解析spring源码，IOC加载bean资源配置文件

一时失言乱红尘 2022-04-23 13:24 207阅读 0赞

> **本文主要内容及做什么**
> 
> 主要针对spring中的ioc，采用debug方式讲解spring如何加载bean配置文件，目的是对加载过程有个大概了解，spring源码优雅且复杂。

** 项目环境**

spring版本号为4.0.2，jdk1.8。

spring配置文件代码：

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
    	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    	xmlns:util="http://www.springframework.org/schema/util"
    	xmlns:p="http://www.springframework.org/schema/p"
    	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
    		http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-4.0.xsd">
    	
    	<bean id="person" class="com.test.service.PersonServiceImpl">
    		<property name="name" value="hello spring"></property>
    	</bean>
    	
    </beans>

test代码为：

public class test {
    	public static void main(String[] args) {
    		ApplicationContext cx = new ClassPathXmlApplicationContext("applicationContext.xml");
    		PersonServiceImpl obj = cx.getBean(PersonServiceImpl.class);
    		System.out.println(obj.toString());
    	}
    }

从上面可以看出，spring从拿到资源文件到创建并获取bean，从开发角度只需要两行代码可实现，但了解其内部原理也很重要，下面开始调试，断点进入 *ApplicationContext cx = new ClassPathXmlApplicationContext("applicationContext.xml");*  这一行代码。

1、按F5进入，进入到 ClassPathXmlApplicationContext 类的构造方法，方法第一行 super(parent);*** ***调用了父类的构造方法，父类为***AbstractXmlApplicationContext***，父类构造方法中同样super(parent)继续调用其父类，同样的方式分别调用了***AbstractRefreshableConfigApplicationContext，AbstractApplicationContext，DefaultResourceLoader；***一直调用父类构造方法，初始化了一个空的ApplicationContext对象。

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
    			throws BeansException {
    
    		super(parent);
    		setConfigLocations(configLocations);
    		if (refresh) {
    			refresh();
    		}
    	}

2、setConfigLocations(configLocations) 方法主要是解析spring的配置文件地址，并赋值到成员变量 private String\[\] configLocations 中，可以看到为数组类型，可配置多个。

3、进入 ***ClassPathXmlApplicationContext*** 类的 refresh() 方法，***ClassPathXmlApplicationContext ***类本身没实现refresh() 方法，而是继承了其父类 ***AbstractApplicationContext ***中的refresh() 方法，***AbstractApplicationContext ***是一个抽象类，refresh()是ApplicationContext初始化的核心，包含了初始化BeanFactory，解析XML加载BeanDefinition，注册bean处理器，注册事件添加监听等，以下为其refresh()代码：

@Override
    	public void refresh() throws BeansException, IllegalStateException {
    		synchronized (this.startupShutdownMonitor) {
    			// Prepare this context for refreshing.
    			prepareRefresh();
    			// Tell the subclass to refresh the internal bean factory.
    			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
    			// Prepare the bean factory for use in this context.
    			prepareBeanFactory(beanFactory);
    			try {
    				// Allows post-processing of the bean factory in context subclasses.
    				postProcessBeanFactory(beanFactory);
    				// Invoke factory processors registered as beans in the context.
    				invokeBeanFactoryPostProcessors(beanFactory);
    				// Register bean processors that intercept bean creation.
    				registerBeanPostProcessors(beanFactory);
    				// Initialize message source for this context.
    				initMessageSource();
    				// Initialize event multicaster for this context.
    				initApplicationEventMulticaster();
    				// Initialize other special beans in specific context subclasses.
    				onRefresh();
    				// Check for listener beans and register them.
    				registerListeners();
    				// Instantiate all remaining (non-lazy-init) singletons.
    				finishBeanFactoryInitialization(beanFactory);
    				// Last step: publish corresponding event.
    				finishRefresh();
    			}
    			catch (BeansException ex) {
    				// Destroy already created singletons to avoid dangling resources.
    				destroyBeans();
    				// Reset 'active' flag.
    				cancelRefresh(ex);
    				// Propagate exception to caller.
    				throw ex;
    			}
    		}
    	}

