spring中xml配置bean加載解析流程

當我們以ClassPathXmlApplicationContext啓動的時候，在實際啓動容器的
AbstractAppliationContext.refresh
spring容器啓動流程
跟蹤代碼，在

AbstractApplicationContext.obtainFreshBeanFactory();
其在refreshBeanFactory實現具體邏輯

protected final void refreshBeanFactory() throws BeansException {
		//如果已經有了BeanFactory先銷燬關閉它
		if (hasBeanFactory()) {
			destroyBeans();
			closeBeanFactory();
		}
		try {
			//直接new 了一個 DefaultListableBeanFactory，
			// 並且在其繼承父類中 AbstractAutowireCapableBeanFactory配置忽略自動裝配的配置
			DefaultListableBeanFactory beanFactory = createBeanFactory();
			beanFactory.setSerializationId(getId());
			customizeBeanFactory(beanFactory);
			//這是重要的步驟，加載所有bean的配置，這是一個模板方法，由具體子類去實現
			loadBeanDefinitions(beanFactory);
			synchronized (this.beanFactoryMonitor) {
				this.beanFactory = beanFactory;
			}
		}
		catch (IOException ex) {
			throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
		}
	}

可以發現，這裏調用了loadBeanDefinitions方法來加載bean的定義信息，

這裏是一個模板方法，其實現有圖示幾種方式，這裏我們用比較原始的XML爲例來說明。

AbstractXmlApplicationContext.loadBeanDefinitions

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.setEnvironment(this.getEnvironment());
		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);
	}

可以看到，主要是兩步，初始化一個XmlBeanDefinitionReader，然後將beanDefinition加載註冊。

繼續跟進 loadBeanDefinitions方法，這裏就是根據不同配置來讀取相應的配置文件。

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);
		}
	}

最終都是調用

XmlBeanDefinitionReader.loadBeanDefinitions

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

然後在doLoadBeanDefinitions進行配置文件的解析

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
			throws BeanDefinitionStoreException {

		try {
			Document doc = doLoadDocument(inputSource, resource);
			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);
		}
	}

從方法字面含義上看，主要是幹了兩件事情：

將配置文件轉換爲xml結構，返回一個Document
將解析出來的Document解析成BeanDefinitions並註冊

繼續跟蹤，在DefaultBeanDefinitionDocumentReader裏進行Document的解析。

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);

		if (this.delegate.isDefaultNamespace(root)) {
			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;
				}
			}
		}

		preProcessXml(root);
		parseBeanDefinitions(root, this.delegate);
		postProcessXml(root);

		this.delegate = parent;
	}

其中preProcessXml是一個空的實現。
跟蹤parseBeanDefinitions

protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
		if (delegate.isDefaultNamespace(root)) {
			NodeList nl = root.getChildNodes();
			for (int i = 0; i < nl.getLength(); i++) {
				Node node = nl.item(i);
				if (node instanceof Element) {
					Element ele = (Element) node;
					if (delegate.isDefaultNamespace(ele)) {
						parseDefaultElement(ele, delegate);
					}
					else {
						delegate.parseCustomElement(ele);
					}
				}
			}
		}
		else {
			delegate.parseCustomElement(root);
		}
	}

可以發現這裏會對spring默認提供的xml標籤進行解析，以及用戶自定義的標籤進行解析

TO-DO：spring中spring.handler文件作用

parseDefaultElement方法如下：

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);
		}
	}

一次對import,alias,bean,beans這四中標籤進行解析，我們以最常見的bean標籤解析進行說明。

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
		BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
		if (bdHolder != null) {
			//解析自定義標籤和屬性
			bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
			try {
				// Register the final decorated instance.
				//註冊BeanDefinitionHolder
				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));
		}
	}

