彻底弄懂Spring中Bean的解析、创建和使用

ApplicationContext context = new ClassPathXmlApplicationContext("classpath:/spring/test.xml");

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
       ">
    <bean id="stringutil" class="com.baigt.utils.StringUtils"></bean>
</beans>

public class StringUtils{
// some code
}

	public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
		this(new String[] {configLocation}, true, null);
	}
	// 省略some code 
	
	public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
		throws BeansException {

	super(parent);
	//当前ClassPathXmlApplicationContext也是resource的子类
	setConfigLocations(configLocations);
	//前边传入的refresh为true，执行 refresh方法
	if (refresh) {
		refresh();
	}
}

	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// refresh的前置准备，比如设置startTime，开启激活状态、关闭close状态等等等
			prepareRefresh();

			//告诉子类去刷新内容Bean工厂(从类图中可以明显看出来入口类实例也是个bean工厂)
			// 观察和刷新BeanFactory
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			//提前设置一些在该context中使用的属性，比如Classloader、Callback、environment等
			prepareBeanFactory(beanFactory);

			try {
				// 通知context子类，后置处理beanFactory。比如用一系列的Webcontext子类
				postProcessBeanFactory(beanFactory);

				// 将BeanFactoryPostProcessor在当前Context中注册为Bean
				invokeBeanFactoryPostProcessors(beanFactory);

				// 注册BeanPostProcessor来拦截Bean创建的后置处理。
				registerBeanPostProcessors(beanFactory);

				// 为当前Context初始化MessageSource
				initMessageSource();

				// 为当前context初始化应用事件广播
				initApplicationEventMulticaster();

				// 初始化其他特殊的bean对象 比如webcontext
				onRefresh();

				// 检查监听Bean 并发布他们(ApplicationListener)
				registerListeners();

				// 实例化BeanFactory中所有的其他的单例对象集合(非延迟的)
				finishBeanFactoryInitialization(beanFactory);

				// 最后发布LifecycleProcessor和ContextRefreshedEvent事件
				finishRefresh();
			}

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

				// 失败销毁bean
				destroyBeans();

				// 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();
			}
		}
	}

<li>BeanNameAware's {@code setBeanName}
 * <li>BeanClassLoaderAware's {@code setBeanClassLoader}
 * <li>BeanFactoryAware's {@code setBeanFactory}
 * <li>EnvironmentAware's {@code setEnvironment}
 * <li>EmbeddedValueResolverAware's {@code setEmbeddedValueResolver}
 * <li>ResourceLoaderAware's {@code setResourceLoader}
 * (only applicable when running in an application context)
 * <li>ApplicationEventPublisherAware's {@code setApplicationEventPublisher}
 * (only applicable when running in an application context)
 * <li>MessageSourceAware's {@code setMessageSource}
 * (only applicable when running in an application context)
 * <li>ApplicationContextAware's {@code setApplicationContext}
 * (only applicable when running in an application context)
 * <li>ServletContextAware's {@code setServletContext}
 * (only applicable when running in a web application context)
 * <li>{@code postProcessBeforeInitialization} methods of BeanPostProcessors
 * <li>InitializingBean's {@code afterPropertiesSet}
 * <li>a custom init-method definition
 * <li>{@code postProcessAfterInitialization} methods of BeanPostProcessors
 * </ol>
 *
 * <p>On shutdown of a bean factory, the following lifecycle methods apply:
 * <ol>
 * <li>{@code postProcessBeforeDestruction} methods of DestructionAwareBeanPostProcessors
 * <li>DisposableBean's {@code destroy}
 * <li>a custom destroy-method definition

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
		// 如果已经有了工厂直接销毁，然后再建工厂
		refreshBeanFactory();
		//基本是从上边创建的beanFactory拿的
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		if (logger.isDebugEnabled()) {
			logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
		}
		return beanFactory;
	}

	protected final void refreshBeanFactory() throws BeansException {
		//如果有bean工厂销毁bean，关闭bean工厂
		if (hasBeanFactory()) {
			destroyBeans();
			closeBeanFactory();
		}
		try {
			//创建 DefaultListableBeanFactory  而此工厂是BeanDefinitionRegistry的一个子类
			DefaultListableBeanFactory beanFactory = createBeanFactory();
			beanFactory.setSerializationId(getId());
			customizeBeanFactory(beanFactory);
			//加载BeanDefinition(该例中是解析Xml中的Bean标签，并装载到BeanDefinition中)
			loadBeanDefinitions(beanFactory);
			synchronized (this.beanFactoryMonitor) {
				//赋值给Context中的beanFactory
				this.beanFactory = beanFactory;
			}
		}
		catch (IOException ex) {
			
