一个简单的spring hello world：
public class App {

    public static void main(String[] args) {
        ApplicationContext context = new FileSystemXmlApplicationContext("src/main/resources/spring.xml");
        Person person = ((Person) context.getBean("person"));
        person.say();
        person.myBook();
        Book book = ((Book) context.getBean("book"));
        System.out.println(book.toString());
    }

}

首先进入 FileSystemXmlApplicationContext 的构造方法，可以看到该构造方法被重载了，可以传递 configLocation 数组，也就是说，可以传递过个配置文件的地址。默认刷新为true，parent 容器为null。
进入另一个构造器：
	/**
	 * Create a new FileSystemXmlApplicationContext with the given parent,
	 * loading the definitions from the given XML files.
	 * @param configLocations array of file paths
	 * @param refresh whether to automatically refresh the context,
	 * loading all bean definitions and creating all singletons.
	 * Alternatively, call refresh manually after further configuring the context.
	 * @param parent the parent context
	 * @throws BeansException if context creation failed
	 * @see #refresh()
	 */
	public FileSystemXmlApplicationContext(
			String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
			throws BeansException {

		super(parent);
		setConfigLocations(configLocations);
		if (refresh) {
			refresh();
		}
	}
该构造器做了两件事情，一是设置配置文件，二是刷新容器。
其中最重要的就是刷新配置文件refresh()，进入该方法，refresh()方法其实是FileSystemXmlApplicationContext 的父类 AbstractApplicationContext 的refresh()方法。

	@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
            // 为刷新准备应用上下文
			// Prepare this context for refreshing.
			prepareRefresh();

            // 告诉子类刷新内部bean工厂，即在子类中启动refreshBeanFactory()的地方----创建bean工厂，根据配置文件生成bean定义
			// Tell the subclass to refresh the internal bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // 在这个上下文中使用bean工厂
			// Prepare the bean factory for use in this context.
			prepareBeanFactory(beanFactory);

			try {
                // 设置BeanFactory的后置处理器
				// Allows post-processing of the bean factory in context subclasses.
				postProcessBeanFactory(beanFactory);

                // 调用BeanFactory的后处理器，这些后处理器是在Bean定义中向容器注册的
				// Invoke factory processors registered as beans in the context.
				invokeBeanFactoryPostProcessors(beanFactory);

                // 注册Bean的后处理器，在Bean创建过程中调用
				// Register bean processors that intercept bean creation.
				registerBeanPostProcessors(beanFactory);

                //对上下文的消息源进行初始化
				// Initialize message source for this context.
				initMessageSource();

                // 初始化上下文中的事件机制
				// Initialize event multicaster for this context.
				initApplicationEventMulticaster();

                // 初始化其他的特殊Bean
				// Initialize other special beans in specific context subclasses.
				onRefresh();

                // 检查监听Bean并且将这些Bean向容器注册
				// Check for listener beans and register them.
				registerListeners();

                // 实例化所有的（non-lazy-init）单件
				// Instantiate all remaining (non-lazy-init) singletons.
				finishBeanFactoryInitialization(beanFactory);

                //  发布容器事件，结束refresh过程
				// Last step: publish corresponding event.
				finishRefresh();
			}

			catch (BeansException ex) {
				if (logger.isWarnEnabled()) {
					logger.warn("Exception encountered during context initialization - " +
							"cancelling refresh attempt: " + ex);
				}

                // 为防止bean资源占用，在异常处理中，销毁已经在前面过程中生成的单件bean
				// Destroy already created singletons to avoid dangling resources.
				destroyBeans();

                // 重置“active”标志
				// Reset 'active' flag.
				cancelRefresh(ex);

				// Propagate exception to caller.
				throw ex;
			}

			finally {
				// Reset common introspection caches in Spring's core, since we
				// might not ever need metadata for singleton beans anymore...
				resetCommonCaches();
			}
		}
	}
AbstractApplicationContext 的refresh()方法就是整个IOC容器初始化的所有逻辑，该方法大概做了三件事：1、构建BeanFactory 2、构建bean实例并注入相关依赖  3、触发监听

获取BeanFactory


构建BeanFactory就是其中ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();这句代码，也就是AbstractApplicationContext的obtainFreshBeanFactory()方法，从字面上来理解也是获取新的BeanFactory。