4、进入refresh()方法中的prepareRefresh()方法，主要是做些准备工作，记录开始时间，环境准备等。

/**
    	 * Prepare this context for refreshing, setting its startup date and
    	 * active flag as well as performing any initialization of property sources.
    	 */
    	protected void prepareRefresh() {
    		this.startupDate = System.currentTimeMillis();
    		synchronized (this.activeMonitor) {
    			this.active = true;
    		}
    		if (logger.isInfoEnabled()) {
    			logger.info("Refreshing " + this);
    		}
    		// Initialize any placeholder property sources in the context environment
    		initPropertySources();
    		// Validate that all properties marked as required are resolvable
    		// see ConfigurablePropertyResolver#setRequiredProperties
    		getEnvironment().validateRequiredProperties();
    	}

5、进入 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory() ，创建一个beanFactory，并且解析xml中的bean定义，放置在bean工厂当中，obtainFreshBeanFactory()方法代码：

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
    	refreshBeanFactory();
    	ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    	if (logger.isDebugEnabled()) {
    		logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
    	}
    	return beanFactory;
    }

6、进入refreshBeanFactory()方法，是在 ***AbstractRefreshableApplicationContext ***抽象类中，代码：

protected final void refreshBeanFactory() throws BeansException {
    		if (hasBeanFactory()) {
    			destroyBeans();
    			closeBeanFactory();
    		}
    		try {
    			DefaultListableBeanFactory beanFactory = createBeanFactory();
    			beanFactory.setSerializationId(getId());
    			customizeBeanFactory(beanFactory);
    			loadBeanDefinitions(beanFactory);
    			synchronized (this.beanFactoryMonitor) {
    				this.beanFactory = beanFactory;
    			}
    		}
    		catch (IOException ex) {
    			throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
    		}
    	}

它主要完成如下：

1）hasBeanFactory()判断当前context是否持有beanFactory，如果已经存在则销毁所有单例Bean的实例，再把当前beanFactory设置为null；

2）createBeanFactory()初始化新的beanFactory，类型为DefaultListableBeanFactory；

3）customizeBeanFactory(beanFactory)设定beanFactory的一些属性；

4）loadBeanDefinitions(beanFactory)加载BeanDefinitions，这是最为核心的一步

7、进入 DefaultListableBeanFactory beanFactory = createBeanFactory()方法，直接新创建了一个 DefaultListableBeanFactory类型的beanFactory并且返回，在创建的同时初始化存放bean相关属性的缓存，一般都是使用Hahsmap或者ConcurrentHashMap；

protected DefaultListableBeanFactory createBeanFactory() {
    		return new DefaultListableBeanFactory(getInternalParentBeanFactory());
    	}

8、返回来进入 refreshBeanFactory() 方法中关键的方法 loadBeanDefinitions(beanFactory)，在抽象类 ***AbstractXmlApplicationContext*** 中，传入了创建好的beanFactory，代码：

/**
    	 * Loads the bean definitions via an XmlBeanDefinitionReader.
    	 * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
    	 * @see #initBeanDefinitionReader
    	 * @see #loadBeanDefinitions
    	 */
    	@Override
    	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);
    	}

9、来看 XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory) 这行代码，新建读取器 XmlBeanDefinitionReader，Reader是用来读取并解析xml文件，***XmlBeanDefinitionReader ***为抽象类，***XmlBeanDefinitionReader ***实现了 ***BeanDefinitionReader*** 接口，覆写了loadBeanDefinitions方法。

10、进入关键方法 loadBeanDefinitions(beanDefinitionReader)：

/**
    	 * 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);
    		}
    		String[] configLocations = getConfigLocations();
    		if (configLocations != null) {
    			reader.loadBeanDefinitions(configLocations);
    		}
    	}

