自我分析-Spring IOC

       Spring IOC容器實現原理大致是容器(Map)+反射(Java反射和cglib)。Spring提供豐富的ApplicationContext，以FileSystemXmlApplicationContext來分析IOC容器。

    代碼中大量使用設計模式-模板模式，若不清楚請先看看模板模式再來看具體分析。分析框架代碼時要

多使用查看類繼承和調用關係快捷鍵，快捷鍵可以設置，我是設置爲F1和F4。

    注意：

1.本文重在怎麼自我分析框架代碼，所以對其中解析需自己實際跟蹤代碼實踐方可。 

  2.spring源代碼版本 spring-framework-3.2.1.RELEASE

預覽

org.springframework.beans.factory.BeanFactory，IOC容器根接口。

org.springframework.beans.factory.config.BeanDefinition，Bean實例信息描述接口。

org.springframework.core.io.Resource，Spring配置資源文件接口。

org.springframework.core.io.ResourceLoader，加載配置資源文件接口。

org.springframework.beans.factory.support.BeanDefinitionReader，Bean實例信息描述讀取。

org.springframework.beans.factory.xml.support.BeanDefinitionDocumentReader，Bean實例信息描述xml文檔對象讀取(解析)。

org.springframework.beans.factory.xml.BeanDefinitionParserDelegate，實際解析Spring配置資源文件。

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory，自動裝箱實現類。

IOC容器初始化入口

org.springframework.context.support.FileSystemXmlApplicationContext

public FileSystemXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
		throws BeansException {

	super(parent);
	// 設置Spring配置文件
	setConfigLocations(configLocations);
	if (refresh) {
	// IOC容器初始化入口，詳見其父類AbstractApplicationContext
		refresh();
	}
}

刷新IOC容器，完成資源定位、加載、解析、註冊等

org.springframework.context.support.AbstractApplicationContext

public void refresh() throws BeansException, IllegalStateException {
	
	synchronized (this.startupShutdownMonitor) {
		// Prepare this context for refreshing.
		prepareRefresh();

		// 獲取BeanFactory容器，並完成資源定位、加載、解析、註冊
		ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

		// Prepare the bean factory for use in this context.
		prepareBeanFactory(beanFactory);

		try {
			// Allows post-processing of the bean factory in context subclasses.
			postProcessBeanFactory(beanFactory);

			// Invoke factory processors registered as beans in the context.
			invokeBeanFactoryPostProcessors(beanFactory);

			// Register bean processors that intercept bean creation.
			registerBeanPostProcessors(beanFactory);

			// Initialize message source for this context.
			initMessageSource();

			// Initialize event multicaster for this context.
			initApplicationEventMulticaster();

			// Initialize other special beans in specific context subclasses.
			onRefresh();

			// Check for listener beans and register them.
			registerListeners();

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

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

		catch (BeansException ex) {
			// Destroy already created singletons to avoid dangling resources.
			destroyBeans();

			// Reset 'active' flag.
			cancelRefresh(ex);

			// Propagate exception to caller.
			throw ex;
		}
	}
}

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
	// 刷新BeanFactory，完成資源定位、加載、解析、註冊，詳見其子類AbstractRefreshableApplicationContext
	refreshBeanFactory();
	ConfigurableListableBeanFactory beanFactory = getBeanFactory();
	if (logger.isDebugEnabled()) {
		logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
	}
	return beanFactory;
}

org.springframework.context.support.AbstractRefreshableApplicationContext

protected final void refreshBeanFactory() throws BeansException {
	if (hasBeanFactory()) {
		destroyBeans();
		closeBeanFactory();
	}
	try {
		DefaultListableBeanFactory beanFactory = createBeanFactory();
		beanFactory.setSerializationId(getId());
		customizeBeanFactory(beanFactory);
		// 加載BeanDefinitions，詳見其子類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);
	}
}