AbstractApplicationContext的obtainFreshBeanFactory()方法的第一句代码就是refreshBeanFactory()，refreshBeanFactory()是AbstractApplicationContext的模板方法，进入它的实现AbstractRefreshableApplicationContext里面，其实现代码如下：
	/**
	 * This implementation performs an actual refresh of this context's underlying
	 * bean factory, shutting down the previous bean factory (if any) and
	 * initializing a fresh bean factory for the next phase of the context's lifecycle.
	 */
	@Override
	protected final void refreshBeanFactory() throws BeansException {
		if (hasBeanFactory()) {
            // 如果存在就销毁
			destroyBeans();
			closeBeanFactory();
		}
		try {
            // new DefaultListableBeanFactory(getInternalParentBeanFactory())
			DefaultListableBeanFactory beanFactory = createBeanFactory();
            // 设置序列化
			beanFactory.setSerializationId(getId());
            // 定制的BeanFactory
			customizeBeanFactory(beanFactory);
            // 使用BeanFactory加载bean定义 AbstractXmlApplicationContext
			loadBeanDefinitions(beanFactory);
			synchronized (this.beanFactoryMonitor) {
				this.beanFactory = beanFactory;
			}
		}
		catch (IOException ex) {
			throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
		}
	}
这就是刷新BeanFactory的过程，首先判断是否存在了 BeanFactory，如果存在BeanFactory则销毁，调用 createBeanFactory 方法创建BeanFactory，但是该方法创建的是DefaultListableBeanFactory ，那么也就是说，DefaultListableBeanFactory 就是 BeanFactory的默认实现。

在AbstractRefreshableApplicationContext的refreshBeanFactory()方法中可以看见一句代码：loadBeanDefinitions(beanFactory)，该方法的作用是加载 Definitions，Definition 是spring的核心之一，代表着 IOC 中的基本数据结构。该loadBeanDefinitions(beanFactory)方法也是个抽象方法，默认实现是 AbstractXmlApplicationContext的loadBeanDefinitions(beanFactory)，其代码如下：
	/**
	 * 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);
	}
该方法首先创建一个 XmlBeanDefinitionReader ，用于读取XML中配置，设置了环境、资源加载器，最后初始化，加载。该方法主要是加载BeanDefinition，解析Bean的定义，也就是把xml中定义数据结构转化为 IOC容器中的特定数据结构。
而比较关键的代码则是最后一行的 loadBeanDefinitions(beanDefinitionReader) 方法。
loadBeanDefinitions(beanDefinitionReader) 方法：
	/**
	 * 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) {
            // 加载给定的路径文件
			reader.loadBeanDefinitions(configLocations);
		}
	}
dubug进去看到如图：

configResources 为 null， 表示不会进入第一个语句块，会进入第二个语句块。

loadBeanDefinitions(String... locations) 方法：
	@Override
	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;
	}

该方法的接口介绍：
	/**
     * 从指定的资源位置加载bean定义。
	 * Load bean definitions from the specified resource locations.
	 * @param locations the resource locations, to be loaded with the ResourceLoader
	 * (or ResourcePatternResolver) of this bean definition reader
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException in case of loading or parsing errors
	 */
	int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException;

该loadBeanDefinitions(String... locations) 方法的核心逻辑是for循环中的 loadBeanDefinitions(location); 该代码最后调用AbstractBeanDefinitionReader.loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources)方法。

loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) 方法 ：

	/**
	 * Load bean definitions from the specified resource location.
	 * <p>The location can also be a location pattern, provided that the
	 * ResourceLoader of this bean definition reader is a ResourcePatternResolver.
	 * @param location the resource location, to be loaded with the ResourceLoader
	 * (or ResourcePatternResolver) of this bean definition reader
	 * @param actualResources a Set to be filled with the actual Resource objects
	 * that have been resolved during the loading process. May be {@code null}
	 * to indicate that the caller is not interested in those Resource objects.
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException in case of loading or parsing errors
	 * @see #getResourceLoader()
	 * @see #loadBeanDefinitions(org.springframework.core.io.Resource)
	 * @see #loadBeanDefinitions(org.springframework.core.io.Resource[])
	 */
	public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
        // 获取资源加载器 
		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 {
                // 获取资源数组
				Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
                // 根据配置文件加载bean definitions
				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;
		}
	}


如上图：该方法首先获取资源加载器，然后进入 if 块，获取资源数组，调用 loadBeanDefinitions(resources) ，根据配置文件加载Bean定义。

主要看看 loadBeanDefinitions(resources)  的实现，

loadBeanDefinitions(Resource... resources) 方法 ：
	@Override
	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;
	}
该方法主要在循环加载resource 资源数组，看看其加载resource 资源数组的实现 -- int loadBeanDefinitions(Resource resource) 接口， 进入该接口的 XmlBeanDefinitionReader 实现，该实现方法会调用loadBeanDefinitions(EncodedResource encodedResource)方法。

该loadBeanDefinitions(EncodedResource encodedResource)方法主要调用doLoadBeanDefinitions(inputSource, encodedResource.getResource());方法
doLoadBeanDefinitions(InputSource inputSource, Resource resource)方法：
	/**
	 * 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 {
			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);
		}
	}

该方法主要做两件事：
1、根据输入流加载 Document 文档对象
2、根据得到的文档对象注册到容器

看看 根据得到的文档对象注册到容器 的实现：
registerBeanDefinitions(Document doc, Resource resource)方法：
	/**
	 * 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 {
        // 创建一个 BeanDefinitionDocumentReader， 用于读取 BeanDefinition
		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
		int countBefore = getRegistry().getBeanDefinitionCount();
		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
		return getRegistry().getBeanDefinitionCount() - countBefore;
	}