		}
	}

	protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
		// 使用给定的beanFactory(BeanDefinitionRegistry) 来创建XmlBeanDefinitionReader实例
		XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

		// Configure the bean definition reader with this context's
		// resource loading environment.
		beanDefinitionReader.setEnvironment(this.getEnvironment());
		// ClassPathXmlApplicationContext也是一个ResouceLoader
		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);
		// 通过XmlBeanDefinitionReader解析生成BeanDefinition
		loadBeanDefinitions(beanDefinitionReader);
	}
	
	//接上
	protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
		Resource[] configResources = getConfigResources();
		if (configResources != null) {
			reader.loadBeanDefinitions(configResources);
		}
		// 入口中传入的test.xml被存放在this.configLocations上，这里可以拿到。
		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 counter = 0;
		for (String location : locations) {
			counter += loadBeanDefinitions(location);
		}
		return counter;
	}

	//接上
		public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {
		return loadBeanDefinitions(location, null);
	}
	// 接上  
	// 从类图中可知 this对象(ClassPathXmlApplicationContext) 也是DefaultResourceLoader实例，已经被set进reader中,所以走else逻辑
	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 {
			// 只能加载从绝对路径加载单resouce   location为我们传入的test.xml 路径
			Resource resource = resourceLoader.getResource(location);
			//我们再继续跟进!!!
			int loadCount = loadBeanDefinitions(resource);
			if (actualResources != null) {
				actualResources.add(resource);
			}
			if (logger.isDebugEnabled()) {
				logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
			}
			return loadCount;
		}
	}

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

	public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
		//... 省略代码
		try {
			// 前边我们传入的test.xml的输入流
			InputStream inputStream = encodedResource.getResource().getInputStream();
			try {
				InputSource inputSource = new InputSource(inputStream);
				if (encodedResource.getEncoding() != null) {
					inputSource.setEncoding(encodedResource.getEncoding());
				}
				//真正的从xml中load bean definition
				return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
			}
			finally {
				inputStream.close();
			}
		}
		catch (IOException ex) {
			
		}
	}

// 接上
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
			throws BeanDefinitionStoreException {
		try {
			// 解析xml文件为Document
			Document doc = doLoadDocument(inputSource, resource);
			return registerBeanDefinitions(doc, resource);
		}
		catch (BeanDefinitionStoreException ex) {
			// 省略代码
		}
	}
// 接上
	public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
		int countBefore = getRegistry().getBeanDefinitionCount();
		// 从reader中注册BeanDefinition到工厂
		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
		return getRegistry().getBeanDefinitionCount() - countBefore;
	}

	public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
		this.readerContext = readerContext;
		logger.debug("Loading bean definitions");
		Element root = doc.getDocumentElement();
		doRegisterBeanDefinitions(root);
	}
	// 接上  通过委托模式和模板模式来解析xml   
	protected void doRegisterBeanDefinitions(Element root) {
		BeanDefinitionParserDelegate parent = this.delegate;
		this.delegate = createDelegate(getReaderContext(), root, parent);
		// 省略代码....

		preProcessXml(root);
		//只关注此代码
		parseBeanDefinitions(root, this.delegate);
		postProcessXml(root);

		this.delegate = parent;
	}
//接上  只关注Spring自带的解析
	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)) {
						// Spring自带的标签解析
						parseDefaultElement(ele, delegate);
					}
					else {
						delegate.parseCustomElement(ele);
					}
				}
			}
		}
		else {
			delegate.parseCustomElement(root);
		}
	}
	//接上  支持解析Import标签、alias 、bean、beans嵌套的
	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)) {
			//示例中应关注此处解析bean标签
			processBeanDefinition(ele, delegate);
		}
		else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
			// recurse
			doRegisterBeanDefinitions(ele);
		}
	}

