCOPE_ATTRIBUTE)) {
			bd.setScope(ele.getAttribute(SCOPE_ATTRIBUTE));
		}
		else if (containingBean != null) {
			// Take default from containing bean in case of an inner bean definition.
			bd.setScope(containingBean.getScope());
		}

		if (ele.hasAttribute(ABSTRACT_ATTRIBUTE)) {
			bd.setAbstract(TRUE_VALUE.equals(ele.getAttribute(ABSTRACT_ATTRIBUTE)));
		}

		String lazyInit = ele.getAttribute(LAZY_INIT_ATTRIBUTE);
		if (DEFAULT_VALUE.equals(lazyInit)) {
			lazyInit = this.defaults.getLazyInit();
		}
		bd.setLazyInit(TRUE_VALUE.equals(lazyInit));

		String autowire = ele.getAttribute(AUTOWIRE_ATTRIBUTE);
		bd.setAutowireMode(getAutowireMode(autowire));

		String dependencyCheck = ele.getAttribute(DEPENDENCY_CHECK_ATTRIBUTE);
		bd.setDependencyCheck(getDependencyCheck(dependencyCheck));

		if (ele.hasAttribute(DEPENDS_ON_ATTRIBUTE)) {
			String dependsOn = ele.getAttribute(DEPENDS_ON_ATTRIBUTE);
			bd.setDependsOn(StringUtils.tokenizeToStringArray(dependsOn, MULTI_VALUE_ATTRIBUTE_DELIMITERS));
		}

		String autowireCandidate = ele.getAttribute(AUTOWIRE_CANDIDATE_ATTRIBUTE);
		if ("".equals(autowireCandidate) || DEFAULT_VALUE.equals(autowireCandidate)) {
			String candidatePattern = this.defaults.getAutowireCandidates();
			if (candidatePattern != null) {
				String[] patterns = StringUtils.commaDelimitedListToStringArray(candidatePattern);
				bd.setAutowireCandidate(PatternMatchUtils.simpleMatch(patterns, beanName));
			}
		}
		else {
			bd.setAutowireCandidate(TRUE_VALUE.equals(autowireCandidate));
		}

		if (ele.hasAttribute(PRIMARY_ATTRIBUTE)) {
			bd.setPrimary(TRUE_VALUE.equals(ele.getAttribute(PRIMARY_ATTRIBUTE)));
		}

		if (ele.hasAttribute(INIT_METHOD_ATTRIBUTE)) {
			String initMethodName = ele.getAttribute(INIT_METHOD_ATTRIBUTE);
			if (!"".equals(initMethodName)) {
				bd.setInitMethodName(initMethodName);
			}
		}
		else {
			if (this.defaults.getInitMethod() != null) {
				bd.setInitMethodName(this.defaults.getInitMethod());
				bd.setEnforceInitMethod(false);
			}
		}

		if (ele.hasAttribute(DESTROY_METHOD_ATTRIBUTE)) {
			String destroyMethodName = ele.getAttribute(DESTROY_METHOD_ATTRIBUTE);
			if (!"".equals(destroyMethodName)) {
				bd.setDestroyMethodName(destroyMethodName);
			}
		}
		else {
			if (this.defaults.getDestroyMethod() != null) {
				bd.setDestroyMethodName(this.defaults.getDestroyMethod());
				bd.setEnforceDestroyMethod(false);
			}
		}

		if (ele.hasAttribute(FACTORY_METHOD_ATTRIBUTE)) {
			bd.setFactoryMethodName(ele.getAttribute(FACTORY_METHOD_ATTRIBUTE));
		}
		if (ele.hasAttribute(FACTORY_BEAN_ATTRIBUTE)) {
			bd.setFactoryBeanName(ele.getAttribute(FACTORY_BEAN_ATTRIBUTE));
		}

		return bd;
	}

可以看到Spring完成了對所有bean屬性的解析，包括：解析singleton屬性、解析scope屬性、解析abstract屬性、解析lazy_init屬性、解析autowire屬性、解析dependsOn屬性、解析autowireCandidate屬性、解析primary屬性、解析init_method屬性、解析destroy_method屬性、解析factory_method屬性、析factory_bean屬性。