其中documentReader调用registerBeanDefinitions(doc, createReaderContext(resource));，

registerBeanDefinitions(Document doc, XmlReaderContext readerContext) 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) {
		this.readerContext = readerContext;
		logger.debug("Loading bean definitions");
		Element root = doc.getDocumentElement();
		doRegisterBeanDefinitions(root);
	}
该方法从文档对象Document中获取根元素，最后调用 DefaultBeanDefinitionDocumentReader.doRegisterBeanDefinitions(root) 进行注册。

该doRegisterBeanDefinitions(Element root)方法：
	/**
	 * Register each bean definition within the given root {@code <beans/>} element.
	 */
	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);
				if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
					if (logger.isInfoEnabled()) {
						logger.info("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;
	}
该方法最重要的是倒数第三行的：parseBeanDefinitions(root, this.delegate);

parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate)方法：
	/**
	 * 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);
		}
	}
该方法就是一个解析XML 文档的步骤，核心是调用 parseDefaultElement(ele, delegate)
而 parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) 方法主要是调用processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate)方法

processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate)方法:
	/**
	 * Process the given bean element, parsing the bean definition
	 * and registering it with the registry.
	 */
	protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        // 创建一个 BeanDefinitionHolder
		BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
		if (bdHolder != null) {
			bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
			try {
				// Register the final decorated instance.
                // 执行容器通知事件
				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));
		}
	}

其中，该静态方法registerBeanDefinition(BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)：
	/**
	 * 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.
        // 从bean的持有者那里获取了beanName
		String beanName = definitionHolder.getBeanName();
        // 将bena的名字和 BeanDefinition 注册
		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);
			}
		}
	}

其注册接口registerBeanDefinition(String beanName, BeanDefinition beanDefinition)的DefaultListableBeanFactory类的实现：
	@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 {
				((AbstractBeanDefinition) beanDefinition).validate();
			}
			catch (BeanDefinitionValidationException ex) {
				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Validation of bean definition failed", ex);
			}
		}

		BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
		if (existingDefinition != null) {
			if (!isAllowBeanDefinitionOverriding()) {
				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
						"': There is already [" + existingDefinition + "] bound.");
			}
			else if (existingDefinition.getRole() < beanDefinition.getRole()) {
				// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
				if (logger.isWarnEnabled()) {
					logger.warn("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.isInfoEnabled()) {
					logger.info("Overriding bean definition for bean '" + beanName +
							"' with a different definition: replacing [" + existingDefinition +
							"] with [" + beanDefinition + "]");
				}
			}
			else {
				if (logger.isDebugEnabled()) {
					logger.debug("Overriding bean definition for bean '" + beanName +
							"' with an equivalent definition: replacing [" + existingDefinition +
							"] with [" + beanDefinition + "]");
				}
			}
			this.beanDefinitionMap.put(beanName, beanDefinition);
		}
		else {
			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 {
				// Still in startup registration phase -- 最终放进这个map 实现注册
				this.beanDefinitionMap.put(beanName, beanDefinition);// 走这里 // private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);
				this.beanDefinitionNames.add(beanName);
				this.manualSingletonNames.remove(beanName);
			}
			this.frozenBeanDefinitionNames = null;
		}

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

该方法可以说是注册bean的最后一步，将beanName和 beanDefinition 放进一个 ConcurrentHashMap（256） 中。


前面忽略了beanDefinition 的创建，beanDefinition 是在DefaultBeanDefinitionDocumentReader.processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) 方法中，在这里创建了 BeanDefinitionHolder， 而创建了 BeanDefinitionHolder实例中解析Bean并将Bean 保存在该对象中。

该实例会调用 parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) 方法，该方法用于解析XML文件并创建一个 BeanDefinitionHolder 返回，该方法会调用 parseBeanDefinitionElement(ele, beanName, containingBean) 方法， 我们看看该方法：
	/**
	 * 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;
		if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
            // 类全限定名称
			className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
		}
		String parent = null;
		if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
			parent = ele.getAttribute(PARENT_ATTRIBUTE);
		}

		try {
            // 创建
			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;
	}

该方法从XML元素中取出 class 元素，然后拿着className调用 createBeanDefinition(className, parent) 方法，该方法核心是调用 BeanDefinitionReaderUtils.createBeanDefinition 方法，我们看看该方法：

	/**
	 * 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(
			@Nullable String parentName, @Nullable String className, @Nullable ClassLoader classLoader) throws ClassNotFoundException {

        // 泛型的bean定义，也就是最终生成的bean定义。
		GenericBeanDefinition bd = new GenericBeanDefinition();
		bd.setParentName(parentName);
		if (className != null) {
			if (classLoader != null) {
                // 设置Class 对象
				bd.setBeanClass(ClassUtils.forName(className, classLoader));
			}
			else {
				bd.setBeanClassName(className);
			}
		}
		return bd;
	}

