Srping原始碼之XMLBeanFactory

​ 本文是針對Srping的XMLBeanFactory來進行解析xml並將解析後的資訊使用GenericBeanDefinition作為載體進行註冊,xmlBeanFactory已經在Spring 3.1中被標記為不建議使用，但是我們分析原始碼不影響，因為原始碼並未改變，並ApplicationContext依舊使用XmlBeanDefinitionReader和DefaultListableBeanFactory進行xml的解析和註冊工作，本篇部落格是跟原始碼一步步看spring怎麼實現bean的註冊，原始碼為spring5.X,原始碼已經在每一行上加了註釋，方便讀者學習。

GitHub: https://github.com/lantaoGitHub/spring-framework.git

• 首先我們從XMLBeanFactory入手,直接上程式碼：

package org.springframework.lantao;

import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.ClassPathResource;

public class XmlBeanFactoryTest {

    public static void main(String[] args) {
        // 資源載入
        ClassPathResource classPathResource = new ClassPathResource("spring-bean.xml");
        // XmlBeanFactory 載入資源並解析註冊bean
        BeanFactory beanFactory = new XmlBeanFactory(classPathResource);
        // BeanFactory.getBean();
        UserBean userBean = (UserBean) beanFactory.getBean("userBean");
        System.out.println(userBean.getName());
	}
}

• XmlBeanFactory解析Xml是使用了XmlBeanDefinitionReader.loadBeanDefinition()方法,原始碼如下：

@Deprecated
@SuppressWarnings({"serial", "all"})
public class XmlBeanFactory extends DefaultListableBeanFactory {

	private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this);


	/**
	 * Create a new XmlBeanFactory with the given resource,
	 * which must be parsable using DOM.
	 * @param resource the XML resource to load bean definitions from
	 * @throws BeansException in case of loading or parsing errors
	 */
	public XmlBeanFactory(Resource resource) throws BeansException {
		//呼叫構造方法  79行
		this(resource, null);
	}

	/**
	 * Create a new XmlBeanFactory with the given input stream,
	 * which must be parsable using DOM.
	 * @param resource the XML resource to load bean definitions from
	 * @param parentBeanFactory parent bean factory
	 * @throws BeansException in case of loading or parsing errors
	 */
	public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
		//ignoreDependencyInterface 忽略自動裝配
		//主要功能就是當有忽略的介面類，自動裝配會忽略這部分類的初始化裝配，因為某種情況下，此時的介面實現類不能初始化，列如BeanNameAware,要想裝配這個介面的實現物件，可以實現這個介面。
		super(parentBeanFactory);
		//這段程式碼是真正的資源載入
		this.reader.loadBeanDefinitions(resource);
	}

}

• 我們直接看loadBeanDefinition方法，原始碼：

/**
 * Load bean definitions from the specified XML file.
 * @param resource the resource descriptor for the XML file
 * @return the number of bean definitions found
 * @throws BeanDefinitionStoreException in case of loading or parsing errors
 */
@Override
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
	// 對EncodedResource進行封裝，設定String encoding, Charset charset
	return loadBeanDefinitions(new EncodedResource(resource));
}

/**
 * Load bean definitions from the specified XML file.
 * @param encodedResource the resource descriptor for the XML file,
 * allowing to specify an encoding to use for parsing the file
 * @return the number of bean definitions found
 * @throws BeanDefinitionStoreException in case of loading or parsing errors
 */
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
	//encodedResource 不可以為空
	Assert.notNull(encodedResource, "EncodedResource must not be null");
	if (logger.isTraceEnabled()) {
		logger.trace("Loading XML bean definitions from " + encodedResource);
	}

	// 通過屬性來記錄已經載入的資源
	Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
	if (currentResources == null) {
		currentResources = new HashSet<>(4);
		this.resourcesCurrentlyBeingLoaded.set(currentResources);
	}
	if (!currentResources.add(encodedResource)) {
		throw new BeanDefinitionStoreException(
				"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
	}
	try {
		// 從encodedResource已經封裝的Resource獲取InputStream
		InputStream inputStream = encodedResource.getResource().getInputStream();
		try {
			//InputSource 並不是spring的，而是 org.xml.sax
			InputSource inputSource = new InputSource(inputStream);
			//如果encodedResource 中的 Encoding 不是 null 則同步設定 InputSource的 Encoding
			if (encodedResource.getEncoding() != null) {
				inputSource.setEncoding(encodedResource.getEncoding());
			}
			//載入bean的Definitions 將xml中的資訊載入到Definition中，並且在記憶體中註冊的也是key+definitions
			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.remove();
		}
	}
}