	//接上 处理BeanDefinition
	protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
		// 核心解析步骤(使用委托模式)
		BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
		if (bdHolder != null) {
			bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
			try {
				// 注册最终的装饰实例
				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));
		}
	}

	public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) {
		return parseBeanDefinitionElement(ele, null);
	}
	// 解析xml，生成AbstractBeanDefinition对象实例，交给AbstractBeanDefinition管理
	public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
		String id = ele.getAttribute(ID_ATTRIBUTE);
		String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);

		List<String> aliases = new ArrayList<String>();
		//如果使用了name标签，将name作为别名
		if (StringUtils.hasLength(nameAttr)) {
			String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
			aliases.addAll(Arrays.asList(nameArr));
		}

		String beanName = id;
		if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
			beanName = aliases.remove(0);
			if (logger.isDebugEnabled()) {
				logger.debug("No XML 'id' specified - using '" + beanName +
						"' as bean name and " + aliases + " as aliases");
			}
		}

		if (containingBean == null) {
			checkNameUniqueness(beanName, aliases, ele);
		}
		// 解析元素内容成BeanDefinition
		AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
		if (beanDefinition != null) {
			if (!StringUtils.hasText(beanName)) {
				try {
					if (containingBean != null) {
						beanName = BeanDefinitionReaderUtils.generateBeanName(
								beanDefinition, this.readerContext.getRegistry(), true);
					}
					else {
						beanName = this.readerContext.generateBeanName(beanDefinition);
						// Register an alias for the plain bean class name, if still possible,
						// if the generator returned the class name plus a suffix.
						// This is expected for Spring 1.2/2.0 backwards compatibility.
						String beanClassName = beanDefinition.getBeanClassName();
						if (beanClassName != null &&
								beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
								!this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
							aliases.add(beanClassName);
						}
					}
					if (logger.isDebugEnabled()) {
						logger.debug("Neither XML 'id' nor 'name' specified - " +
								"using generated bean name [" + beanName + "]");
					}
				}
				catch (Exception ex) {
					error(ex.getMessage(), ele);
					return null;
				}
			}
			String[] aliasesArray = StringUtils.toStringArray(aliases);
			//包装成BeanDefinitionHolder对象
			return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
		}

		return null;
	}

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

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

		String className = null;
		if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
			className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
		}

		try {
			String parent = null;
			if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
				parent = ele.getAttribute(PARENT_ATTRIBUTE);
			}
			//创建基本的BeanDefinition对象，设置beanName，ParentName，ClassLoader等信息
			AbstractBeanDefinition bd = createBeanDefinition(className, parent);
			//解析比如singleton、lazy-init、scope、abstract等等属性标签，并设置到BeanDefinition(以下简称为bd)实例中
			parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
			// 解析description标签 设置到Bd对象中
			bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
			// 解析meta标签 设置到bd对象中
			parseMetaElements(ele, bd);
			
			// 解析lookup-method标签 设置到bd对象中
			parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
			// 解析replaced-method标签 设置到bd对象中
			parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
			// 解析constructor-arg标签 设置到bd对象中
			parseConstructorArgElements(ele, bd);
			// 解析property标签 设置到bd对象中(比如我们使用datasource时注入的url、user、pwd这些property)
			parsePropertyElements(ele, bd);
			// 解析qualifier标签 设置到bd对象中
			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;
	}

	protected AbstractBeanDefinition createBeanDefinition(String className, String parentName)
			throws ClassNotFoundException {

		return BeanDefinitionReaderUtils.createBeanDefinition(
				parentName, className, this.readerContext.getBeanClassLoader());
	}
org.springframework.beans.factory.support.BeanDefinitionReaderUtils#createBeanDefinition

	public static AbstractBeanDefinition createBeanDefinition(
			String parentName, String className, ClassLoader classLoader) throws ClassNotFoundException {

		GenericBeanDefinition bd = new GenericBeanDefinition();
		bd.setParentName(parentName);
		if (className != null) {
			if (classLoader != null) {
				bd.setBeanClass(ClassUtils.forName(className, classLoader));
			}
			else {
				bd.setBeanClassName(className);
			}
		}
		return bd;
	}

	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));
		}
	}

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

		// Register bean definition under primary name.
		String beanName = definitionHolder.getBeanName();
		// 核心关注这块的逻辑
		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);
			}
		}
	}