该方法创建一个 Definition 的持有者，然后设置该持有者的Class对象，该对象就是我们在配置文件中配置的Class对象。最后返回。

#############创建Bean实例并构建Bean的依赖关系网###########################################
我们刚刚创建了Bean工厂，并创建 BeanDefinitions 放进Map里，以beanName为key。那么我们现在有了Bean定义，但还没有实例，也没有构建Bean与Bean之间的依赖关系。

我们知道，构建依赖关系是 IOC 的一个重要的任务，我们怎么能放过。那么是在哪里做的呢？在 refresh() 方法的finishBeanFactoryInitialization(beanFactory) 方法中。该方法中重要的一步是 ： beanFactory.preInstantiateSingletons()，我们有必要看看该方法实现：

	@Override
	public void preInstantiateSingletons() throws BeansException {
		if (logger.isDebugEnabled()) {
			logger.debug("Pre-instantiating singletons in " + this);
		}

		// Iterate over a copy to allow for init methods which in turn register new bean definitions.
		// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
		List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

		// Trigger initialization of all non-lazy singleton beans...
		for (String beanName : beanNames) {
			RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
			if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
				if (isFactoryBean(beanName)) {
					Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
					if (bean instanceof FactoryBean) {
						final FactoryBean<?> factory = (FactoryBean<?>) bean;
						boolean isEagerInit;
						if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
							isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>)
											((SmartFactoryBean<?>) factory)::isEagerInit,
									getAccessControlContext());
						}
						else {
							isEagerInit = (factory instanceof SmartFactoryBean &&
									((SmartFactoryBean<?>) factory).isEagerInit());
						}
						if (isEagerInit) {
							getBean(beanName);
						}
					}
				}
				else {
					getBean(beanName);
				}
			}
		}

		// Trigger post-initialization callback for all applicable beans...
		for (String beanName : beanNames) {
			Object singletonInstance = getSingleton(beanName);
			if (singletonInstance instanceof SmartInitializingSingleton) {
				final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
				if (System.getSecurityManager() != null) {
					AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
						smartSingleton.afterSingletonsInstantiated();
						return null;
					}, getAccessControlContext());
				}
				else {
					smartSingleton.afterSingletonsInstantiated();
				}
			}
		}
	}


该方法首先循环所有的BeanNames，并且调用getBean(beanName);方法，该方法实际上就是创建bean并递归构建依赖关系。该方法会调用 doGetBean(name, null, null, false)，我们进入该方法查看，该方法很长，楼主挑选重要代码：


	/**
	 * Return an instance, which may be shared or independent, of the specified bean.
	 * @param name the name of the bean to retrieve
	 * @param requiredType the required type of the bean to retrieve
	 * @param args arguments to use when creating a bean instance using explicit arguments
	 * (only applied when creating a new instance as opposed to retrieving an existing one)
	 * @param typeCheckOnly whether the instance is obtained for a type check,
	 * not for actual use
	 * @return an instance of the bean
	 * @throws BeansException if the bean could not be created
	 */
	@SuppressWarnings("unchecked")
	protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
			@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {

		final String beanName = transformedBeanName(name);
		Object bean;

		// Eagerly check singleton cache for manually registered singletons.
		Object sharedInstance = getSingleton(beanName);
		if (sharedInstance != null && args == null) {
			if (logger.isDebugEnabled()) {
				if (isSingletonCurrentlyInCreation(beanName)) {
					logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
							"' that is not fully initialized yet - a consequence of a circular reference");
				}
				else {
					logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
				}
			}
			bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
		}

		else {
			// Fail if we're already creating this bean instance:
			// We're assumably within a circular reference.
			if (isPrototypeCurrentlyInCreation(beanName)) {
				throw new BeanCurrentlyInCreationException(beanName);
			}

			// Check if bean definition exists in this factory.
			BeanFactory parentBeanFactory = getParentBeanFactory();
			if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
				// Not found -> check parent.
				String nameToLookup = originalBeanName(name);
				if (parentBeanFactory instanceof AbstractBeanFactory) {
					return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
							nameToLookup, requiredType, args, typeCheckOnly);
				}
				else if (args != null) {
					// Delegation to parent with explicit args.
					return (T) parentBeanFactory.getBean(nameToLookup, args);
				}
				else {
					// No args -> delegate to standard getBean method.
					return parentBeanFactory.getBean(nameToLookup, requiredType);
				}
			}

			if (!typeCheckOnly) {
				markBeanAsCreated(beanName);
			}

			try {
				final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
				checkMergedBeanDefinition(mbd, beanName, args);

				// Guarantee initialization of beans that the current bean depends on.
				String[] dependsOn = mbd.getDependsOn();
				if (dependsOn != null) {
					for (String dep : dependsOn) {
						if (isDependent(beanName, dep)) {
							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
									"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
						}
						registerDependentBean(dep, beanName);
						try {
							getBean(dep);
						}
						catch (NoSuchBeanDefinitionException ex) {
							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
									"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
						}
					}
				}