注解说的是用 XmlBeanDefinitionReader 读取器加载bean定义，其中出现了两重载方法loadBeanDefinitions()，来看下getConfigResources()方法是怎么定义的：

***ClassPathXmlApplicationContext*** 类中的方法：

protected Resource[] getConfigResources() {
    	return this.configResources;
    }

***AbstractRefreshableConfigApplicationContext ***为 ***ClassPathXmlApplicationContext*** 父类，

***AbstractRefreshableConfigApplicationContext*** 抽象类中的方法：

protected String[] getConfigLocations() {
    		return (this.configLocations != null ? this.configLocations : getDefaultConfigLocations());
    	}

可以看到是获取 ***ApplicationContext ***子类的常量值，所以，到底是configLocations 还是configResources ，与最初实例化ClassPathXmlApplicationContext 对象选择的构造方法相关，实例化 applicationContext 对象的方式是new ClassPathXmlApplicationContext(“applicationContext.xml”)，那么setConfigLocations方法就会被调用：

String[] configLocations = getConfigLocations();
    		if (configLocations != null) {
    			reader.loadBeanDefinitions(configLocations);
    		}

11、进入 reader.loadBeanDefinitions(configLocations) 方法，进入了 ***AbstractBeanDefinitionReader ***抽象类，它为***XmlBeanDefinitionReader ***类的父类，

public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
    		Assert.notNull(locations, "Location array must not be null");
    		int counter = 0;
    		for (String location : locations) {
    			counter += loadBeanDefinitions(location);
    		}
    		return counter;
    	}

这个方法返回值为所找到的bean定义的个数，但是这里可以看出，在调用它的方法内并没有接收和使用这个返回值。

在最初设定的资源路径为classpath下的applicationContext.xml，所以这个方法的参数值为\[applicationContext.xml\]

12，进入loadBeanDefinitions(location)方法：

public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {
    		return loadBeanDefinitions(location, null);
    	}

再进去：

public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
    		ResourceLoader resourceLoader = getResourceLoader();
    		if (resourceLoader == null) {
    			throw new BeanDefinitionStoreException(
    					"Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
    		}
    
    		if (resourceLoader instanceof ResourcePatternResolver) {
    			// Resource pattern matching available.
    			try {
    				Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
    				int loadCount = loadBeanDefinitions(resources);
    				if (actualResources != null) {
    					for (Resource resource : resources) {
    						actualResources.add(resource);
    					}
    				}
    				if (logger.isDebugEnabled()) {
    					logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
    				}
    				return loadCount;
    			}
    			catch (IOException ex) {
    				throw new BeanDefinitionStoreException(
    						"Could not resolve bean definition resource pattern [" + location + "]", ex);
    			}
    		}
    		else {
    			// Can only load single resources by absolute URL.
    			Resource resource = resourceLoader.getResource(location);
    			int loadCount = loadBeanDefinitions(resource);
    			if (actualResources != null) {
    				actualResources.add(resource);
    			}
    			if (logger.isDebugEnabled()) {
    				logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
    			}
    			return loadCount;
    		}
    	}

首先getResourceLoader()获取初始化applicationcontext过程中设置的资源加载器，断定是否为ResourcePatternResolver类型。

进入if中的 loadBeanDefinitions(resources) 方法：

public int loadBeanDefinitions(Resource... resources) throws BeanDefinitionStoreException {
    		Assert.notNull(resources, "Resource array must not be null");
    		int counter = 0;
    		for (Resource resource : resources) {
    			counter += loadBeanDefinitions(resource);
    		}
    		return counter;
    	}

13，进入loadBeanDefinitions()，发现从***AbstractBeanDefinitionReader ***抽象类跳到 ***XmlBeanDefinitionReader ***类，***AbstractBeanDefinitionReader ***为 ***XmlBeanDefinitionReader ***的父类：