解析子元素meta屬性（parseMetaElements(ele, bd);）

public void parseMetaElements(Element ele, BeanMetadataAttributeAccessor attributeAccessor) {
		NodeList nl = ele.getChildNodes();
		for (int i = 0; i < nl.getLength(); i++) {
			Node node = nl.item(i);
			if (isCandidateElement(node) && nodeNameEquals(node, META_ELEMENT)) {
				Element metaElement = (Element) node;
				String key = metaElement.getAttribute(KEY_ATTRIBUTE);
				String value = metaElement.getAttribute(VALUE_ATTRIBUTE);
				BeanMetadataAttribute attribute = new BeanMetadataAttribute(key, value);
				attribute.setSource(extractSource(metaElement));
				attributeAccessor.addMetadataAttribute(attribute);
			}
		}
	}

解析子元素lookup-method(),(parseLookupOverrideSubElements(ele, bd.getMethodOverrides());)

/**
	 * Parse lookup-override sub-elements of the given bean element.
	 */
	public void parseLookupOverrideSubElements(Element beanEle, MethodOverrides overrides) {
		NodeList nl = beanEle.getChildNodes();
		for (int i = 0; i < nl.getLength(); i++) {
			Node node = nl.item(i);
			if (isCandidateElement(node) && nodeNameEquals(node, LOOKUP_METHOD_ELEMENT)) {
				Element ele = (Element) node;
				String methodName = ele.getAttribute(NAME_ATTRIBUTE);
				String beanRef = ele.getAttribute(BEAN_ELEMENT);
				LookupOverride override = new LookupOverride(methodName, beanRef);
				override.setSource(extractSource(ele));
				overrides.addOverride(override);
			}
		}
	}

解析子元素replaced-method,(parseReplacedMethodSubElements(ele, bd.getMethodOverrides());)

/**
	 * Parse replaced-method sub-elements of the given bean element.
	 */
	public void parseReplacedMethodSubElements(Element beanEle, MethodOverrides overrides) {
		NodeList nl = beanEle.getChildNodes();
		for (int i = 0; i < nl.getLength(); i++) {
			Node node = nl.item(i);
			if (isCandidateElement(node) && nodeNameEquals(node, REPLACED_METHOD_ELEMENT)) {
				Element replacedMethodEle = (Element) node;
				String name = replacedMethodEle.getAttribute(NAME_ATTRIBUTE);
				String callback = replacedMethodEle.getAttribute(REPLACER_ATTRIBUTE);
				ReplaceOverride replaceOverride = new ReplaceOverride(name, callback);
				// Look for arg-type match elements.
				List<Element> argTypeEles = DomUtils.getChildElementsByTagName(replacedMethodEle, ARG_TYPE_ELEMENT);
				for (Element argTypeEle : argTypeEles) {
					String match = argTypeEle.getAttribute(ARG_TYPE_MATCH_ATTRIBUTE);
					match = (StringUtils.hasText(match) ? match : DomUtils.getTextValue(argTypeEle));
					if (StringUtils.hasText(match)) {
						replaceOverride.addTypeIdentifier(match);
					}
				}
				replaceOverride.setSource(extractSource(replacedMethodEle));
				overrides.addOverride(replaceOverride);
			}
		}
	}

解析子元素constructor-arg,(parseConstructorArgElements(ele, bd);)

/**
	 * Parse constructor-arg sub-elements of the given bean element.
	 */
	public void parseConstructorArgElements(Element beanEle, BeanDefinition bd) {
		NodeList nl = beanEle.getChildNodes();
		for (int i = 0; i < nl.getLength(); i++) {
			Node node = nl.item(i);
			if (isCandidateElement(node) && nodeNameEquals(node, CONSTRUCTOR_ARG_ELEMENT)) {
				parseConstructorArgElement((Element) node, bd);
			}
		}
	}