				// Create bean instance.
				if (mbd.isSingleton()) {
					sharedInstance = getSingleton(beanName, () -> {
						try {
							return createBean(beanName, mbd, args);
						}
						catch (BeansException ex) {
							// Explicitly remove instance from singleton cache: It might have been put there
							// eagerly by the creation process, to allow for circular reference resolution.
							// Also remove any beans that received a temporary reference to the bean.
							destroySingleton(beanName);
							throw ex;
						}
					});
					bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
				}

				else if (mbd.isPrototype()) {
					// It's a prototype -> create a new instance.
					Object prototypeInstance = null;
					try {
						beforePrototypeCreation(beanName);
						prototypeInstance = createBean(beanName, mbd, args);
					}
					finally {
						afterPrototypeCreation(beanName);
					}
					bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
				}

				else {
					String scopeName = mbd.getScope();
					final Scope scope = this.scopes.get(scopeName);
					if (scope == null) {
						throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
					}
					try {
						Object scopedInstance = scope.get(beanName, () -> {
							beforePrototypeCreation(beanName);
							try {
								return createBean(beanName, mbd, args);
							}
							finally {
								afterPrototypeCreation(beanName);
							}
						});
						bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
					}
					catch (IllegalStateException ex) {
						throw new BeanCreationException(beanName,
								"Scope '" + scopeName + "' is not active for the current thread; consider " +
								"defining a scoped proxy for this bean if you intend to refer to it from a singleton",
								ex);
					}
				}
			}
			catch (BeansException ex) {
				cleanupAfterBeanCreationFailure(beanName);
				throw ex;
			}
		}

		// Check if required type matches the type of the actual bean instance.
		if (requiredType != null && !requiredType.isInstance(bean)) {
			try {
				T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
				if (convertedBean == null) {
					throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
				}
				return convertedBean;
			}
			catch (TypeMismatchException ex) {
				if (logger.isDebugEnabled()) {
					logger.debug("Failed to convert bean '" + name + "' to required type '" +
							ClassUtils.getQualifiedName(requiredType) + "'", ex);
				}
				throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
			}
		}
		return (T) bean;
	}


其中部分重要代码截图：


可以看到，该方法首先会获取依赖关系，拿着依赖的BeanName 递归调用 getBean方法，直到调用 getSingleton 方法返回依赖bean，而 getSingleton 方法的参数是 createBean 返回的实例，该createBean 方法内部调用 AbstractAutowireCapableBeanFactory.doCreateBean 方法：

	/**
	 * Actually create the specified bean. Pre-creation processing has already happened
	 * at this point, e.g. checking {@code postProcessBeforeInstantiation} callbacks.
	 * <p>Differentiates between default bean instantiation, use of a
	 * factory method, and autowiring a constructor.
	 * @param beanName the name of the bean
	 * @param mbd the merged bean definition for the bean
	 * @param args explicit arguments to use for constructor or factory method invocation
	 * @return a new instance of the bean
	 * @throws BeanCreationException if the bean could not be created
	 * @see #instantiateBean
	 * @see #instantiateUsingFactoryMethod
	 * @see #autowireConstructor
	 */
	protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
			throws BeanCreationException {

		// Instantiate the bean.
		BeanWrapper instanceWrapper = null;
		if (mbd.isSingleton()) {
			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
		}
		if (instanceWrapper == null) {
			instanceWrapper = createBeanInstance(beanName, mbd, args);
		}
		final Object bean = instanceWrapper.getWrappedInstance();
		Class<?> beanType = instanceWrapper.getWrappedClass();
		if (beanType != NullBean.class) {
			mbd.resolvedTargetType = beanType;
		}

		// Allow post-processors to modify the merged bean definition.
		synchronized (mbd.postProcessingLock) {
			if (!mbd.postProcessed) {
				try {
					applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
				}
				catch (Throwable ex) {
					throw new BeanCreationException(mbd.getResourceDescription(), beanName,
							"Post-processing of merged bean definition failed", ex);
				}
				mbd.postProcessed = true;
			}
		}

		// Eagerly cache singletons to be able to resolve circular references
		// even when triggered by lifecycle interfaces like BeanFactoryAware.
		boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
				isSingletonCurrentlyInCreation(beanName));
		if (earlySingletonExposure) {
			if (logger.isDebugEnabled()) {
				logger.debug("Eagerly caching bean '" + beanName +
						"' to allow for resolving potential circular references");
			}
			addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
		}