讀取資源文件，準備加載BeanDefition

Org.springframework.context.support.AbstractXmlApplicationContext

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);
	// 加載BeanDefitions
	loadBeanDefinitions(beanDefinitionReader);
}

protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
	Resource[] configResources = getConfigResources();
	if (configResources != null) {
		reader.loadBeanDefinitions(configResources);
	}
	String[] configLocations = getConfigLocations();
	if (configLocations != null) {
		reader.loadBeanDefinitions(configLocations);
	}
}

org.springframework.beans.factory.support.AbstractBeanDefinitionReader

public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
	Assert.notNull(locations, "Location array must not be null");
	int counter = 0;
	for (String location : locations) {
	// 讀取資源文件，加載BeanDefitions
		counter += loadBeanDefinitions(location);
	}
	return counter;
}

public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
	ResourceLoader resourceLoader = getResourceLoader();
	if (resourceLoader == null) {
		throw new BeanDefinitionStoreException(
				"Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
	}

	if (resourceLoader instanceof ResourcePatternResolver) {
		// Resource pattern matching available.
		try {
			Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
			int loadCount = loadBeanDefinitions(resources);
			if (actualResources != null) {
				for (Resource resource : resources) {
					actualResources.add(resource);
				}
			}
			if (logger.isDebugEnabled()) {
				logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
			}
			return loadCount;
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException(
					"Could not resolve bean definition resource pattern [" + location + "]", ex);
		}
	}
	else {
		// Can only load single resources by absolute URL,資源定位
		Resource resource = resourceLoader.getResource(location);
		// 加載資源文件，加載BeanDefitions，詳見其子類
		int loadCount = loadBeanDefinitions(resource);
		if (actualResources != null) {
			actualResources.add(resource);
		}
		if (logger.isDebugEnabled()) {
			logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
		}
		return loadCount;
	}
}

入口-解析XML，加載BeanDefinition，註冊BeanDefinition

org.springframework.beans.factory.xml.XmlBeanDefinitionReader

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

public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
	Assert.notNull(encodedResource, "EncodedResource must not be null");
	if (logger.isInfoEnabled()) {
		logger.info("Loading XML bean definitions from " + encodedResource.getResource());
	}

	Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
	if (currentResources == null) {
		currentResources = new HashSet<EncodedResource>(4);
		this.resourcesCurrentlyBeingLoaded.set(currentResources);
	}
	if (!currentResources.add(encodedResource)) {
		throw new BeanDefinitionStoreException(
				"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
	}
	try {
		InputStream inputStream = encodedResource.getResource().getInputStream();
		try {
			InputSource inputSource = new InputSource(inputStream);
			if (encodedResource.getEncoding() != null) {
				inputSource.setEncoding(encodedResource.getEncoding());
			}
			// 加載BeanDefition
			return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
		}
		finally {
			inputStream.close();
		}
	}
	catch (IOException ex) {
		throw new BeanDefinitionStoreException(
				"IOException parsing XML document from " + encodedResource.getResource(), ex);
	}
	finally {
		currentResources.remove(encodedResource);
		if (currentResources.isEmpty()) {
			this.resourcesCurrentlyBeingLoaded.remove();
		}
	}
}

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
		throws BeanDefinitionStoreException {
	try {
		int validationMode = getValidationModeForResource(resource);
		// 獲取資源文件的docment
		Document doc = this.documentLoader.loadDocument(
				inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());
		// 解析資源文件並註冊BeanDefinitions
		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);
	}
}

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
	BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
	documentReader.setEnvironment(this.getEnvironment());
	int countBefore = getRegistry().getBeanDefinitionCount();
	// 加載BeanDefitions並註冊，詳見其子類DefaultBeanDefinitionDocumentReader
	documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
	return getRegistry().getBeanDefinitionCount() - countBefore;
}

具體解析XML，加載BeanDefinition

org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader

public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
	this.readerContext = readerContext;

	logger.debug("Loading bean definitions");
	Element root = doc.getDocumentElement();
	// 加載、註冊BeanDefitions
	doRegisterBeanDefinitions(root);
}

protected void doRegisterBeanDefinitions(Element root) {
	String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
	if (StringUtils.hasText(profileSpec)) {
		Assert.state(this.environment != null, "environment property must not be null");
		String[] specifiedProfiles = StringUtils.tokenizeToStringArray(profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
		if (!this.environment.acceptsProfiles(specifiedProfiles)) {
			return;
		}
	}

	// any nested <beans> elements will cause recursion in this method. In
	// order to propagate and preserve <beans> default-* attributes correctly,
	// keep track of the current (parent) delegate, which may be null. Create
	// the new (child) delegate with a reference to the parent for fallback purposes,
	// then ultimately reset this.delegate back to its original (parent) reference.
	// this behavior emulates a stack of delegates without actually necessitating one.
	BeanDefinitionParserDelegate parent = this.delegate;
	this.delegate = createHelper(readerContext, root, parent);

	preProcessXml(root);
	// 解析BeanDefinitions
	parseBeanDefinitions(root, this.delegate);
	postProcessXml(root);

	this.delegate = parent;
}

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

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
	if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
		importBeanDefinitionResource(ele);
	}
	else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
		processAliasRegistration(ele);
	}
	else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
	// 解析bean
		processBeanDefinition(ele, delegate);
	}
	else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
		// recurse
		doRegisterBeanDefinitions(ele);
	}
}