/**
	 * Parse a constructor-arg element.
	 */
	public void parseConstructorArgElement(Element ele, BeanDefinition bd) {
		String indexAttr = ele.getAttribute(INDEX_ATTRIBUTE);
		String typeAttr = ele.getAttribute(TYPE_ATTRIBUTE);
		String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
		if (StringUtils.hasLength(indexAttr)) {
			try {
				int index = Integer.parseInt(indexAttr);
				if (index < 0) {
					error("'index' cannot be lower than 0", ele);
				}
				else {
					try {
						this.parseState.push(new ConstructorArgumentEntry(index));
						Object value = parsePropertyValue(ele, bd, null);
						ConstructorArgumentValues.ValueHolder valueHolder = new ConstructorArgumentValues.ValueHolder(value);
						if (StringUtils.hasLength(typeAttr)) {
							valueHolder.setType(typeAttr);
						}
						if (StringUtils.hasLength(nameAttr)) {
							valueHolder.setName(nameAttr);
						}
						valueHolder.setSource(extractSource(ele));
						if (bd.getConstructorArgumentValues().hasIndexedArgumentValue(index)) {
							error("Ambiguous constructor-arg entries for index " + index, ele);
						}
						else {
							bd.getConstructorArgumentValues().addIndexedArgumentValue(index, valueHolder);
						}
					}
					finally {
						this.parseState.pop();
					}
				}
			}
			catch (NumberFormatException ex) {
				error("Attribute 'index' of tag 'constructor-arg' must be an integer", ele);
			}
		}
		else {
			try {
				this.parseState.push(new ConstructorArgumentEntry());
				Object value = parsePropertyValue(ele, bd, null);
				ConstructorArgumentValues.ValueHolder valueHolder = new ConstructorArgumentValues.ValueHolder(value);
				if (StringUtils.hasLength(typeAttr)) {
					valueHolder.setType(typeAttr);
				}
				if (StringUtils.hasLength(nameAttr)) {
					valueHolder.setName(nameAttr);
				}
				valueHolder.setSource(extractSource(ele));
				bd.getConstructorArgumentValues().addGenericArgumentValue(valueHolder);
			}
			finally {
				this.parseState.pop();
			}
		}
	}
上述程式碼的流程可以簡單的總結為如下： 
（1）首先提取index、type、name等屬性 
（2）根據是否配置了index屬性解析流程不同 
如果配置了index屬性，解析流程如下： 
（1）使用parsePropertyValue(ele, bd, null)方法讀取constructor-arg的子元素 
（2）使用ConstructorArgumentValues.ValueHolder封裝解析出來的元素 
（3）將index、type、name屬性也封裝進ValueHolder中，然後將ValueHoder新增到當前beanDefinition的ConstructorArgumentValues的indexedArgumentValues


呼叫解析子元素的過程：
/**
	 * Get the value of a property element. May be a list etc.
	 * Also used for constructor arguments, "propertyName" being null in this case.
	 */
	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 parsePropertySubElement(Element ele, BeanDefinition bd) {
		return parsePropertySubElement(ele, bd, null);
	}

上述程式碼的執行邏輯簡單總結為： 
（1）首先略過decription和meta屬性 
（2）提取constructor-arg上的ref和value屬性，並驗證是否存在 
（3）存在ref屬性時，用RuntimeBeanReference來封裝ref 
（4）存在value屬性時，用TypedStringValue來封裝 
（5）存在子元素時，對於子元素的處理使用了方法parsePropertySubElement(subElement, bd);，

程式碼如下：


/**
	 * Parse a value, ref or collection sub-element of a property or
	 * constructor-arg element.
	 * @param ele subelement of property element; we don't know which yet
	 * @param defaultValueType the default type (class name) for any
	 * {@code &lt;value&gt;} tag that might be created
	 */
	public Object parsePropertySubElement(Element ele, BeanDefinition bd, String defaultValueType) {
		if (!isDefaultNamespace(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;
		}
	}

 解析子元素Property,(parsePropertyElements(ele, bd);)

/**
	 * Parse property sub-elements of the given bean element.
	 */
	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 (isCandidateElement(node) && nodeNameEquals(node, PROPERTY_ELEMENT)) {
				parsePropertyElement((Element) node, bd);
			}
		}
	}

解析子元素qualifier,(parseQualifierElements(ele, bd);)

/**
	 * Parse qualifier sub-elements of the given bean element.
	 */
	public void parseQualifierElements(Element beanEle, AbstractBeanDefinition bd) {
		NodeList nl = beanEle.getChildNodes();
		for (int i = 0; i < nl.getLength(); i++) {
			Node node = nl.item(i);
			if (isCandidateElement(node) && nodeNameEquals(node, QUALIFIER_ELEMENT)) {
				parseQualifierElement((Element) node, bd);
			}
		}
	}