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");
		// 如果是AbstractBeanDefinition类型实例 进行validate
		if (beanDefinition instanceof AbstractBeanDefinition) {
			try {
				((AbstractBeanDefinition) beanDefinition).validate();
			}
			catch (BeanDefinitionValidationException ex) {
				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Validation of bean definition failed", ex);
			}
		}

		BeanDefinition oldBeanDefinition;

		oldBeanDefinition = this.beanDefinitionMap.get(beanName);
		// 首次进入 old为空
		if (oldBeanDefinition != null) {
			if (!isAllowBeanDefinitionOverriding()) {
				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 (!beanDefinition.equals(oldBeanDefinition)) {
				if (this.logger.isInfoEnabled()) {
					this.logger.info("Overriding bean definition for bean '" + beanName +
							"' with a different definition: replacing [" + oldBeanDefinition +
							"] with [" + beanDefinition + "]");
				}
			}
			else {
				if (this.logger.isDebugEnabled()) {
					this.logger.debug("Overriding bean definition for bean '" + beanName +
							"' with an equivalent definition: replacing [" + oldBeanDefinition +
							"] with [" + beanDefinition + "]");
				}
			}
			this.beanDefinitionMap.put(beanName, beanDefinition);
		}
		else {
		//首次为false
			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<String>(this.beanDefinitionNames.size() + 1);
					updatedDefinitions.addAll(this.beanDefinitionNames);
					updatedDefinitions.add(beanName);
					this.beanDefinitionNames = updatedDefinitions;
					if (this.manualSingletonNames.contains(beanName)) {
						Set<String> updatedSingletons = new LinkedHashSet<String>(this.manualSingletonNames);
						updatedSingletons.remove(beanName);
						this.manualSingletonNames = updatedSingletons;
					}
				}
			}
			else {
				//仍处于启动注册阶段(即没有真正的实例化，只是将bean的属性定义拿到，还不可以直接使用。)
				
				// Still in startup registration phase
				this.beanDefinitionMap.put(beanName, beanDefinition);
				this.beanDefinitionNames.add(beanName);
				this.manualSingletonNames.remove(beanName);
			}
			this.frozenBeanDefinitionNames = null;
		}

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

synchronized (this.startupShutdownMonitor) {
			try {
				
				// 主要是这个代码
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				finishRefresh();
			}

	protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
		//省略代码....

		// 实例化BeanFactory持有的其他正常的非延迟加载的单例集合
		beanFactory.preInstantiateSingletons();
	}

		List<String> beanNames = new ArrayList<String>(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)) {
					final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
					boolean isEagerInit;
					if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
						isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
							@Override
							public Boolean run() {
								return ((SmartFactoryBean<?>) factory).isEagerInit();
							}
						}, getAccessControlContext());
					}
					else {
						isEagerInit = (factory instanceof SmartFactoryBean &&
								((SmartFactoryBean<?>) factory).isEagerInit());
					}
					if (isEagerInit) {
						getBean(beanName);
					}
				}
				else {
					//我们重点关注的是这个地方哈
					getBean(beanName);
				}
			}
		}

	public Object getBean(String name) throws BeansException {
		return doGetBean(name, null, null, false);
	}

		// 首次进来为空  最后会走下边的逻辑
		Object sharedInstance = getSingleton(beanName);
		// 通过this.beanDefinitionMap得到的  具体可自行查看源码。这里不太花篇幅讲述。
		final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
		//...
		if (mbd.isSingleton()) {
					sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
						@Override
						public Object getObject() throws BeansException {
							try {
							 	//最终创建Bean的逻辑
								return createBean(beanName, mbd, args);
							}
							catch (BeansException ex) {
								destroySingleton(beanName);
								throw ex;
							}
						}
					});
					bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
				}
	//....		
	// 注意这里，会把单例cache起来，在后边可以直接使用
	if (newSingleton) {
		addSingleton(beanName, singletonObject);
	}

			try {
					//回到了AbstractBeanFactory#doGetBean的ObjectFactory的getObject方法，执行其中的createBean方法
					singletonObject = singletonFactory.getObject();
					newSingleton = true;
				}

	AbstractAutowireCapableBeanFactory#createBean(java.lang.Class<T>)
	public <T> T createBean(Class<T> beanClass) throws BeansException {
		// Use prototype bean definition, to avoid registering bean as dependent bean.
		RootBeanDefinition bd = new RootBeanDefinition(beanClass);
		bd.setScope(SCOPE_PROTOTYPE);
		bd.allowCaching = ClassUtils.isCacheSafe(beanClass, getBeanClassLoader());
		return (T) createBean(beanClass.getName(), bd, null);
	}