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));
	}
}

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
	// 解析BEAN，將解析的BeanDefinition包裝下，實質解析交給委派類
	BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
	if (bdHolder != null) {
		bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
		try {
			// 註冊BeanDefinition，即註冊到BeanFactory中
			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));
	}
}

實質解析XML

org.springframework.beans.factory.xml.BeanDefinitionParserDelegate

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>();
	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);
		return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
	}

	return null;
}

// 具體解析就在BeanDefinitionParserDelegate類，若想知道具體怎麼解析的，請查看此類即可
public Object parsePropertySubElement(Element ele, BeanDefinition bd, String defaultValueType) {
	if (!isDefaultNamespace(ele)) {
		return parseNestedCustomElement(ele, bd);
	}
	else if (nodeNameEquals(ele, BEAN_ELEMENT)) {
		BeanDefinitionHolder nestedBd = parseBeanDefinitionElement(ele, bd);
		if (nestedBd != null) {
			nestedBd = decorateBeanDefinitionIfRequired(ele, nestedBd, bd);
		}
		return nestedBd;
	}
	else if (nodeNameEquals(ele, REF_ELEMENT)) {
		// A generic reference to any name of any bean.
		String refName = ele.getAttribute(BEAN_REF_ATTRIBUTE);
		boolean toParent = false;
		if (!StringUtils.hasLength(refName)) {
			// A reference to the id of another bean in the same XML file.
			refName = ele.getAttribute(LOCAL_REF_ATTRIBUTE);
			if (!StringUtils.hasLength(refName)) {
				// A reference to the id of another bean in a parent context.
				refName = ele.getAttribute(PARENT_REF_ATTRIBUTE);
				toParent = true;
				if (!StringUtils.hasLength(refName)) {
					error("'bean', 'local' or 'parent' is required for <ref> element", ele);
					return null;
				}
			}
		}
		if (!StringUtils.hasText(refName)) {
			error("<ref> element contains empty target attribute", ele);
			return null;
		}
		RuntimeBeanReference ref = new RuntimeBeanReference(refName, toParent);
		ref.setSource(extractSource(ele));
		return ref;
	}
	else if (nodeNameEquals(ele, IDREF_ELEMENT)) {
		return parseIdRefElement(ele);
	}
	else if (nodeNameEquals(ele, VALUE_ELEMENT)) {
		return parseValueElement(ele, defaultValueType);
	}
	else if (nodeNameEquals(ele, NULL_ELEMENT)) {
		// It's a distinguished null value. Let's wrap it in a TypedStringValue
		// object in order to preserve the source location.
		TypedStringValue nullHolder = new TypedStringValue(null);
		nullHolder.setSource(extractSource(ele));
		return nullHolder;
	}
	else if (nodeNameEquals(ele, ARRAY_ELEMENT)) {
		return parseArrayElement(ele, bd);
	}
	else if (nodeNameEquals(ele, LIST_ELEMENT)) {
		return parseListElement(ele, bd);
	}
	else if (nodeNameEquals(ele, SET_ELEMENT)) {
		return parseSetElement(ele, bd);
	}
	else if (nodeNameEquals(ele, MAP_ELEMENT)) {
		return parseMapElement(ele, bd);
	}
	else if (nodeNameEquals(ele, PROPS_ELEMENT)) {
		return parsePropsElement(ele);
	}
	else {
		error("Unknown property sub-element: [" + ele.getNodeName() + "]", ele);
		return null;
	}
}

註冊BeanDefinition

BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
從上面代碼分析中可知道，將BeanDefinition註冊到BeanFacotry

org.springframework.beans.factory.support.BeanDefinitionReaderUtils

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

	// Register bean definition under primary name.
	String beanName = definitionHolder.getBeanName();
	// 具體註冊，詳見其子類DefaultListableBeanFactory
	registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

	// Register aliases for bean name, if any.
	String[] aliases = definitionHolder.getAliases();
	if (aliases != null) {
		for (String aliase : aliases) {
			registry.registerAlias(beanName, aliase);
		}
	}
}

org.springframework.beans.factory.support.DefaultListableBeanFactory

public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
		throws BeanDefinitionStoreException {