至此，我們已經完成了從xml配置檔案到BeanDefinition的轉換，轉換後的例項是GenericBeanDefinition的例項。而GenericBeanDefinition是AbstractBeanDefinition的子類，那現在我們就先看下AbstractBeanDefinition中的屬性

/**
 * Base class for concrete, full-fledged
 * {@link org.springframework.beans.factory.config.BeanDefinition} classes,
 * factoring out common properties of {@link GenericBeanDefinition},
 * {@link RootBeanDefinition} and {@link ChildBeanDefinition}.
 *
 * <p>The autowire constants match the ones defined in the
 * {@link org.springframework.beans.factory.config.AutowireCapableBeanFactory}
 * interface.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @author Mark Fisher
 * @see RootBeanDefinition
 * @see ChildBeanDefinition
 */
@SuppressWarnings("serial")
public abstract class AbstractBeanDefinition extends BeanMetadataAttributeAccessor
		implements BeanDefinition, Cloneable {

	/**
	 * Constant for the default scope name: "", equivalent to singleton status
	 * but to be overridden from a parent bean definition (if applicable).
	 */
	public static final String SCOPE_DEFAULT = "";

	/**
	 * Constant that indicates no autowiring at all.
	 * @see #setAutowireMode
	 */
	public static final int AUTOWIRE_NO = AutowireCapableBeanFactory.AUTOWIRE_NO;

	/**
	 * Constant that indicates autowiring bean properties by name.
	 * @see #setAutowireMode
	 */
	public static final int AUTOWIRE_BY_NAME = AutowireCapableBeanFactory.AUTOWIRE_BY_NAME;

	/**
	 * Constant that indicates autowiring bean properties by type.
	 * @see #setAutowireMode
	 */
	public static final int AUTOWIRE_BY_TYPE = AutowireCapableBeanFactory.AUTOWIRE_BY_TYPE;

	/**
	 * Constant that indicates autowiring a constructor.
	 * @see #setAutowireMode
	 */
	public static final int AUTOWIRE_CONSTRUCTOR = AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR;

	/**
	 * Constant that indicates determining an appropriate autowire strategy
	 * through introspection of the bean class.
	 * @see #setAutowireMode
	 * @deprecated as of Spring 3.0: If you are using mixed autowiring strategies,
	 * use annotation-based autowiring for clearer demarcation of autowiring needs.
	 */
	@Deprecated
	public static final int AUTOWIRE_AUTODETECT = AutowireCapableBeanFactory.AUTOWIRE_AUTODETECT;

	/**
	 * Constant that indicates no dependency check at all.
	 * @see #setDependencyCheck
	 */
	public static final int DEPENDENCY_CHECK_NONE = 0;

	/**
	 * Constant that indicates dependency checking for object references.
	 * @see #setDependencyCheck
	 */
	public static final int DEPENDENCY_CHECK_OBJECTS = 1;

	/**
	 * Constant that indicates dependency checking for "simple" properties.
	 * @see #setDependencyCheck
	 * @see org.springframework.beans.BeanUtils#isSimpleProperty
	 */
	public static final int DEPENDENCY_CHECK_SIMPLE = 2;

	/**
	 * Constant that indicates dependency checking for all properties
	 * (object references as well as "simple" properties).
	 * @see #setDependencyCheck
	 */
	public static final int DEPENDENCY_CHECK_ALL = 3;

	/**
	 * Constant that indicates the container should attempt to infer the
	 * {@link #setDestroyMethodName destroy method name} for a bean as opposed to
	 * explicit specification of a method name. The value {@value} is specifically
	 * designed to include characters otherwise illegal in a method name, ensuring
	 * no possibility of collisions with legitimately named methods having the same
	 * name.
	 * <p>Currently, the method names detected during destroy method inference
	 * are "close" and "shutdown", if present on the specific bean class.
	 */
	public static final String INFER_METHOD = "(inferred)";


	private volatile Object beanClass;

	private String scope = SCOPE_DEFAULT;

	private boolean abstractFlag = false;

	private boolean lazyInit = false;

	private int autowireMode = AUTOWIRE_NO;

	private int dependencyCheck = DEPENDENCY_CHECK_NONE;

	private String[] dependsOn;

	private boolean autowireCandidate = true;