		// Initialize the bean instance.
		Object exposedObject = bean;
		try {
			populateBean(beanName, mbd, instanceWrapper);
			exposedObject = initializeBean(beanName, exposedObject, mbd);
		}
		catch (Throwable ex) {
			if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
				throw (BeanCreationException) ex;
			}
			else {
				throw new BeanCreationException(
						mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
			}
		}

		if (earlySingletonExposure) {
			Object earlySingletonReference = getSingleton(beanName, false);
			if (earlySingletonReference != null) {
				if (exposedObject == bean) {
					exposedObject = earlySingletonReference;
				}
				else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
					String[] dependentBeans = getDependentBeans(beanName);
					Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
					for (String dependentBean : dependentBeans) {
						if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
							actualDependentBeans.add(dependentBean);
						}
					}
					if (!actualDependentBeans.isEmpty()) {
						throw new BeanCurrentlyInCreationException(beanName,
								"Bean with name '" + beanName + "' has been injected into other beans [" +
								StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
								"] in its raw version as part of a circular reference, but has eventually been " +
								"wrapped. This means that said other beans do not use the final version of the " +
								"bean. This is often the result of over-eager type matching - consider using " +
								"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
					}
				}
			}
		}

		// Register bean as disposable.
		try {
			registerDisposableBeanIfNecessary(beanName, bean, mbd);
		}
		catch (BeanDefinitionValidationException ex) {
			throw new BeanCreationException(
					mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
		}

		return exposedObject;
	}


该方法很长，我们重点关注以下2行代码：

instanceWrapper = createBeanInstance(beanName, mbd, args) 创建实例。
populateBean(beanName, mbd, instanceWrapper) ， 该方法用于填充Bean，该
方法可以就是说就是发生依赖注入的地方。

createBeanInstance(beanName, mbd, args):
	/**
	 * Create a new instance for the specified bean, using an appropriate instantiation strategy:
	 * factory method, constructor autowiring, or simple instantiation.
	 * @param beanName the name of the bean
	 * @param mbd the bean definition for the bean
	 * @param args explicit arguments to use for constructor or factory method invocation
	 * @return a BeanWrapper for the new instance
	 * @see #obtainFromSupplier
	 * @see #instantiateUsingFactoryMethod
	 * @see #autowireConstructor
	 * @see #instantiateBean
	 */
	protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
		// Make sure bean class is actually resolved at this point.
		Class<?> beanClass = resolveBeanClass(mbd, beanName);

		if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
			throw new BeanCreationException(mbd.getResourceDescription(), beanName,
					"Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
		}

		Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
		if (instanceSupplier != null) {
			return obtainFromSupplier(instanceSupplier, beanName);
		}

		if (mbd.getFactoryMethodName() != null)  {
			return instantiateUsingFactoryMethod(beanName, mbd, args);
		}

		// Shortcut when re-creating the same bean...
		boolean resolved = false;
		boolean autowireNecessary = false;
		if (args == null) {
			synchronized (mbd.constructorArgumentLock) {
				if (mbd.resolvedConstructorOrFactoryMethod != null) {
					resolved = true;
					autowireNecessary = mbd.constructorArgumentsResolved;
				}
			}
		}
		if (resolved) {
			if (autowireNecessary) {
				return autowireConstructor(beanName, mbd, null, null);
			}
			else {
				return instantiateBean(beanName, mbd);
			}
		}

		// Need to determine the constructor...
		Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
		if (ctors != null ||
				mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
				mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args))  {
			return autowireConstructor(beanName, mbd, ctors, args);
		}

		// No special handling: simply use no-arg constructor.
		return instantiateBean(beanName, mbd);
	}

该方法的doc注释是这样介绍的：为指定的bean创建一个新的实例，使用适当的实例化策略:工厂方法、构造函数自动装配或简单实例化。

我们看，该方法首先创建Class 对象，然后获取构造器对象，最后调用 instantiateBean(beanName, mbd) 方法，
 instantiateBean(beanName, mbd) 方法实现：
	/**
	 * Instantiate the given bean using its default constructor.
	 * @param beanName the name of the bean
	 * @param mbd the bean definition for the bean
	 * @return a BeanWrapper for the new instance
	 */
	protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
		try {
			Object beanInstance;
			final BeanFactory parent = this;
			if (System.getSecurityManager() != null) {
				beanInstance = AccessController.doPrivileged((PrivilegedAction<Object>) () ->
						getInstantiationStrategy().instantiate(mbd, beanName, parent),
						getAccessControlContext());
			}
			else {
				beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
			}
			BeanWrapper bw = new BeanWrapperImpl(beanInstance);
			initBeanWrapper(bw);
			return bw;
		}
		catch (Throwable ex) {
			throw new BeanCreationException(
					mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
		}
	}

该方法核心逻辑是 beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent)，携带BeanName ,RootBeanDefinition ,发挥的策略对象是 SimpleInstantiationStrategy，该方法内部调用静态方法 BeanUtils.instantiateClass(constructorToUse)， 组后调用 Constructor 的 newInstance 方法， 也就是最终使用反射创建了该实例：