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

上述代码把Resource对象包装成EncodedResource对象，

再进到 loadBeanDefinitions() 方法中：

public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
    		Assert.notNull(encodedResource, "EncodedResource must not be null");
    		if (logger.isInfoEnabled()) {
    			logger.info("Loading XML bean definitions from " + encodedResource.getResource());
    		}
    
    		Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
    		if (currentResources == null) {
    			currentResources = new HashSet<EncodedResource>(4);
    			this.resourcesCurrentlyBeingLoaded.set(currentResources);
    		}
    		if (!currentResources.add(encodedResource)) {
    			throw new BeanDefinitionStoreException(
    					"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
    		}
    		try {
    			InputStream inputStream = encodedResource.getResource().getInputStream();
    			try {
    				InputSource inputSource = new InputSource(inputStream);
    				if (encodedResource.getEncoding() != null) {
    					inputSource.setEncoding(encodedResource.getEncoding());
    				}
    				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();
    			}
    		}
    	}

上述方法中获取了资源的InputSource源，InputSource类为处理XML文件辅助类

14、进入 doLoadBeanDefinitions(inputSource, encodedResource.getResource()) 方法：

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
    			throws BeanDefinitionStoreException {
    		try {
    			Document doc = doLoadDocument(inputSource, resource);
    			return registerBeanDefinitions(doc, resource);
    		}
    		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);
    		}
    	}

doLoadDocument(inputSource, resource) 方法返回的资源的Document对象

15，进入 registerBeanDefinitions(doc, resource) 方法中：

/**
    	 * 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 {
    		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
    		documentReader.setEnvironment(this.getEnvironment());
    		int countBefore = getRegistry().getBeanDefinitionCount();
    		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
    		return getRegistry().getBeanDefinitionCount() - countBefore;
    	}

看注解，Register the bean definitions contained in the given DOM document，从给定的dom对象中注册bean定义。

首先创建了 BeanDefinitionDocumentReader 对象，***BeanDefinitionDocumentReader***类有两个作用，完成 BeanDefinition 的解析和注册。

int countBefore = getRegistry().getBeanDefinitionCount()获取先前存在的BeanDefinition个数，用于计算新注册的BeanDefinition个数。

进入 getBeanDefinitionCount() 方法，***DefaultListableBeanFactory***类中的getBeanDefinitionCount()方法：

public int getBeanDefinitionCount() {
    		return this.beanDefinitionMap.size();
    	}

/** Map of bean definition objects, keyed by bean name */
    private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(64);

beanDefinitionMap是个ConcurrentHashMap，用于存放bean，key为String类型，value为BeanDefinition类型，BeanDefinition是一个接口，具有很多类型的实现子类，spring默认使用其子类***GenericBeanDefinition***，***GenericBeanDefinition***属性很少，大部分的继承自***AbstractBeanDefinition***类。至于 ***DefaultListableBeanFactory ***类，很多人都说 ***DefaultListableBeanFactory ***是spring ioc最为核心的类，说它是spring ioc的发动机，聚集了ioc大部分核心公共方法和受保护的方法。

由于之前没有注册过BeanDefinition，所以countBefore值为0。

16、进入documentReader.registerBeanDefinitions(doc, createReaderContext(resource))：

public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
    		this.readerContext = readerContext;
    		logger.debug("Loading bean definitions");
    		Element root = doc.getDocumentElement();
    		doRegisterBeanDefinitions(root);
    	}

获取了dom对象的root根元素。

17、进入 doRegisterBeanDefinitions() 方法：

/**
    	 * Register each bean definition within the given root {@code <beans/>} element.
    	 * @throws IllegalStateException if {@code <beans profile="..."} attribute is present
    	 * and Environment property has not been set
    	 * @see #setEnvironment
    	 */
    	protected void doRegisterBeanDefinitions(Element root) {
    		String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
    		if (StringUtils.hasText(profileSpec)) {
    			Assert.state(this.environment != null, "Environment must be set for evaluating profiles");
    			String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
    					profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
    			if (!this.environment.acceptsProfiles(specifiedProfiles)) {
    				return;
    			}
    		}
    