上述原始碼可能看著比較長,但實際上這裡並不是真正解析的地方，在這裡做了如下：

1:從encodedResource已經封裝的Resource獲取InputStream；

2:如果encodedResource 中的 Encoding 不是 null 則同步設定 InputSource的 Encoding；

3:將解析動作委託給doLoadBeanDefinitions實現；

• 接下來我們繼續看doLoadBeanDefinitions方法內容：

/**
 * Actually load bean definitions from the specified XML file.
 * @param inputSource the SAX InputSource to read from
 * @param resource the resource descriptor for the XML file
 * @return the number of bean definitions found
 * @throws BeanDefinitionStoreException in case of loading or parsing errors
 * @see #doLoadDocument
 * @see #registerBeanDefinitions
 */
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
		throws BeanDefinitionStoreException {
	try {
		//載入 Document
		Document doc = doLoadDocument(inputSource, resource);
		//註冊 bean
		int count = registerBeanDefinitions(doc, resource);
		if (logger.isDebugEnabled()) {
			logger.debug("Loaded " + count + " bean definitions from " + resource);
		}
		return count;
	}
	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);
	}
}

當我們看著這個方法的時候，依舊不是真正的解析或註冊的方法，在這裡只是做了Document的載入，並將後續工作委託給了registerBeanDefinitions,registerBeanDefinitions方法的返回時註冊Bean的個數；

• 我們繼續看registerBeanDefinitions的原始碼：

/**
 * Register the bean definitions contained in the given DOM document.
 * Called by {@code loadBeanDefinitions}.
 * <p>Creates a new instance of the parser class and invokes
 * {@code registerBeanDefinitions} on it.
 * @param doc the DOM document
 * @param resource the resource descriptor (for context information)
 * @return the number of bean definitions found
 * @throws BeanDefinitionStoreException in case of parsing errors
 * @see #loadBeanDefinitions
 * @see #setDocumentReaderClass
 * @see BeanDefinitionDocumentReader#registerBeanDefinitions
 */
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
	//例項化 BeanDefinitionDocumentReader
	BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
	//獲取之前的beanDefinition載入個數
	int countBefore = getRegistry().getBeanDefinitionCount();
	//載入xml及註冊bean
	documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
	//記錄本次載入個數
	return getRegistry().getBeanDefinitionCount() - countBefore;
}

在registerBeanDefinitions方法具體實現：

1：通過BeanUtils.instantiateClass(this.documentReaderClass)的方法例項化BeanDefinitionDocumentReader；

2：通過DefaultListAbleBeanFactory中的beanDefinitionMap.size()獲取之前註冊bean的個數，（beanDefinitionMap是儲存最終的xml解析後資訊的載體，xml解析後資訊是由GenericBeanDefinition進行儲存，beanDefinitionMap的儲存格式是key:String value:GenericBeanDefinition）

3:將解析xml和註冊的工作委託給BeanDefinitionDocumentReader的registerBeanDefinitions方法；

4：記錄本次載入個數並返回；

• 繼續看BeanDefinitionDocumentReader的registerBeanDefinitions方法：

/**
 * This implementation parses bean definitions according to the "spring-beans" XSD
 * (or DTD, historically).
 * <p>Opens a DOM Document; then initializes the default settings
 * specified at the {@code <beans/>} level; then parses the contained bean definitions.
 */
@Override
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
	//例項化 ReaderContext
	this.readerContext = readerContext;
	//註冊
	doRegisterBeanDefinitions(doc.getDocumentElement());
}

• registerBeanDefinitions並沒有做什麼，我們繼續看doRegisterBeanDefinitions方法：

/**
 * Register each bean definition within the given root {@code <beans/>} element.
 */
@SuppressWarnings("deprecation")  // for Environment.acceptsProfiles(String...)
protected void doRegisterBeanDefinitions(Element root) {
	// Any nested <beans> elements will cause recursion in this method. In
	// order to propagate and preserve <beans> default-* attributes correctly,
	// keep track of the current (parent) delegate, which may be null. Create
	// the new (child) delegate with a reference to the parent for fallback purposes,
	// then ultimately reset this.delegate back to its original (parent) reference.
	// this behavior emulates a stack of delegates without actually necessitating one.
	BeanDefinitionParserDelegate parent = this.delegate;
	this.delegate = createDelegate(getReaderContext(), root, parent);

	//驗證xml namespace, BeanDefinitionParserDelegate.BEANS_NAMESPACE_URI
	if (this.delegate.isDefaultNamespace(root)) {
		//獲取Attribute
		String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
		if (StringUtils.hasText(profileSpec)) {
			String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
					profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
			// We cannot use Profiles.of(...) since profile expressions are not supported
			// in XML config. See SPR-12458 for details.
			if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
				if (logger.isDebugEnabled()) {
					logger.debug("Skipped XML bean definition file due to specified profiles [" + profileSpec +
							"] not matching: " + getReaderContext().getResource());
				}
				return;
			}
		}
	}