通過BeanDefinitionParserDelegate解析代理解析bean標籤
解析自定義標籤和屬性
註冊bean定義信息
發送bean定義註冊註冊事件

接下來我們詳細看下bean標籤的解析詳細邏輯，代碼實現如下，這裏主要是實際解析前的一些工作，比如beanName是不是存在等，確保bean標籤內容可以被解析

public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
		//獲取bean標籤中定義的id信息
		String id = ele.getAttribute(ID_ATTRIBUTE);
		//獲取bean標籤中定義的name信息
		String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
		List<String> aliases = new ArrayList<>();
		//如果name中包含逗號或者分號，進行分隔，並保存到aliases中
		if (StringUtils.hasLength(nameAttr)) {
			String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
			aliases.addAll(Arrays.asList(nameArr));
		}
		String beanName = id;
		// 如果beanName爲空，且aliases不爲空，取aliases中第一個作爲beanName，
		// 否則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");
			}
		}
		//檢察beanName和aliases是否已經被使用過，如果已經使用過則會拋出異常
		if (containingBean == null) {
			checkNameUniqueness(beanName, aliases, ele);
		}
		// 進行bean標籤的解析，返回的是一個 GenericBeanDefinition
		AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
		if (beanDefinition != null) {
			// 如果beanName爲空，生成beanName
			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.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;
	}

這裏面，bean標籤解析的方法public AbstractBeanDefinition parseBeanDefinitionElement( Element ele, String beanName, @Nullable BeanDefinition containingBean),這裏是對bean標籤進行解析了：

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

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

		String className = null;
		//解析class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 {
			// 創建BeanDefinition,返回的是 GenericBeanDefinition，這裏的BeanDefinition實際上沒有什麼內容，需要繼續填充
			AbstractBeanDefinition bd = createBeanDefinition(className, parent);
			//解析bean的相關屬性
			parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
			//獲取description屬性
			bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
			//解析bean子標籤meta屬性
			parseMetaElements(ele, bd);
			//解析bean子標籤lookup-method
			parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
			//解析bean子標籤replaced-method
			parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
			//解析bean子標籤constructor-arg
			parseConstructorArgElements(ele, bd);
			//解析bean子標籤property
			parsePropertyElements(ele, bd);
			//解析bean子標籤qualifier
			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;
	}

可以看到，這裏解析bean標籤主要如下幾步：

解析class和parent屬性
創建一個BeanDefinition用來裝載解析的bean的標籤內容
解析bean的相關屬性
解析description屬性
解析bean子標籤meta屬性
解析bean子標籤lookup-method
解析bean子標籤replaced-method
解析bean子標籤constructor-arg
解析bean子標籤property
解析bean子標籤qualifier

這裏面第二步生成的BeanDefinition其實是一個空的，後續會對它填充。
我們首先來看

parseBeanDefinitionAttributes

這裏會解析<bean>標籤相關屬性，詳細實現如下：

public AbstractBeanDefinition parseBeanDefinitionAttributes(Element ele, String beanName,
			@Nullable BeanDefinition containingBean, AbstractBeanDefinition bd) {
		//不在支持singleton屬性
		if (ele.hasAttribute(SINGLETON_ATTRIBUTE)) {
			error("Old 1.x 'singleton' attribute in use - upgrade to 'scope' declaration", ele);
		}
		//解析scope屬性
		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());
		}
		// 解析abstract屬性
		if (ele.hasAttribute(ABSTRACT_ATTRIBUTE)) {
			bd.setAbstract(TRUE_VALUE.equals(ele.getAttribute(ABSTRACT_ATTRIBUTE)));
		}
		// 解析lazy-init屬性
		String lazyInit = ele.getAttribute(LAZY_INIT_ATTRIBUTE);
		if (isDefaultValue(lazyInit)) {
			lazyInit = this.defaults.getLazyInit();
		}
		bd.setLazyInit(TRUE_VALUE.equals(lazyInit));
		// 解析autowire屬性
		String autowire = ele.getAttribute(AUTOWIRE_ATTRIBUTE);
		bd.setAutowireMode(getAutowireMode(autowire));
		// 解析depends-on屬性
		if (ele.hasAttribute(DEPENDS_ON_ATTRIBUTE)) {
			String dependsOn = ele.getAttribute(DEPENDS_ON_ATTRIBUTE);
			bd.setDependsOn(StringUtils.tokenizeToStringArray(dependsOn, MULTI_VALUE_ATTRIBUTE_DELIMITERS));
		}
		// 解析autowire-candidate屬性
		String autowireCandidate = ele.getAttribute(AUTOWIRE_CANDIDATE_ATTRIBUTE);
		if (isDefaultValue(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));
		}
		// 解析primary屬性
		if (ele.hasAttribute(PRIMARY_ATTRIBUTE)) {
			bd.setPrimary(TRUE_VALUE.equals(ele.getAttribute(PRIMARY_ATTRIBUTE)));
		}
		// 解析init-method屬性
		if (ele.hasAttribute(INIT_METHOD_ATTRIBUTE)) {
			String initMethodName = ele.getAttribute(INIT_METHOD_ATTRIBUTE);
			bd.setInitMethodName(initMethodName);
		}
		else if (this.defaults.getInitMethod() != null) {
			bd.setInitMethodName(this.defaults.getInitMethod());
			bd.setEnforceInitMethod(false);
		}
		// 解析destroy-method屬性
		if (ele.hasAttribute(DESTROY_METHOD_ATTRIBUTE)) {
			String destroyMethodName = ele.getAttribute(DESTROY_METHOD_ATTRIBUTE);
			bd.setDestroyMethodName(destroyMethodName);
		}
		else if (this.defaults.getDestroyMethod() != null) {
			bd.setDestroyMethodName(this.defaults.getDestroyMethod());
			bd.setEnforceDestroyMethod(false);
		}
		// 解析factory-method屬性
		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，主要是解析如下<bean>標籤相關屬性。