// 接上
protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
		
		RootBeanDefinition mbdToUse = mbd;
		Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
		if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
			mbdToUse = new RootBeanDefinition(mbd);
			mbdToUse.setBeanClass(resolvedClass);
		}
		try {
			mbdToUse.prepareMethodOverrides();
		}
		catch (BeanDefinitionValidationException ex) {
			
		}

		try {
			// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
			Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
			if (bean != null) {
				return bean;
			}
		}
		catch (Throwable ex) {
			
		}
		// 普通Bean的实例创建
		Object beanInstance = doCreateBean(beanName, mbdToUse, args);
		if (logger.isDebugEnabled()) {
			logger.debug("Finished creating instance of bean '" + beanName + "'");
		}
		return beanInstance;
	}

	BeanWrapper instanceWrapper = null;
		if (mbd.isSingleton()) {
			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
		}
		if (instanceWrapper == null) {
			//创建bean实例的Wrapper对象
			instanceWrapper = createBeanInstance(beanName, mbd, args);
		}
		// bean实例在wrapper中已经创建了(不完整)
		final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
		//省略一些代码。。。
		// Initialize the bean instance.
		Object exposedObject = bean;
		try {
			// 注入property到Bean中
			populateBean(beanName, mbd, instanceWrapper);
			if (exposedObject != null) {
				exposedObject = initializeBean(beanName, exposedObject, mbd);
			}
		}
		//省略一些代码。。。
		return exposedObject;

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, 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());
		}

		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;
				}
			}
		}
		// 一般我们不是FactoryMethod和有参构造(也可以有哈)
		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);
		}
		//没有特殊处理就使用无参构造实例
		// No special handling: simply use no-arg constructor.
		return instantiateBean(beanName, mbd);
	}

protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
		try {
			Object beanInstance;
			final BeanFactory parent = this;
			if (System.getSecurityManager() != null) {
				beanInstance = AccessController.doPrivileged(new PrivilegedAction<Object>() {
					@Override
					public Object run() {
						return getInstantiationStrategy().instantiate(mbd, beanName, parent);
					}
				}, getAccessControlContext());
			}
			else {
				// 一般会走这块代码逻辑来生成bean实例
				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);
		}
	}

public Object instantiate(RootBeanDefinition bd, String beanName, BeanFactory owner) {
		// Don't override the class with CGLIB if no overrides.
		if (bd.getMethodOverrides().isEmpty()) {
			Constructor<?> constructorToUse;
			synchronized (bd.constructorArgumentLock) {
				constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod;
				if (constructorToUse == null) {
					final Class<?> clazz = bd.getBeanClass();
					if (clazz.isInterface()) {
						throw new BeanInstantiationException(clazz, "Specified class is an interface");
					}
					try {
						if (System.getSecurityManager() != null) {
							constructorToUse = AccessController.doPrivileged(new PrivilegedExceptionAction<Constructor<?>>() {
								@Override
								public Constructor<?> run() throws Exception {
									return clazz.getDeclaredConstructor((Class[]) null);
								}
							});
						}
						else {
							//获取xml中bean标签定义的Class的Constructor实例
							constructorToUse =	clazz.getDeclaredConstructor((Class[]) null);
						}
						bd.resolvedConstructorOrFactoryMethod = constructorToUse;
					}
					catch (Throwable ex) {
						throw new BeanInstantiationException(clazz, "No default constructor found", ex);
					}
				}
			}
			//实例化“xml中bean标签定义的Class”
			return BeanUtils.instantiateClass(constructorToUse);
		}
		else {
			// Must generate CGLIB subclass.
			return instantiateWithMethodInjection(bd, beanName, owner);
		}
	}

final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
Object exposedObject = bean;
		try {
			//装载比如Property属性  可以是其他Bean对象，也可能是String等基本属性。  具体见populateBean中的applyPropertyValues方法
			populateBean(beanName, mbd, instanceWrapper);
			if (exposedObject != null) {
				//初始化Bean对象
				exposedObject = initializeBean(beanName, exposedObject, mbd);
			}
		}

protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
		if (System.getSecurityManager() != null) {
			AccessController.doPrivileged(new PrivilegedAction<Object>() {
				@Override
				public Object run() {
					invokeAwareMethods(beanName, bean);
					return null;
				}
			}, getAccessControlContext());
		}
		else {
			//执行wire的method(BeanNameAware、BeanClassLoaderAware、BeanFactoryAware)
			invokeAwareMethods(beanName, bean);
		}