	/**
	 * Convenience method to instantiate a class using the given constructor.
	 * <p>Note that this method tries to set the constructor accessible if given a
	 * non-accessible (that is, non-public) constructor, and supports Kotlin classes
	 * with optional parameters and default values.
	 * @param ctor the constructor to instantiate
	 * @param args the constructor arguments to apply (use {@code null} for an unspecified
	 * parameter if needed for Kotlin classes with optional parameters and default values)
	 * @return the new instance
	 * @throws BeanInstantiationException if the bean cannot be instantiated
	 * @see Constructor#newInstance
	 */
	public static <T> T instantiateClass(Constructor<T> ctor, Object... args) throws BeanInstantiationException {
		Assert.notNull(ctor, "Constructor must not be null");
		try {
			ReflectionUtils.makeAccessible(ctor);
			return (KotlinDetector.isKotlinType(ctor.getDeclaringClass()) ?
					KotlinDelegate.instantiateClass(ctor, args) : ctor.newInstance(args));
		}
		catch (InstantiationException ex) {
			throw new BeanInstantiationException(ctor, "Is it an abstract class?", ex);
		}
		catch (IllegalAccessException ex) {
			throw new BeanInstantiationException(ctor, "Is the constructor accessible?", ex);
		}
		catch (IllegalArgumentException ex) {
			throw new BeanInstantiationException(ctor, "Illegal arguments for constructor", ex);
		}
		catch (InvocationTargetException ex) {
			throw new BeanInstantiationException(ctor, "Constructor threw exception", ex.getTargetException());
		}
	}


该方法会判断是否是 Kotlin 类型。如果不是，则调用构造器的实例方法。
到这里，我们的实例已经创建。但是我们的实例的依赖还没有设置，刚刚我们在 doCreateBean方法说关心以下2行代码：

instanceWrapper = createBeanInstance(beanName, mbd, args) 创建实例。
populateBean(beanName, mbd, instanceWrapper) ， 该方法用于填充Bean，该方法可以就是说就是发生依赖注入的地方。
我们已经解析了第一个，现在看第二个方法：
	/**
	 * Populate the bean instance in the given BeanWrapper with the property values
	 * from the bean definition.
	 * @param beanName the name of the bean
	 * @param mbd the bean definition for the bean
	 * @param bw the BeanWrapper with bean instance
	 */
	protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
		if (bw == null) {
			if (mbd.hasPropertyValues()) {
				throw new BeanCreationException(
						mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
			}
			else {
				// Skip property population phase for null instance.
				return;
			}
		}

		// Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
		// state of the bean before properties are set. This can be used, for example,
		// to support styles of field injection.
		boolean continueWithPropertyPopulation = true;

		if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				if (bp instanceof InstantiationAwareBeanPostProcessor) {
					InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
					if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
						continueWithPropertyPopulation = false;
						break;
					}
				}
			}
		}

		if (!continueWithPropertyPopulation) {
			return;
		}

		PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);

		if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
				mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
			MutablePropertyValues newPvs = new MutablePropertyValues(pvs);

			// Add property values based on autowire by name if applicable.
			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
				autowireByName(beanName, mbd, bw, newPvs);
			}

			// Add property values based on autowire by type if applicable.
			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
				autowireByType(beanName, mbd, bw, newPvs);
			}

			pvs = newPvs;
		}

		boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
		boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);

		if (hasInstAwareBpps || needsDepCheck) {
			if (pvs == null) {
				pvs = mbd.getPropertyValues();
			}
			PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
			if (hasInstAwareBpps) {
				for (BeanPostProcessor bp : getBeanPostProcessors()) {
					if (bp instanceof InstantiationAwareBeanPostProcessor) {
						InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
						pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
						if (pvs == null) {
							return;
						}
					}
				}
			}
			if (needsDepCheck) {
				checkDependencies(beanName, mbd, filteredPds, pvs);
			}
		}

		if (pvs != null) {
			applyPropertyValues(beanName, mbd, bw, pvs);
		}
	}


该方法核心逻辑是
 PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null)， 

即获取该bean的所有属性，也就是我们配置property元素。最后执行 applyPropertyValues(beanName, mbd, bw, pvs) 方法。


	/**
	 * Apply the given property values, resolving any runtime references
	 * to other beans in this bean factory. Must use deep copy, so we
	 * don't permanently modify this property.
	 * @param beanName the bean name passed for better exception information
	 * @param mbd the merged bean definition
	 * @param bw the BeanWrapper wrapping the target object
	 * @param pvs the new property values
	 */
	protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
		if (pvs.isEmpty()) {
			return;
		}

		if (System.getSecurityManager() != null && bw instanceof BeanWrapperImpl) {
			((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext());
		}

		MutablePropertyValues mpvs = null;
		List<PropertyValue> original;

		if (pvs instanceof MutablePropertyValues) {
			mpvs = (MutablePropertyValues) pvs;
			if (mpvs.isConverted()) {
				// Shortcut: use the pre-converted values as-is.
				try {
					bw.setPropertyValues(mpvs);
					return;
				}
				catch (BeansException ex) {
					throw new BeanCreationException(
							mbd.getResourceDescription(), beanName, "Error setting property values", ex);
				}
			}
			original = mpvs.getPropertyValueList();
		}
		else {
			original = Arrays.asList(pvs.getPropertyValues());
		}