scope
abstract
lazy-init
autowire
depends-on
autowire-candidate
primary
init-method
destroy-method
factory-method
到這裏<bean>標籤的相關屬性就全部解析完成，會填充到BeanDifinition中去。

當執行完BeanDefinitionParserDelegate.parseBeanDefinitionElement之後，一個BeaDefinition基本完成，回到DefaultBeanDefinitionDocumentReader.processBeanDefinition方法中，當BeanDefinition填充完畢之後，接下來就是將它註冊到容器中：

BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());

這個方法的實現邏輯如下：

public static void registerBeanDefinition(
			BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
			throws BeanDefinitionStoreException {

		// Register bean definition under primary name.
		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 alias : aliases) {
				registry.registerAlias(beanName, alias);
			}
		}
	}

可以看到，註冊BeanDefinition主要分爲兩步：

按照beanName註冊
根據bean的aliases註冊

首先來看按照beanName註冊BeanDefinition（以DefaultListableBeanFactory爲例說明）：

DefaultListableBeanFactory.registerBeanDefinition

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");
		// XML配置的這裏爲true會進入執行，進行註冊前的校驗
		if (beanDefinition instanceof AbstractBeanDefinition) {
			try {
				((AbstractBeanDefinition) beanDefinition).validate();
			}
			catch (BeanDefinitionValidationException ex) {
				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Validation of bean definition failed", ex);
			}
		}

		BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
		//判斷BeanDefinition是否已經註冊過，如果註冊過且允許覆蓋按照條件是否覆蓋BeanDefinition
		if (existingDefinition != null) {
			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 {
			//如果已經開始創建bean，會進行鎖定
			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;
					removeManualSingletonName(beanName);
				}
			}
			else {
				// Still in startup registration phase
				this.beanDefinitionMap.put(beanName, beanDefinition);
				this.beanDefinitionNames.add(beanName);
				// 非容器自動加載，手動註冊的單例中是否包含當前BeanDefinition，如果包含會移除註冊當前BeanDefinition
				removeManualSingletonName(beanName);
			}
			this.frozenBeanDefinitionNames = null;
		}
		// BeanDefinition已經註冊過，或者
		// 非容器自動加載，手動註冊的單例中是否包含當前BeanDefinition，
		// 滿足這兩個條件任意一個觸發該方法
		if (existingDefinition != null || containsSingleton(beanName)) {
			resetBeanDefinition(beanName);
		}
		// 參考啓動容器流程，當就緒之後創建容器會凍結配置，
		else if (isConfigurationFrozen()) {
			clearByTypeCache();
		}
	}

另外一個重要的解析流程是：

parseCustomElement

我們來看這個方法的實現：

public BeanDefinition parseCustomElement(Element ele, @Nullable BeanDefinition containingBd) {
		String namespaceUri = getNamespaceURI(ele);
		if (namespaceUri == null) {
			return null;
		}
		NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
		if (handler == null) {
			error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
			return null;
		}
		return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
	}