		Object wrappedBean = bean;
		if (mbd == null || !mbd.isSynthetic()) {
			wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
		}

		try {
			//执行init方法
			invokeInitMethods(beanName, wrappedBean, mbd);
		}
		catch (Throwable ex) {
			throw new BeanCreationException(
					(mbd != null ? mbd.getResourceDescription() : null),
					beanName, "Invocation of init method failed", ex);
		}
		if (mbd == null || !mbd.isSynthetic()) {
			wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
		}
		return wrappedBean;
	}

protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd)
			throws Throwable {

		boolean isInitializingBean = (bean instanceof InitializingBean);
		if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
			if (logger.isDebugEnabled()) {
				logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
			}
			if (System.getSecurityManager() != null) {
				try {
					AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
						@Override
						public Object run() throws Exception {
							((InitializingBean) bean).afterPropertiesSet();
							return null;
						}
					}, getAccessControlContext());
				}
				catch (PrivilegedActionException pae) {
					throw pae.getException();
				}
			}
			else {
				((InitializingBean) bean).afterPropertiesSet();
			}
		}

		if (mbd != null) {
			String initMethodName = mbd.getInitMethodName();
			if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
					!mbd.isExternallyManagedInitMethod(initMethodName)) {
				invokeCustomInitMethod(beanName, bean, mbd);
			}
		}
	}

				// Instantiate all remaining (non-lazy-init) singletons.
				finishBeanFactoryInitialization(beanFactory);

 		//ApplicationContext context = new ClassPathXmlApplicationContext("classpath:/spring/test.xml");
        context.getBean(StringUtils.class);

	public <T> T getBean(Class<T> requiredType) throws BeansException {
		assertBeanFactoryActive();
		return getBeanFactory().getBean(requiredType);
	}

	public <T> T getBean(Class<T> requiredType) throws BeansException {
		return getBean(requiredType, (Object[]) null);
	}
	
	@Override
	public <T> T getBean(Class<T> requiredType, Object... args) throws BeansException {
		//获取NamedBeanHolder对象  核心获取SpringBean的逻辑
		NamedBeanHolder<T> namedBean = resolveNamedBean(requiredType, args);
		if (namedBean != null) {
			//最后是这里返回实例
			return namedBean.getBeanInstance();
		}
		BeanFactory parent = getParentBeanFactory();
		if (parent != null) {
			return parent.getBean(requiredType, args);
		}
		throw new NoSuchBeanDefinitionException(requiredType);
	}
	//接上

//requiredType= StringUtil  args=null
private <T> NamedBeanHolder<T> resolveNamedBean(Class<T> requiredType, Object... args) throws BeansException {
		Assert.notNull(requiredType, "Required type must not be null");
		// 根据Class类型获取名字  示例中只有一个["stringutil"]
		String[] candidateNames = getBeanNamesForType(requiredType);

		if (candidateNames.length > 1) {
			List<String> autowireCandidates = new ArrayList<String>(candidateNames.length);
			for (String beanName : candidateNames) {
				if (!containsBeanDefinition(beanName) || getBeanDefinition(beanName).isAutowireCandidate()) {
					autowireCandidates.add(beanName);
				}
			}
			if (!autowireCandidates.isEmpty()) {
				candidateNames = StringUtils.toStringArray(autowireCandidates);
			}
		}
		// 我们示例中length==1 ，beanName=stringutil  和我们定义的id保持一致
		if (candidateNames.length == 1) {
			String beanName = candidateNames[0];
			//注意看下getBean方法的执行逻辑
			return new NamedBeanHolder<T>(beanName, getBean(beanName, requiredType, args));
		}
		else if (candidateNames.length > 1) {
			Map<String, Object> candidates = new LinkedHashMap<String, Object>(candidateNames.length);
			for (String beanName : candidateNames) {
				if (containsSingleton(beanName)) {
					candidates.put(beanName, getBean(beanName, requiredType, args));
				}
				else {
					candidates.put(beanName, getType(beanName));
				}
			}
			String candidateName = determinePrimaryCandidate(candidates, requiredType);
			if (candidateName == null) {
				candidateName = determineHighestPriorityCandidate(candidates, requiredType);
			}
			if (candidateName != null) {
				Object beanInstance = candidates.get(candidateName);
				if (beanInstance instanceof Class) {
					beanInstance = getBean(candidateName, requiredType, args);
				}
				return new NamedBeanHolder<T>(candidateName, (T) beanInstance);
			}
			throw new NoUniqueBeanDefinitionException(requiredType, candidates.keySet());
		}