		TypeConverter converter = getCustomTypeConverter();
		if (converter == null) {
			converter = bw;
		}
		BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);

		// Create a deep copy, resolving any references for values.
		List<PropertyValue> deepCopy = new ArrayList<>(original.size());
		boolean resolveNecessary = false;
		for (PropertyValue pv : original) {
			if (pv.isConverted()) {
				deepCopy.add(pv);
			}
			else {
				String propertyName = pv.getName();
				Object originalValue = pv.getValue();
				Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
				Object convertedValue = resolvedValue;
				boolean convertible = bw.isWritableProperty(propertyName) &&
						!PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
				if (convertible) {
					convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
				}
				// Possibly store converted value in merged bean definition,
				// in order to avoid re-conversion for every created bean instance.
				if (resolvedValue == originalValue) {
					if (convertible) {
						pv.setConvertedValue(convertedValue);
					}
					deepCopy.add(pv);
				}
				else if (convertible && originalValue instanceof TypedStringValue &&
						!((TypedStringValue) originalValue).isDynamic() &&
						!(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) {
					pv.setConvertedValue(convertedValue);
					deepCopy.add(pv);
				}
				else {
					resolveNecessary = true;
					deepCopy.add(new PropertyValue(pv, convertedValue));
				}
			}
		}
		if (mpvs != null && !resolveNecessary) {
			mpvs.setConverted();
		}

		// Set our (possibly massaged) deep copy.
		try {
			bw.setPropertyValues(new MutablePropertyValues(deepCopy));
		}
		catch (BeansException ex) {
			throw new BeanCreationException(
					mbd.getResourceDescription(), beanName, "Error setting property values", ex);
		}
	}


注意，现在的PropertyValues 都是字符串，没有值的，这个方法的作用就是获取值，关键代码：
Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue)

该方法会获取 pvName 所对应的容器value，该方法内部会调用 BeanWrapperImpl的resolveReference(argName, ref) 方法，我们看看该方法：

	/**
	 * Resolve a reference to another bean in the factory.
	 */
	@Nullable
	private Object resolveReference(Object argName, RuntimeBeanReference ref) {
		try {
			Object bean;
			String refName = ref.getBeanName();
			refName = String.valueOf(doEvaluate(refName));
			if (ref.isToParent()) {
				if (this.beanFactory.getParentBeanFactory() == null) {
					throw new BeanCreationException(
							this.beanDefinition.getResourceDescription(), this.beanName,
							"Can't resolve reference to bean '" + refName +
							"' in parent factory: no parent factory available");
				}
				bean = this.beanFactory.getParentBeanFactory().getBean(refName);
			}
			else {
				bean = this.beanFactory.getBean(refName);
				this.beanFactory.registerDependentBean(refName, this.beanName);
			}
			if (bean instanceof NullBean) {
				bean = null;
			}
			return bean;
		}
		catch (BeansException ex) {
			throw new BeanCreationException(
					this.beanDefinition.getResourceDescription(), this.beanName,
					"Cannot resolve reference to bean '" + ref.getBeanName() + "' while setting " + argName, ex);
		}
	}

其中有一行熟悉的代码：bean = this.beanFactory.getBean(refName)，对，这里就是发生递归的地方。该方法会拿着属性名称从容器中获取实例。

我们回到 applyPropertyValues 方法。此时deepCopy 集合已经有值了，不再仅仅是字符串了。

然后调用 setPropertyValues(new MutablePropertyValues(deepCopy)) 方法， 该方法会调用 AbstractPropertyAccessor.setPropertyValues 方法完成注入，而该方法会循环元素列表， 循环中调用 setPropertyValue(PropertyValue pv) 方法， 该方法setPropertyValue(PropertyValue pv)最后会调用 nestedPa.setPropertyValue(tokens, pv) 方法， 该方法又会调用 processLocalProperty(tokens, pv) 方法，该方法最后又会调用 ph.setValue(valueToApply) 方法，也就是BeanWrapperImpl.setValue() 方法，终于，我们要看到反射了，看到反射说明到了尽头。

		@Override
		public void setValue(final @Nullable Object value) throws Exception {
			final Method writeMethod = (this.pd instanceof GenericTypeAwarePropertyDescriptor ?
					((GenericTypeAwarePropertyDescriptor) this.pd).getWriteMethodForActualAccess() :
					this.pd.getWriteMethod());
			if (System.getSecurityManager() != null) {
				AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
					ReflectionUtils.makeAccessible(writeMethod);
					return null;
				});
				try {
					AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () ->
							writeMethod.invoke(getWrappedInstance(), value), acc);
				}
				catch (PrivilegedActionException ex) {
					throw ex.getException();
				}
			}
			else {
				ReflectionUtils.makeAccessible(writeMethod);
				writeMethod.invoke(getWrappedInstance(), value);
			}
		}
	}