	private boolean primary = false;

	private final Map<String, AutowireCandidateQualifier> qualifiers =
			new LinkedHashMap<String, AutowireCandidateQualifier>(0);

	private boolean nonPublicAccessAllowed = true;

	private boolean lenientConstructorResolution = true;

	private ConstructorArgumentValues constructorArgumentValues;

	private MutablePropertyValues propertyValues;

	private MethodOverrides methodOverrides = new MethodOverrides();

	private String factoryBeanName;

	private String factoryMethodName;

	private String initMethodName;

	private String destroyMethodName;

	private boolean enforceInitMethod = true;

	private boolean enforceDestroyMethod = true;

	private boolean synthetic = false;

	private int role = BeanDefinition.ROLE_APPLICATION;

	private String description;

	private Resource resource;


	/**
	 * Create a new AbstractBeanDefinition with default settings.
	 */
	protected AbstractBeanDefinition() {
		this(null, null);
	}

 再說一下解析預設標籤中的自定義標籤元素。

至此，我們已經完成了分析預設標籤的解析與提取的過程，回顧一下起始函式。我們已經用了很多篇幅描述BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);接下來我們進行BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);程式碼的分析，作用就是對BeanDefinition進行裝飾。

/**
	 * Process the given bean element, parsing the bean definition
	 * and registering it with the registry.
	 */
	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));
		}
	}

    bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);

	public BeanDefinitionHolder decorateBeanDefinitionIfRequired(Element ele, BeanDefinitionHolder definitionHolder) {
		return decorateBeanDefinitionIfRequired(ele, definitionHolder, null);
	}
public BeanDefinitionHolder decorateBeanDefinitionIfRequired(
			Element ele, BeanDefinitionHolder definitionHolder, BeanDefinition containingBd) {

		BeanDefinitionHolder finalDefinition = definitionHolder;

		// Decorate based on custom attributes first.
		NamedNodeMap attributes = ele.getAttributes();
		for (int i = 0; i < attributes.getLength(); i++) {
			Node node = attributes.item(i);
			finalDefinition = decorateIfRequired(node, finalDefinition, containingBd);
		}

		// Decorate based on custom nested elements.
		NodeList children = ele.getChildNodes();
		for (int i = 0; i < children.getLength(); i++) {
			Node node = children.item(i);
			if (node.getNodeType() == Node.ELEMENT_NODE) {
				finalDefinition = decorateIfRequired(node, finalDefinition, containingBd);
			}
		}
		return finalDefinition;
	}

上述程式碼，分別對所有元素的屬性以及子節點進行了decorateIfRequired函式的呼叫。

public BeanDefinitionHolder decorateIfRequired(
			Node node, BeanDefinitionHolder originalDef, BeanDefinition containingBd) {

		String namespaceUri = getNamespaceURI(node);
		if (!isDefaultNamespace(namespaceUri)) {
			NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
			if (handler != null) {
				return handler.decorate(node, originalDef, new ParserContext(this.readerContext, this, containingBd));
			}
			else if (namespaceUri != null && namespaceUri.startsWith("http://www.springframework.org/")) {
				error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", node);
			}
			else {
				// A custom namespace, not to be handled by Spring - maybe "xml:...".
				if (logger.isDebugEnabled()) {
					logger.debug("No Spring NamespaceHandler found for XML schema namespace [" + namespaceUri + "]");
				}
			}
		}
		return originalDef;
	}

程式走到這裡已經很清楚了，首先獲得元素的屬性或者名稱空間，以確定該元素或者屬性是否適合於自定義標籤的解析條件，找出自定義型別所對應的NamespaceHandler並進行進一步解析。

最後就是註冊解析。

對於配置檔案解析和裝飾都完成了，唯一還剩下一步就是processBeanDefinition函式中、BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());

/**
	 * Register the given bean definition with the given bean factory.
	 * @param definitionHolder the bean definition including name and aliases
	 * @param registry the bean factory to register with
	 * @throws BeanDefinitionStoreException if registration failed
	 */
	public static void registerBeanDefinition(
			BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
			throws BeanDefinitionStoreException {

		// Register bean definition under primary name.
使用beanName做唯一的標識
		String beanName = definitionHolder.getBeanName();
		registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