		return null;
	}

	public String[] getBeanNamesForType(Class<?> type) {
		return getBeanNamesForType(type, true, true);
	}
	// type==StringUtil 不为空
	public String[] getBeanNamesForType(Class<?> type, boolean includeNonSingletons, boolean allowEagerInit) {
		if (!isConfigurationFrozen() || type == null || !allowEagerInit) {
			return doGetBeanNamesForType(ResolvableType.forRawClass(type), includeNonSingletons, allowEagerInit);
		}
		//cache为空 size==0
		Map<Class<?>, String[]> cache =
				(includeNonSingletons ? this.allBeanNamesByType : this.singletonBeanNamesByType);
		String[] resolvedBeanNames = cache.get(type);
		if (resolvedBeanNames != null) {
			return resolvedBeanNames;
		}
		// 会执行这里!!!!
		resolvedBeanNames = doGetBeanNamesForType(ResolvableType.forRawClass(type), includeNonSingletons, true);
		if (ClassUtils.isCacheSafe(type, getBeanClassLoader())) {
			cache.put(type, resolvedBeanNames);
		}
		return resolvedBeanNames;
	}
// 从this.beanDefinitionNames中获取beanName
private String[] doGetBeanNamesForType(ResolvableType type, boolean includeNonSingletons, boolean allowEagerInit) {
		List<String> result = new ArrayList<String>();

		// Check all bean definitions.
		for (String beanName : this.beanDefinitionNames) {
			// Only consider bean as eligible if the bean name
			// is not defined as alias for some other bean.
			if (!isAlias(beanName)) {
				try {
					RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
					// Only check bean definition if it is complete.
					if (!mbd.isAbstract() && (allowEagerInit ||
							(mbd.hasBeanClass() || !mbd.isLazyInit() || isAllowEagerClassLoading()) &&
									!requiresEagerInitForType(mbd.getFactoryBeanName()))) {
						// In case of FactoryBean, match object created by FactoryBean.
						boolean isFactoryBean = isFactoryBean(beanName, mbd);
						BeanDefinitionHolder dbd = mbd.getDecoratedDefinition();
						boolean matchFound =
								(allowEagerInit || !isFactoryBean ||
										(dbd != null && !mbd.isLazyInit()) || containsSingleton(beanName)) &&
								(includeNonSingletons ||
										(dbd != null ? mbd.isSingleton() : isSingleton(beanName))) &&
								isTypeMatch(beanName, type);
						if (!matchFound && isFactoryBean) {
							// In case of FactoryBean, try to match FactoryBean instance itself next.
							beanName = FACTORY_BEAN_PREFIX + beanName;
							matchFound = (includeNonSingletons || mbd.isSingleton()) && isTypeMatch(beanName, type);
						}
						if (matchFound) {
							//最后会执行这里
							result.add(beanName);
						}
					}
				}
				catch (CannotLoadBeanClassException ex) {
					
				}
				catch (BeanDefinitionStoreException ex) {
					
				}
			}
		}

		

		return StringUtils.toStringArray(result);
	}

	public <T> T getBean(String name, Class<T> requiredType, Object... args) throws BeansException {
		return doGetBean(name, requiredType, args, false);
	}
	
	protected <T> T doGetBean(
			final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
			throws BeansException {

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

		// 从缓存中获取。
		Object sharedInstance = getSingleton(beanName);
		if (sharedInstance != null && args == null) {
			bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
		}
		//省略bean创建的代码
		return (T) bean;
	}

		if (namedBean != null) {
			return namedBean.getBeanInstance();
		}

StringUtils sutils=context.getBean(StringUtils.class);