	//解析前處理， 內容null 留個子類實現
	preProcessXml(root);
	//解析
	parseBeanDefinitions(root, this.delegate);
	//解析後處理， 內容null 留個子類實現
	postProcessXml(root);

	this.delegate = parent;
}

在doRegisterBeanDefinitions方法中驗證xml的namespace,最重要的方法是parseBeanDefinitions，parseBeanDefinitions方法進行了解析操作；

• parseBeanDefinitions方法的原始碼：

/**
 * 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) {
	//驗證xml namespace, BeanDefinitionParserDelegate.BEANS_NAMESPACE_URI
	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)) {
					//對預設標籤處理
					parseDefaultElement(ele, delegate);
				}
				else {
					//對自定義標籤處理
					delegate.parseCustomElement(ele);
				}
			}
		}
	}
	else {
		//對自定義標籤處理
		delegate.parseCustomElement(root);
	}
}

parseBeanDefinitions方法中已經開始對標籤進行解析，區分預設標籤和自定義標籤，我們本次只對預設標籤的原始碼進行解析，自定義標籤自行DeBug，

• parseDefaultElement方法的原始碼：

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
	//解析import標籤
	if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
		importBeanDefinitionResource(ele);
	}
	//解析alias標籤並註冊
	else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
		processAliasRegistration(ele);
	}
	//解析bean標籤並註冊
	else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
		processBeanDefinition(ele, delegate);
	}
	//解析beans標籤
	else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
		// recurse
		doRegisterBeanDefinitions(ele);
	}
}

到這裡我們可以看到，spring對import/bean/alias/beans的解析過程，對於beans的解析無法就是解析beans中的bean標籤，spring直接又重新呼叫了doRegisterBeanDefinitions方法，我們接下來進行對bean標籤的解析；

• processBeanDefinition方法：

/**
 * Process the given bean element, parsing the bean definition
 * and registering it with the registry.
 */
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {

	//委託BeanDefinitionParserDelegate的parseBeanDefinitionElement方法進行元素解析並返回
	//BeanDefinitionHolder例項，BeanDefinitionHolder已經包含了配置檔案中的各種屬性

	BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
	//當BeanDefinitionHolder返回不null的情況，若存在預設標籤下的子標籤再有自定義的屬性，還需要再次解析
	if (bdHolder != null) {
		//解析預設標籤中的自定義標籤
		bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
		try {
			// Register the final decorated instance.
			// 進行例項註冊註冊操作是BeanDefinitionReaderUtisl.registerBeanDefinition進行處理
			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));
	}
}

在processBeanDefinition方法中，spring做了兩件事情：

1：委託BeanDefinitionParserDelegate的parseBeanDefinitionElement方法進行元素解析並返回BeanDefinitionHolder例項，BeanDefinitionHolder已經包含了配置檔案中的各種屬性

2：通過上獲得的BeanDefinitionHolder進行bean的註冊操作，通BeanDefinitionReaderUtils.registerBeanDefinition方法；

• 通過delegate.parseBeanDefinitionElement方法進行xml解析：

/**
 * 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}.
 */
@Nullable
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
	//解析id屬性
	String id = ele.getAttribute(ID_ATTRIBUTE);
	//解析name屬性
	String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);

	//分割name屬性
	List<String> aliases = new ArrayList<>();
	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.isTraceEnabled()) {
			logger.trace("No XML 'id' specified - using '" + beanName +
					"' as bean name and " + aliases + " as aliases");
		}
	}

	if (containingBean == null) {
		checkNameUniqueness(beanName, aliases, ele);
	}
	//將資訊封裝到 beanDefinition中
	AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
	if (beanDefinition != null) {
		if (!StringUtils.hasText(beanName)) {
			try {
				//beanname不存在則使用預設規則建立
				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.isTraceEnabled()) {
					logger.trace("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;
}

在parseBeanDefinitionElement方法中做了三件事：

1：解析id/name；

2：檢查name的唯一性；

3：將資訊封裝到 beanDefinition中，接下來直接看parseBeanDefinitionElement方法；

• parseBeanDefinitionElement原始碼：

/**
 * 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.
 */
@Nullable
public AbstractBeanDefinition parseBeanDefinitionElement(
		Element ele, String beanName, @Nullable BeanDefinition containingBean) {
	this.parseState.push(new BeanEntry(beanName));

	String className = null;
	//解析classname屬性
	if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
		className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
	}
	String parent = null;
	//解析parent屬性
	if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
		parent = ele.getAttribute(PARENT_ATTRIBUTE);
	}

	try {
		//建立用於承載屬性的AbstractBeanDefinition型別的
		AbstractBeanDefinition bd = createBeanDefinition(className, parent);

		//解析bean的各種屬性
		parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
		//提取description
		bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));

		//解析meta （後設資料）
		parseMetaElements(ele, bd);

