上一篇我们通过refresh方法中的第二个核心方法obtainBeanFactory，通过createBeanFacotry创建容Spring的初级容器，并定义了容器的两个核心参数是否允许循环引用和覆盖。现在容器有了，我们来看看容器里的第一个重要成员BeanDefinition。

进入loadBeanDefinitions方法

/*** Loads the bean definitions via an XmlBeanDefinitionReader.* @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader* @see #initBeanDefinitionReader* @see #loadBeanDefinitions*/@Overrideprotected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {// Create a new XmlBeanDefinitionReader for the given BeanFactory.// 初始化XmlBeanDefinitionReader：xml阅读器XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);// Configure the bean definition reader with this context's resource loading environment.// 配置BeanDefinition上下文信息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.// 看到规律了呢，Allow a subclass 基本上都是Spring 预留的扩展点，空实现，留给子类自己去自定义initBeanDefinitionReader(beanDefinitionReader);// 通过beanDefinitionReader去加载解析xml中的BeanDefinitionloadBeanDefinitions(beanDefinitionReader);}

 BeanDefinitionReader 加载BeanDefinition

委托BeanDefinition阅读器去加载BeanDefinition，如下代码：

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/*** Load the bean definitions with the given XmlBeanDefinitionReader.* <p>The lifecycle of the bean factory is handled by the {@link #refreshBeanFactory}* method; hence this method is just supposed to load and/or register bean definitions.* @param reader the XmlBeanDefinitionReader to use* @throws BeansException in case of bean registration errors* @throws IOException if the required XML document isn't found* @see #refreshBeanFactory* @see #getConfigLocations* @see #getResources* @see #getResourcePatternResolver*/protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {Resource[] configResources = getConfigResources();if (configResources != null) {reader.loadBeanDefinitions(configResources);}// 获取我们前面封装好的xml文件名对应的string数组；String[] configLocations = getConfigLocations();if (configLocations != null) {reader.loadBeanDefinitions(configLocations);}}public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {Assert.notNull(locations, "Location array must not be null");int count = 0;for (String location : locations) {count += loadBeanDefinitions(location);}return count;}public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {return loadBeanDefinitions(location, null);}​

Resource -- > EncodedResource

将我们传入的location委托给Resource解析器生成Resource对象or Resource对象列表，通过Resour：将resource包装成EncodedResource对象，开始加载Bean Definition

	/*** Load bean definitions from the specified XML file. 通过指定的XML文件 加载BeanDefinition* @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 {Assert.notNull(encodedResource, "EncodedResource must not be null");if (logger.isTraceEnabled()) {logger.trace("Loading XML bean definitions from " + encodedResource);}Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();if (!currentResources.add(encodedResource)) {throw new BeanDefinitionStoreException("Detected cyclic loading of " + encodedResource + " - check your import definitions!");}try (InputStream inputStream = encodedResource.getResource().getInputStream()) {InputSource inputSource = new InputSource(inputStream);if (encodedResource.getEncoding() != null) {inputSource.setEncoding(encodedResource.getEncoding());}return doLoadBeanDefinitions(inputSource, encodedResource.getResource()); // 真正开始处理xml转BeanDefinition}catch (IOException ex) {throw new BeanDefinitionStoreException("IOException parsing XML document from " + encodedResource.getResource(), ex);}finally {currentResources.remove(encodedResource);if (currentResources.isEmpty()) {this.resourcesCurrentlyBeingLoaded.remove();}}}

doLoadBeanDefinitions -- >Document

registerBeanDefiniton

	public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();int countBefore = getRegistry().getBeanDefinitionCount();documentReader.registerBeanDefinitions(doc, createReaderContext(resource));// 委托documentReader 注册BeanDefinitionreturn getRegistry().getBeanDefinitionCount() - countBefore;}/*** 根据xsd或dtd解析xml*/@Overridepublic void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {this.readerContext = readerContext;doRegisterBeanDefinitions(doc.getDocumentElement()); // 真正开始注册}

do RegisterBeanDefinitions

/*** 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); // 创建BeanDefinition解析器委托类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); // 扩展点加一：空实现，委托子类自定义parseBeanDefinitions(root, this.delegate); // 解Bean定义类标签如： "import", "alias", "bean".postProcessXml(root); //this.delegate = parent;}

parseBeanDefinition

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);}}private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) { // 是否包含：import标签importBeanDefinitionResource(ele);}else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) { // 是否包含：alias标签processAliasRegistration(ele);}else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) { // 单个bean标签处理processBeanDefinition(ele, delegate);}else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {// recursedoRegisterBeanDefinitions(ele);}}

processBeanDefinition

	protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele); // BeanDefinition解析器委托类，解析源文件要素，返回BeanDefinition包装类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));}}

BeanDefinitionReaderUtils.registerBeanDefiniton

/*** 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 {// 名称，作为BeanDefinition容器的keyString beanName = definitionHolder.getBeanName();// beanName作为key BeanDefinition作为value放入Bean Factory容器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);}}}

BeanDefinition注入Bean Factory容器

//---------------------------------------------------------------------// Implementation of BeanDefinitionRegistry interface 实现BeanDefinitionRegistry接口// 这段代码是将BeanDefinition实例放入容器的地方//---------------------------------------------------------------------@Overridepublic 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 {((AbstractBeanDefinition) beanDefinition).validate();}catch (BeanDefinitionValidationException ex) {throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,"Validation of bean definition failed", ex);}}// 先查询下beanName对应的BeanDefinition是否存在BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);if (existingDefinition != null) { // 如果存在且步云熙覆盖则抛出异常if (!isAllowBeanDefinitionOverriding()) {throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);}else if (existingDefinition.getRole() < beanDefinition.getRole()) { // 否则重写// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTUREif (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); // 覆盖}else {if (hasBeanCreationStarted()) {// ，在Spring框架的上下文中，一旦容器开始初始化Bean，就不能修改那些在启动时就设置好的集合元素//  检查Bean的创建过程是否已经开始。如果已经开始，那么在同步块内安全地更新Bean定义映射表和Bean定义名称列表，//  并将新的Bean定义添加到这些集合中。同时，从手动注册的单例Bean名称列表中移除新添加的Bean名称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;// 从手动注册的单例Bean集合中移除指定Bean名称removeManualSingletonName(beanName);}}else {//仍处于启动注册阶段 则 将beanName作为Key，BeanDefinition实例作为value 放入beanDefinitionMap容器中。this.beanDefinitionMap.put(beanName, beanDefinition);this.beanDefinitionNames.add(beanName);// 从手动注册的单例Bean集合中移除指定Bean名称removeManualSingletonName(beanName);}this.frozenBeanDefinitionNames = null;}if (existingDefinition != null || containsSingleton(beanName)) {// 重置BeanDefinitionresetBeanDefinition(beanName);}else if (isConfigurationFrozen()) {clearByTypeCache();}}