Spring源码分析之BeanFactory初始化

在上一篇Spring源码分析之IOC容器创建过程中，大致梳理了一下IOC容器初始化的流程。在初始化的过程中，会调用模板方法refresh(),在刷新工厂方法中，首先会获取beanFactory，即以下这行代码：

ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

beanFactory的初始化大致可分为：定位---解析---注册   这三个步骤。以下将从源码的角度分析bean工厂是如何初始化的。入口为：AbstractApplicationContext的obtainFreshBeanFactory方法：

	protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        //具体的子类来实现
		refreshBeanFactory();
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		if (logger.isDebugEnabled()) {
			logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
		}
		return beanFactory;
	}

     
    	protected final void refreshBeanFactory() throws BeansException {
		//判断bean工厂是否存在，存在先关闭销毁
		if (hasBeanFactory()) {
			destroyBeans();
			closeBeanFactory();
		}
		try {
			//这里只是简单的创建了DefaultListableBeanFactory 的实例
			DefaultListableBeanFactory beanFactory = createBeanFactory();
			beanFactory.setSerializationId(getId());
			//工厂的定制化设置
			customizeBeanFactory(beanFactory);
			//实际加载解析bean定义的入口
			loadBeanDefinitions(beanFactory);
			synchronized (this.beanFactoryMonitor) {
				this.beanFactory = beanFactory;
			}
		}
		catch (IOException ex) {
			throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
		}
	}

（2）AbstractXmlApplicationContext的loadBeanDefinitions方法

	protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
		//创建一个bean定义读取器beanDefinitionReader 
		XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
		beanDefinitionReader.setEnvironment(this.getEnvironment());
		//设置资源加载器
		beanDefinitionReader.setResourceLoader(this);
		//为Bean读取器设置SAX xml解析器
		beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
		//xml校验相关
		initBeanDefinitionReader(beanDefinitionReader);
		//加载bean的地方
		loadBeanDefinitions(beanDefinitionReader);
	}

	protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
		//循环的去加载配置文件
		Resource[] configResources = getConfigResources();
		if (configResources != null) {
			reader.loadBeanDefinitions(configResources);
		}
		String[] configLocations = getConfigLocations();
		if (configLocations != null) {
			reader.loadBeanDefinitions(configLocations);
		}
	}

（3）AbstractBeanDefinitionReader的loadBeanDefinitions方法,通过资源路径  解析为Spring标准的resource资源

	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;
	}
	public int loadBeanDefinitions(String location, Set actualResources) throws BeanDefinitionStoreException {
		//获取初始化过程中的资源加载器
		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
				Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
				//委派实现加载
				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;
		}
	}

（4）XmlBeanDefinitionReader 的loadBeanDefinitions方法

	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 currentResources = this.resourcesCurrentlyBeingLoaded.get();
		if (currentResources == null) {
			currentResources = new HashSet(4);
			this.resourcesCurrentlyBeingLoaded.set(currentResources);
		}
		if (!currentResources.add(encodedResource)) {
			throw new BeanDefinitionStoreException(
					"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
		}
		try {
			//将配置资源解析为流的形式
			InputStream inputStream = encodedResource.getResource().getInputStream();
			try {
				InputSource inputSource = new InputSource(inputStream);
				if (encodedResource.getEncoding() != null) {
					inputSource.setEncoding(encodedResource.getEncoding());
				}
				//开始正式的加载配置文件
				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 {
			//转换为Document对象，方便后面对各个元素来进行解析
			Document doc = doLoadDocument(inputSource, resource);
			//解析Document对象
			return registerBeanDefinitions(doc, resource);
		}
		catch (BeanDefinitionStoreException ex) {
			throw 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 {
		//创建Document解析器
		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
		//获取已经注册到IOC容器中bean的数量
		int countBefore = getRegistry().getBeanDefinitionCount();
		//注册解析
		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
		return getRegistry().getBeanDefinitionCount() - countBefore;
	}

（4）DefaultBeanDefinitionDocumentReader的registerBeanDefinitions方法，此步骤完成了bean的解析以及注册

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

	protected void doRegisterBeanDefinitions(Element root) {
		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)) {
					return;
				}
			}
		}
		//解析bean定义之前的自定义操作，可用于子类实现相关的接口来定制化操作
		preProcessXml(root);
		//从根元素开始解析
		parseBeanDefinitions(root, this.delegate);
		//解析bean定义之前的自定义操作，方便扩展
		postProcessXml(root);

		this.delegate = parent;
	}

	protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
		//是否是Spring的默认空间
		if (delegate.isDefaultNamespace(root)) {
			//获取根元素下的所有子节点
			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)) {
						//是Spring自定义的则使用默认的方法是解析
						parseDefaultElement(ele, delegate);
					}
					else {
						//使用用户自定义的方式去解析
						delegate.parseCustomElement(ele);
					}
				}
			}
		}
		else {
			//使用用户自定义的规则去解析元素
			delegate.parseCustomElement(root);
		}
	}

	private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
		//包含import节点的  则解析
		if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
			importBeanDefinitionResource(ele);
		}
		//包含alias节点的  则开始解析
		else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
			processAliasRegistration(ele);
		}
		//包含bean节点的  则开始解析 bean是我们经常会用到的 讲深入分析这个入口
		else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
			processBeanDefinition(ele, delegate);
		}
		//包含beans节点的
		else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
			// recurse
			doRegisterBeanDefinitions(ele);
		}
	}

	protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
		//解析文档Element 成Spring标准描述bean文件beanDefinition（bean解析）
		BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
		if (bdHolder != null) {
			bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
			try {
				// bean定义的注册  即存放到一个map中 key为bean的名字  value为beanDefinition（注册）
				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));
		}
	}

至此，beanFactory就完成了整个的定位-解析--注册的流程。bean的定义信息就保存在beanDefinitionMap中，之后的实例化，依赖注入都是根据beanDefinitionMap中的定义信息来的。初始化之后的beanFactory的结构可以参考如下：

除了Spring默认的初始化的一些bean的定义信息外，还有我们自定义的两个bean，demoA 和 demoB，定义信息中包含每个bean的详细的信息，包含是否是单例，类路径等等。