		//解析Lookup-method 書中53頁有使用方法
		parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
		//解析replaced-method 書中55頁有使用方法
		parseReplacedMethodSubElements(ele, bd.getMethodOverrides());

		//建構函式 引數
		//解析constructor-arg 書中replaced-method後邊
		parseConstructorArgElements(ele, bd);
		//解析Property 書中replaced-method後邊
		parsePropertyElements(ele, bd);
		//解析Qualifier 書中Property後邊
		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;
}

通過上述程式碼我們可以看到這裡首先是例項化了一個AbstractBeanDefinition來承載各種xml屬性，接下來通過parseBeanDefinitionAttributes方法解析了xml中的各種你屬性值，然後在解析lookUp-method(方法注入)，replaced-method(替換方法或方法返回值)，建構函式引數constructor-arg，property屬性，Qualifier屬性等；上述方法的原始碼就不一一展示了，無非都是通過Element進行解析；

• 接下來看真正註冊的程式碼 BeanDefinitionReaderUtils.registerBeanDefinition

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

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

	if (beanDefinition instanceof AbstractBeanDefinition) {
		try {
			//校驗 MethodOverrides，MethodOverrides在解析並組裝beanDefinition時有提到
			((AbstractBeanDefinition) beanDefinition).validate();
		}
		catch (BeanDefinitionValidationException ex) {
			throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Validation of bean definition failed", ex);
		}
	}

	//beanDefinitionMap 儲存例項的全域性Map 使用ConcurrentHashMap 執行緒安全
	BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
	//如果已經註冊 處理內容
	if (existingDefinition != null) {
		//是否覆蓋
		if (!isAllowBeanDefinitionOverriding()) {
			throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
		}
		else if (existingDefinition.getRole() < beanDefinition.getRole()) {
			// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
			if (logger.isInfoEnabled()) {
				logger.info("Overriding user-defined bean definition for bean '" + beanName +
						"' with a framework-generated bean definition: replacing [" +
						existingDefinition + "] with [" + beanDefinition + "]");
			}
		}
		else if (!beanDefinition.equals(existingDefinition)) {
			if (logger.isDebugEnabled()) {
				logger.debug("Overriding bean definition for bean '" + beanName +
						"' with a different definition: replacing [" + existingDefinition +
						"] with [" + beanDefinition + "]");
			}
		}
		else {
			if (logger.isTraceEnabled()) {
				logger.trace("Overriding bean definition for bean '" + beanName +
						"' with an equivalent definition: replacing [" + existingDefinition +
						"] with [" + beanDefinition + "]");
			}
		}
		this.beanDefinitionMap.put(beanName, beanDefinition);
	}
	else {
		//判斷是否已經至少建立過一次 使用AbstractBeanFactory.alreadyCreated來判斷
		if (hasBeanCreationStarted()) {
			// Cannot modify startup-time collection elements anymore (for stable iteration)
			synchronized (this.beanDefinitionMap) {
				this.beanDefinitionMap.put(beanName, beanDefinition);
				List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
				updatedDefinitions.addAll(this.beanDefinitionNames);
				updatedDefinitions.add(beanName);
				this.beanDefinitionNames = updatedDefinitions;
				if (this.manualSingletonNames.contains(beanName)) {
					Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
					updatedSingletons.remove(beanName);
					this.manualSingletonNames = updatedSingletons;
				}
			}
		}
		else {
			// 仍處於啟動註冊階段
			// 註冊 beanDefinitionMap 新例項 beanName + beanDefinition
			this.beanDefinitionMap.put(beanName, beanDefinition);
			// 增加beanDefinitionNames
			this.beanDefinitionNames.add(beanName);
			// 清除快取
			this.manualSingletonNames.remove(beanName);
		}
		// 清除快取
		this.frozenBeanDefinitionNames = null;
	}

	if (existingDefinition != null || containsSingleton(beanName)) {
		resetBeanDefinition(beanName);
	}
}

上述程式碼中首先驗證了beanName和BeannDefinition不可為空,然後繼續校驗了MethodOverridesMethodOverrides在解析並組裝beanDefinition時lookup-method和recpse-method的原始碼中有提到，繼續判斷beanDefinitionMap是否存在該bean，如果bean已經存在，通過allowBeanDefinitionOverriding屬性判斷是否可覆蓋，反之則丟擲異常；如果不存在則需要判斷本次是否是第一次註冊bean，如果是則初始化beanDefinitionMap後進行put操作，反之直接put beanDefinitionMap完成註冊；

至此我們已經看完了整個XmlBeanFactory的xml解析和註冊的原始碼部分，相信看本篇文章無法真正理解，還需要讀者下載原始碼使用debug執行，再結合本篇文章的註釋，相信會很容易理解，碼字不易，轉發請註明出處。