	Assert.hasText(beanName, "Bean name must not be empty");
	Assert.notNull(beanDefinition, "BeanDefinition must not be null");

	if (beanDefinition instanceof AbstractBeanDefinition) {
		try {
			((AbstractBeanDefinition) beanDefinition).validate();
		}
		catch (BeanDefinitionValidationException ex) {
			throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
					"Validation of bean definition failed", ex);
		}
	}

	synchronized (this.beanDefinitionMap) {
		Object oldBeanDefinition = this.beanDefinitionMap.get(beanName);
		if (oldBeanDefinition != null) {
			if (!this.allowBeanDefinitionOverriding) {
				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
						"': There is already [" + oldBeanDefinition + "] bound.");
			}
			else {
				if (this.logger.isInfoEnabled()) {
					this.logger.info("Overriding bean definition for bean '" + beanName +
							"': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
				}
			}
		}
		else {
			this.beanDefinitionNames.add(beanName);
			this.frozenBeanDefinitionNames = null;
		}
		this.beanDefinitionMap.put(beanName, beanDefinition);
	}

	resetBeanDefinition(beanName);
}

// 這就是BeanDefinition存放的容器
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(64);

至此我們瞭解了IOC的資源定位、加載、解析、註冊，但還未初始化對象和設置屬性和依賴關係，

而此行爲發生在getBean()中

GetBean初始化對象

org.springframework.context.support.AbstractApplicationContext

public Object getBean(String name) throws BeansException {
	return getBeanFactory().getBean(name);
}

上面代碼分析中可以知道getBeanFactory()其子類AbstractRefreshableApplicationContext中實現，getBeanFactory()

返回DefaultListableBeanFactory，而getBean(String)在DefaultListableBeanFactory父類AbstractBeanFactory中

org.springframework.beans.factory.support.AbstractBeanFactory

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

	// 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 (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);
		}

		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 dependsOnBean : dependsOn) {
				getBean(dependsOnBean);  // 這裏是對依賴對象進行創建
				registerDependentBean(dependsOnBean, beanName);
			}
		}

		// Create bean instance.
		if (mbd.isSingleton()) {
			sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
				public Object getObject() throws BeansException {
					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);  //創建bean，這裏就是實質的注入屬性等
			}
			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 '" + scopeName + "'");
			}
			try {
				Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
					public Object getObject() throws BeansException {
						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);
			}
		}
	}

	// Check if required type matches the type of the actual bean instance.
	if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
		try {
			return getTypeConverter().convertIfNecessary(bean, requiredType);
		}
		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;
}

從doGetBean方法中我們得到很多信息(具體自己跟蹤下看看)，其中調用了關鍵方法createBean
詳見其子類AbstractAutowireCapableBeanFactory(看類名就知道了)。

初始化對象，設置屬性和依賴關係

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory
protected Object createBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
		throws BeanCreationException {

	if (logger.isDebugEnabled()) {
		logger.debug("Creating instance of bean '" + beanName + "'");
	}
	// Make sure bean class is actually resolved at this point.
	resolveBeanClass(mbd, beanName);

	// Prepare method overrides.
	try {
		mbd.prepareMethodOverrides();
	}
	catch (BeanDefinitionValidationException ex) {
		throw new BeanDefinitionStoreException(mbd.getResourceDescription(),
				beanName, "Validation of method overrides failed", ex);
	}

	try {
		// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
		Object bean = resolveBeforeInstantiation(beanName, mbd);
		if (bean != null) {
			return bean;
		}
	}
	catch (Throwable ex) {
		throw new BeanCreationException(mbd.getResourceDescription(), beanName,
				"BeanPostProcessor before instantiation of bean failed", ex);
	}

	Object beanInstance = doCreateBean(beanName, mbd, args);
	if (logger.isDebugEnabled()) {
		logger.debug("Finished creating instance of bean '" + beanName + "'");
	}
	return beanInstance;
}

從上面一步步分析到這裏，對IOC容器的實現思路已較清楚，接下來自動裝箱的實現自己跟組代碼分析吧。

整個代碼分析後，本人感觸很深，spring框架代碼確實是高內聚低耦合，整個分析過後，再回想IOC的實現，
其實沒有想象中那麼難，本文分析中很多具體的實現還需讀者自己去跟蹤代碼去看看怎麼實現的。望讀者能一邊
跟蹤代碼一邊看本文，若不自己實踐操作，僅一眼過去效果不會很大。

若文中存在分析錯誤，望留言指出，在此非常感謝。