		// Register aliases for bean name, if any.
		String[] aliases = definitionHolder.getAliases();
		if (aliases != null) {
			for (String aliase : aliases) {
				registry.registerAlias(beanName, aliase);
			}
		}
	}

從上面的程式碼可以看出，解析的beanDefinition被註冊到BeanDefinitionRegistry型別的例項registry中，而對於beanDefinition的註冊分成了兩部分：通過beanName的註冊和通過別名的註冊。

1.通過beanName的註冊、registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

//---------------------------------------------------------------------
	// Implementation of BeanDefinitionRegistry interface
	//---------------------------------------------------------------------

	@Override
	public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
			throws BeanDefinitionStoreException {

		Assert.hasText(beanName, "Bean name must not be empty");
		Assert.notNull(beanDefinition, "BeanDefinition must not be null");

		if (beanDefinition instanceof AbstractBeanDefinition) {
			try {
註冊前的最後一次校驗，這裡的校驗不同於之前的XML的校驗
主要是針對AbstractBeanDefinition屬性中的methodOverrides校驗
校驗methodOverrides是否與工廠方法並存或者methodOverrides對應的方法根本不存在。
				((AbstractBeanDefinition) beanDefinition).validate();
			}
			catch (BeanDefinitionValidationException ex) {
				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Validation of bean definition failed", ex);
			}
		}

		BeanDefinition oldBeanDefinition;

		oldBeanDefinition = this.beanDefinitionMap.get(beanName);
		if (oldBeanDefinition != null) {
			if (!this.allowBeanDefinitionOverriding) {
				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
						"': There is already [" + oldBeanDefinition + "] bound.");
			}
			else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
				// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
				if (this.logger.isWarnEnabled()) {
					this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +
							" with a framework-generated bean definition ': replacing [" +
							oldBeanDefinition + "] with [" + beanDefinition + "]");
				}
			}
			else {
				if (this.logger.isInfoEnabled()) {
					this.logger.info("Overriding bean definition for bean '" + beanName +
							"': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
				}
			}
		}
		else {
beanName的記錄
			this.beanDefinitionNames.add(beanName);
			this.manualSingletonNames.remove(beanName);
			this.frozenBeanDefinitionNames = null;
		}
beanDefinition的註冊
		this.beanDefinitionMap.put(beanName, beanDefinition);

		if (oldBeanDefinition != null || containsSingleton(beanName)) {
		重置所有的beanName快取
          resetBeanDefinition(beanName);
		}
	}

綜上分析上面程式碼我們簡單總結下對於beanDefinition的註冊的處理步驟： 
（1）對AbstractBeanDefinition的校驗，在解析XML檔案的時候我們提過校驗，但是此校驗非彼校驗，之前的校驗是針對於XML格式的校驗，而此時的校驗是針對AbstractBeanDefinition的methodOverrides屬性的。 
（2）對beanName已經註冊的情況的處理，如果設定了不允許bean的覆蓋，則需要丟擲異常，否陳直接覆蓋 
（3）加入map快取 
（4）清除解析之前留下的對應beanName的快取

2.通過別名註冊BeanDefinition、registry.registerAlias(beanName, aliase);}

@Override
	public void registerAlias(String name, String alias) {
		Assert.hasText(name, "'name' must not be empty");
		Assert.hasText(alias, "'alias' must not be empty");
//如果beanName與alias相同的，不記錄alias，並刪除對應的alias
		if (alias.equals(name)) {
			this.aliasMap.remove(alias);
		}
		else {
//如果alias不允許被覆蓋則丟擲異常
			if (!allowAliasOverriding()) {
				String registeredName = this.aliasMap.get(alias);
				if (registeredName != null && !registeredName.equals(name)) {
					throw new IllegalStateException("Cannot register alias '" + alias + "' for name '" +
							name + "': It is already registered for name '" + registeredName + "'.");
				}
			}
//核查迴圈異常
			checkForAliasCircle(name, alias);
			this.aliasMap.put(alias, name);
		}

綜上述程式碼的流程總結如下： 
（1）alias與beanName相同情況處理，
（2）alias覆蓋處理。
（3）alias迴圈檢查，

最終，通知監聽器解析及註冊工作已完成、getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));這裡的實現只為了擴充套件，當開發人員需要對註冊的BeanDefinition事件進行監聽的方式並將處理邏輯寫入監聽器中。