這裏會根據標籤的uri來獲取標籤對應NamespaceHandler，例如我們常見的·context·標籤。在每個spring不同模塊下都會存在一個META-INF/spring.handlers的文件，如spring-context下的sprin.handlers內容如下：

http\://www.springframework.org/schema/context=org.springframework.context.config.ContextNamespaceHandler
http\://www.springframework.org/schema/jee=org.springframework.ejb.config.JeeNamespaceHandler
http\://www.springframework.org/schema/lang=org.springframework.scripting.config.LangNamespaceHandler
http\://www.springframework.org/schema/task=org.springframework.scheduling.config.TaskNamespaceHandler
http\://www.springframework.org/schema/cache=org.springframework.cache.config.CacheNamespaceHandler

當遇到<context>標籤會去尋找context對應rui就是http\://www.springframework.org/schema/context
繼而其xml解決類爲：org.springframework.context.config.ContextNamespaceHandler,其內容如下：

public class ContextNamespaceHandler extends NamespaceHandlerSupport {

	@Override
	public void init() {
		registerBeanDefinitionParser("property-placeholder", new PropertyPlaceholderBeanDefinitionParser());
		registerBeanDefinitionParser("property-override", new PropertyOverrideBeanDefinitionParser());
		registerBeanDefinitionParser("annotation-config", new AnnotationConfigBeanDefinitionParser());
		registerBeanDefinitionParser("component-scan", new ComponentScanBeanDefinitionParser());
		registerBeanDefinitionParser("load-time-weaver", new LoadTimeWeaverBeanDefinitionParser());
		registerBeanDefinitionParser("spring-configured", new SpringConfiguredBeanDefinitionParser());
		registerBeanDefinitionParser("mbean-export", new MBeanExportBeanDefinitionParser());
		registerBeanDefinitionParser("mbean-server", new MBeanServerBeanDefinitionParser());
	}

}

可以發現，這裏只是注入了很多的Bean的解析類，當我們xml配置文件中遇到<context:component-scan>的時候，在

public BeanDefinition parseCustomElement(Element ele, @Nullable BeanDefinition containingBd) {
		String namespaceUri = getNamespaceURI(ele);
		if (namespaceUri == null) {
			return null;
		}
		// 獲取對應uri處理器，如 <context:component-scan>的時候，
		// 首先獲取<context>對應的uri處理器ContextNamespaceHandler，
		// 然後獲取ContextNamespaceHandler中註冊的component-scan的bean解析器
		NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
		if (handler == null) {
			error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
			return null;
		}
		return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
	}

這裏首先會獲取<context>對應NamespaceHandler，爲
ContextNamespaceHandler然後調用其parse方法，跟進方法，這個方法時在ContextNamespaceHandler的父類NamespaceHandlerSupport中：

@Override
	@Nullable
	public BeanDefinition parse(Element element, ParserContext parserContext) {
		BeanDefinitionParser parser = findParserForElement(element, parserContext);
		return (parser != null ? parser.parse(element, parserContext) : null);
	}

	/**
	 * Locates the {@link BeanDefinitionParser} from the register implementations using
	 * the local name of the supplied {@link Element}.
	 */
	@Nullable
	private BeanDefinitionParser findParserForElement(Element element, ParserContext parserContext) {
		String localName = parserContext.getDelegate().getLocalName(element);
		BeanDefinitionParser parser = this.parsers.get(localName);
		if (parser == null) {
			parserContext.getReaderContext().fatal(
					"Cannot locate BeanDefinitionParser for element [" + localName + "]", element);
		}
		return parser;
	}

這裏通過findParserForElement找到之前註冊component-scan註冊的bean解析器ComponentScanBeanDefinitionParser來解析，這樣完成了自定義擴展的標籤的解析。

至此bean的信息解析完成，並註冊到了對IOC容器中。
從整個流程中可以看到，主要是可以有兩個大的部分：

解析默認標籤，import、alias、bean、beans
其他標籤獲取uri對應的NameSpaceHandler來進行解析

解析完這些之後，會將bean的信息，beanName，alias信息註冊到IOC容器中，以便後續生成bean

spring中xml配置bean加載解析流程

SQL優化-20231016

Mybatis入門，Mybatis運行原理剖析，Mybatis源碼研究，StatementHandler，TypeHandler,SimpleExecutor，ResultHandler

5. Mybatis入門，ResultMap級聯，association，collection，discriminator，resultMap繼承，lazyLoadingEnabled

4. Mybatis入門，參數中#和$的區別

Mysql常用語句，查看數據庫，字段重命名，修改數據庫、表、字段字符集

3. Mybatis入門，動態sql，if條件，choose，trim，foreach循環，bind

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