    		// 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(this.readerContext, root, parent);
    
    		preProcessXml(root);
    		parseBeanDefinitions(root, this.delegate);
    		postProcessXml(root);
    
    		this.delegate = parent;
    	}

18、parseBeanDefinitions 方法传入了资源文件的根元素和新建的代理对象，进入 parseBeanDefinitions(root, this.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)) {
    			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);
    		}
    	}

parseDefaultElement 是对根元素一步一步解析，当解析到定义好的<bean>元素时，node即为Element，强制转换为Element，进入了元素解析 parseDefaultElement(ele, delegate) 方法。

19、进入parseDefaultElement(ele, delegate)：

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);
    		}
    	}

这里判断资源文件中设置bean格式，最初是用普通bean定义的形式，BEAN\_ELEMENT的值为"bean"。

20、进入processBeanDefinition(ele, delegate)：

/**
    	 * 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));
    		}
    	}

利用代理对象创建了一个BeanDefinition持有者，作为参数。

21、进入 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.
    		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);
    			}
    		}
    	}

取到 definitionHolder 的beanname为资源文件bean的id值，definitionHolder.getBeanDefinition()返回对象为 BeanDefinition 类型，其封装了bean定的类的全路径和相应的属性值。

22、进入 registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition())：

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 {
    			((AbstractBeanDefinition) beanDefinition).validate();
    		}
    		catch (BeanDefinitionValidationException ex) {
    			throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
    						"Validation of bean definition failed", ex);
    		}
    	}
    
    	synchronized (this.beanDefinitionMap) {
    		BeanDefinition 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 {
    			this.beanDefinitionNames.add(beanName);
    			this.frozenBeanDefinitionNames = null;
    		}
    		this.beanDefinitionMap.put(beanName, beanDefinition);
    	}
    
    	resetBeanDefinition(beanName);
    }

/** List of bean definition names, in registration order */
    	private final List<String> beanDefinitionNames = new ArrayList<String>();

/** Map of bean definition objects, keyed by bean name */
    	private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(64);

beanDefinitionMap 是存放bean的Map，使用synchronized锁住避免多线程问题，再把 beanDefinitionput 进 beanDefinitionMap中存放起来，bean的id作为key值，可见，spring存放我们通常定义的bean就是使用初始容量为64的ConcurrentHashMap。

23、 看resetBeanDefinition：

/**
    	 * Reset all bean definition caches for the given bean,
    	 * including the caches of beans that are derived from it.
    	 * @param beanName the name of the bean to reset
    	 */
    	protected void resetBeanDefinition(String beanName) {
    		// Remove the merged bean definition for the given bean, if already created.
    		clearMergedBeanDefinition(beanName);
    
    		// Remove corresponding bean from singleton cache, if any. Shouldn't usually
    		// be necessary, rather just meant for overriding a context's default beans
    		// (e.g. the default StaticMessageSource in a StaticApplicationContext).
    		destroySingleton(beanName);
    
    		// Remove any assumptions about by-type mappings.
    		clearByTypeCache();
    
    		// Reset all bean definitions that have the given bean as parent (recursively).
    		for (String bdName : this.beanDefinitionNames) {
    			if (!beanName.equals(bdName)) {
    				BeanDefinition bd = this.beanDefinitionMap.get(bdName);
    				if (beanName.equals(bd.getParentName())) {
    					resetBeanDefinition(bdName);
    				}
    			}
    		}
    	}

/**
    	 * Remove the merged bean definition for the specified bean,
    	 * recreating it on next access.
    	 * @param beanName the bean name to clear the merged definition for
    	 */
    	protected void clearMergedBeanDefinition(String beanName) {
    		this.mergedBeanDefinitions.remove(beanName);
    	}

resetBeanDefinition 方法的参数只有一个，beanName，也就是定义bean的id值，主要是做一些缓存的清理和更新，spring缓存机制篇幅也比较多，至此，就完成了spring资源文件的加载和解析。