spring源码-2.1.解析xml准备

这一节我们来看一下obtainFreshBeanFactory都做了什么，这个方法主要就是创建了BeanFactory：

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
    //创建BeanFactory
	refreshBeanFactory();
	//返回BeanFactory
	return getBeanFactory();
}

进入refreshBeanFactory（AbstractRefreshableApplicationContext.refreshBeanFactory()）：

protected final void refreshBeanFactory() throws BeansException {
    //如果已经有beanFactory，那么先清除
	if (hasBeanFactory()) {
		destroyBeans();
		closeBeanFactory();
	}
	try {
	    //创建beanFactory，这里就是new了一个DefaultListableBeanFactory
		DefaultListableBeanFactory beanFactory = createBeanFactory();
		//给beanFactory设置SerializationId
		beanFactory.setSerializationId(getId());
		/**
		* 这个方法中做了两件事：
		* 1.如果ApplicationContext中的allowBeanDefinitionOverriding值(允许beanDefinition覆盖)不为null，则赋值给beanFactory
		* 2.如果ApplicationContext中的allowCircularReferences值(允许循环依赖)不为null，则赋值给beanFactory
		* 注意：这两个值在创建beanFactory的时候，默认都是true
		*/
		customizeBeanFactory(beanFactory);
		//解析xml，load文件中bean的定义
		loadBeanDefinitions(beanFactory);
		synchronized (this.beanFactoryMonitor) {
		    //将初始化好的beanFactory赋值给applicationContext中的beanFactory
			this.beanFactory = beanFactory;
		}
	}
	catch (IOException ex) {
		throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
	}
}

不难看出，核心代码为loadBeanDefinitions(beanFactory)：

protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
	//通过beanFactory创建一个XmlBeanDefinitionReader
	//主要是将XmlBeanDefinitionReader的BeanDefinitionRegistry设置成beanFactory
	XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

	//给reader对象设置environment
	beanDefinitionReader.setEnvironment(this.getEnvironment());
	//将自身（AbstractXmlApplicationContext）作为ResourceLoader，解析xml时要用到
	beanDefinitionReader.setResourceLoader(this);
	//设置EntityResolver
	beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

	//设置两个参数,validationMode和namespaceAware
	initBeanDefinitionReader(beanDefinitionReader);
	//准备读取解析xml
	loadBeanDefinitions(beanDefinitionReader);
}

进入loadBeanDefinitions(beanDefinitionReader):

protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
    //获取配置文件的path，如果之前没有设置，那么为null
	Resource[] configResources = getConfigResources();
	if (configResources != null) {
		reader.loadBeanDefinitions(configResources);
	}
	//在refresh之前设置的配置文件的path
	String[] configLocations = getConfigLocations();
	if (configLocations != null) {
	    //准备解析读取xml
		reader.loadBeanDefinitions(configLocations);
	}
}

继续进入reader.loadBeanDefinitions(configLocations):

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

这里就是做了一个校验，并做了计数，继续进入loadBeanDefinitions(location):

//这里的参数actualResources为null
public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
    //获取resourceLoader对象，就是之前set的applicationContext对象
	ResourceLoader resourceLoader = getResourceLoader();
	if (resourceLoader == null) {
		throw new BeanDefinitionStoreException(
				"Cannot load bean definitions from location [" + location + "]: no ResourceLoader available");
	}
	if (resourceLoader instanceof ResourcePatternResolver) {
		try {
		    //将配置文件抽象成resource对象
			Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
			//解析resource对象
			int count = loadBeanDefinitions(resources);
			if (actualResources != null) {
				Collections.addAll(actualResources, resources);
			}
			if (logger.isTraceEnabled()) {
				logger.trace("Loaded " + count + " bean definitions from location pattern [" + location + "]");
			}
			return count;
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException(
					"Could not resolve bean definition resource pattern [" + location + "]", ex);
		}
	}
	else {
		……和if中的逻辑一样
	}
}

进入到loadBeanDefinitions(resources):

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

继续进入loadBeanDefinitions(resource):

//在进入之前会先将resource对象封装成EncodedResource
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
    //去看看有没有正在被本线程load的resource，如果没有，则将参数中的resource添加进去
	Set<EncodedResource> 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xml文件抽象成的resource对象转换成输入流
		InputStream inputStream = encodedResource.getResource().getInputStream();
		try {
			InputSource inputSource = new InputSource(inputStream);
			if (encodedResource.getEncoding() != null) {
				inputSource.setEncoding(encodedResource.getEncoding());
			}
			//解析xml,加载beanDefinitions
			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();
		}
	}
}

继续进入doLoadBeanDefinitions(inputSource, encodedResource.getResource())：

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
			throws BeanDefinitionStoreException {

	try {
	    //将resource再抽象成document对象
		Document doc = doLoadDocument(inputSource, resource);
		//解析document对象为beanDefinition，并register
		int count = registerBeanDefinitions(doc, resource);
		if (logger.isDebugEnabled()) {
			logger.debug("Loaded " + count + " bean definitions from " + resource);
		}
		return count;
	}
	catch ……
}

继续进入registerBeanDefinitions(doc, resource)：

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
    //初始化一个DocumentReader对象
	BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
	int countBefore = getRegistry().getBeanDefinitionCount();
	//将解析出来的beanDefinitions注册到这个documentReader对象上
	documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
	return getRegistry().getBeanDefinitionCount() - countBefore;
}

继续进入documentReader.registerBeanDefinitions(doc, createReaderContext(resource)):

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public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
    //设置一下在上一步中初始化出来的readerContext
	this.readerContext = readerContext;
	//注册beanDefinitions
	doRegisterBeanDefinitions(doc.getDocumentElement());
}

继续进入doRegisterBeanDefinitions(doc.getDocumentElement()):

protected void doRegisterBeanDefinitions(Element root) {
	BeanDefinitionParserDelegate parent = this.delegate;
	//创建delegate对象，如果root标签中设置了默认的属性，也会一并设置到default属性中
	this.delegate = createDelegate(getReaderContext(), root, parent);
    //如果是root级标签，则校验其profile属性，如果在对应的环境不需要加载，那么直接跳过
    //例如设置profile="!dev",那么在dev环境中不加载该配置
	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.isDebugEnabled()) {
					logger.debug("Skipped XML bean definition file due to specified profiles [" + profileSpec +
							"] not matching: " + getReaderContext().getResource());
				}
				return;
			}
		}
	}
    //空方法，可有用户自定义实现
	preProcessXml(root);
	//解析出beanDefinitions
	parseBeanDefinitions(root, this.delegate);
	//空方法，可有用户自定义实现
	postProcessXml(root);
	this.delegate = parent;
}

继续进入parseBeanDefinitions(root, this.delegate):

protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
    //这里首先判断root元素的nameSpace是不是默认的
    //判断依据为是否为：http://www.springframework.org/schema/beans
	if (delegate.isDefaultNamespace(root)) {
	    /**
	    * 获取所有的子标签，判断是否为默认名称空间
	    * 如果是，则进行默认标签解析
	    * 如果不是，则进行自定义标签解析
	    */
		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)) {
				    //解析默认标签
					parseDefaultElement(ele, delegate);
				}
				else {
				    //解析自定义标签
					delegate.parseCustomElement(ele);
				}
			}
		}
	}
	else {
	    //如果不是默认的，那么进行自定义标签解析
		delegate.parseCustomElement(root);
	}
}

这边会对每一个子标签进行解析，分为默认标签解析（import,bean等标签）和自定义标签的解析，下一节详细看一下默认标签的解析。