二、alias標籤的解析

else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
			processAliasRegistration(ele);
		}

/**
	 * Process the given alias element, registering the alias with the registry.
	 */
	protected void processAliasRegistration(Element ele) {
//beanName獲取

		String name = ele.getAttribute(NAME_ATTRIBUTE);
//alias獲取
		String alias = ele.getAttribute(ALIAS_ATTRIBUTE);
		boolean valid = true;
		if (!StringUtils.hasText(name)) {
			getReaderContext().error("Name must not be empty", ele);
			valid = false;
		}
		if (!StringUtils.hasText(alias)) {
			getReaderContext().error("Alias must not be empty", ele);
			valid = false;
		}
		if (valid) {
			try {
//註冊alias
				getReaderContext().getRegistry().registerAlias(name, alias);
			}
			catch (Exception ex) {
				getReaderContext().error("Failed to register alias '" + alias +
						"' for bean with name '" + name + "'", ele, ex);
			}
//註冊別名後通知監聽器做相應的處理
			getReaderContext().fireAliasRegistered(name, alias, extractSource(ele));
		}
	}

三、import標籤的解析

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
		if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
			importBeanDefinitionResource(ele);
		}

/**
	 * Parse an "import" element and load the bean definitions
	 * from the given resource into the bean factory.
	 */
	protected void importBeanDefinitionResource(Element ele) {
		String location = ele.getAttribute(RESOURCE_ATTRIBUTE);
		if (!StringUtils.hasText(location)) {
			getReaderContext().error("Resource location must not be empty", ele);
			return;
		}

		// Resolve system properties: e.g. "${user.dir}"
		location = getReaderContext().getEnvironment().resolveRequiredPlaceholders(location);

		Set<Resource> actualResources = new LinkedHashSet<Resource>(4);

		// Discover whether the location is an absolute or relative URI
		boolean absoluteLocation = false;
		try {
			absoluteLocation = ResourcePatternUtils.isUrl(location) || ResourceUtils.toURI(location).isAbsolute();
		}
		catch (URISyntaxException ex) {
			// cannot convert to an URI, considering the location relative
			// unless it is the well-known Spring prefix "classpath*:"
		}

		// Absolute or relative?
		if (absoluteLocation) {
			try {
				int importCount = getReaderContext().getReader().loadBeanDefinitions(location, actualResources);
				if (logger.isDebugEnabled()) {
					logger.debug("Imported " + importCount + " bean definitions from URL location [" + location + "]");
				}
			}
			catch (BeanDefinitionStoreException ex) {
				getReaderContext().error(
						"Failed to import bean definitions from URL location [" + location + "]", ele, ex);
			}
		}
		else {
			// No URL -> considering resource location as relative to the current file.
			try {
				int importCount;
				Resource relativeResource = getReaderContext().getResource().createRelative(location);
				if (relativeResource.exists()) {
					importCount = getReaderContext().getReader().loadBeanDefinitions(relativeResource);
					actualResources.add(relativeResource);
				}
				else {
					String baseLocation = getReaderContext().getResource().getURL().toString();
					importCount = getReaderContext().getReader().loadBeanDefinitions(
							StringUtils.applyRelativePath(baseLocation, location), actualResources);
				}
				if (logger.isDebugEnabled()) {
					logger.debug("Imported " + importCount + " bean definitions from relative location [" + location + "]");
				}
			}
			catch (IOException ex) {
				getReaderContext().error("Failed to resolve current resource location", ele, ex);
			}
			catch (BeanDefinitionStoreException ex) {
				getReaderContext().error("Failed to import bean definitions from relative location [" + location + "]",
						ele, ex);
			}
		}
		Resource[] actResArray = actualResources.toArray(new Resource[actualResources.size()]);
		getReaderContext().fireImportProcessed(location, actResArray, extractSource(ele));
	}

方法的主要工作如下： 
（1）獲取resource屬性所表示的路徑 
（2）解析路徑中的系統屬性 
（3）判斷location是絕對路徑還是相對路徑 
（4）如果是絕對路徑則遞迴呼叫bean的解析過程，進行另一次解析 
（5）如果是相對路徑則計算出絕對路徑進行解析 
（6）通知監聽器，解析完成
至此，預設標籤解析結束。。。