Spring源码情操陶冶-AbstractApplicationContext#obtainFreshBeanFactory

前言-阅读源码有利于陶冶情操，本文承接前文Spring源码情操陶冶-AbstractApplicationContext
约束：

1. 本文指定contextClass为默认的XmlWebApplicationContext
2. 从属AbstractApplicationContext#refresh方法

AbstractApplicationContext#obtainFreshBeanFactory

该方法主要完成创建Bean工厂，涉及到解析spring文件，代码清单如下

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
		//更新bean工厂，其会销毁已存在的bean内容并重新创建
		refreshBeanFactory();
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		if (logger.isDebugEnabled()) {
			logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
		}
		return beanFactory;
	}

由以上代码所见，关键方法指向子类AbstractRefreshableApplicationContext#refreshBeanFactory,代码清单如下

protected final void refreshBeanFactory() throws BeansException {
		//存在已有bean工厂则销毁
		if (hasBeanFactory()) {
			destroyBeans();
			closeBeanFactory();
		}
		try {
			//创建默认的用List接口存放bean的工厂
			DefaultListableBeanFactory beanFactory = createBeanFactory();
			//这里同contextId
			beanFactory.setSerializationId(getId());
			//配置allowBeanDefinitionOverriding和allowCircularReferences属性，这里均不设置
			customizeBeanFactory(beanFactory);
			//调用子类的加载bean定义方法，这里会调用XmlWebApplicationContext子类的复写方法
			loadBeanDefinitions(beanFactory);
			synchronized (this.beanFactoryMonitor) {
				this.beanFactory = beanFactory;
			}
		}
		catch (IOException ex) {
			throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
		}
	}

XmlWebApplicationContext#loadBeanDefinitions

加载bean预方法，代码清单如下

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.
		//环境为StardEvironment对象
		beanDefinitionReader.setEnvironment(getEnvironment());
		//资源加载器为XmlWebApplicationContext
		beanDefinitionReader.setResourceLoader(this);
		//实体分解器为ResourceEntityResolver对象，主要用于javax.xml.parse解析xml所用
		beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

		// Allow a subclass to provide custom initialization of the reader,
		// then proceed with actually loading the bean definitions.
		//此处为空方法
		initBeanDefinitionReader(beanDefinitionReader);
		//真切的开始加载bean
		loadBeanDefinitions(beanDefinitionReader);
	}

紧接着查看真实的加载bean方法XmlWebApplicationContext#loadBeanDefinitions(XmlBeanDefinitionReader reader)，代码清单如下

protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {
		//获取spring配置文件的位置列表
		String[] configLocations = getConfigLocations();
		if (configLocations != null) {
			for (String configLocation : configLocations) {
				//读取加载
				reader.loadBeanDefinitions(configLocation);
			}
		}
	}

AbstractBeanDefinitionReader#loadBeanDefinitions

真实的加载bean内容可追溯到XmlBeanDefinitionReader的父类AbstractBeanDefinitionReader#loadBeanDefinitions(String location, Set<Resource> actualResources)方法，代码清单如下

//此处的actualResources参数传过来为null
public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
		//此处的ResourceLoader为XmlWebApplicationContext
		ResourceLoader resourceLoader = getResourceLoader();
		if (resourceLoader == null) {
			throw new BeanDefinitionStoreException(
					"Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
		}
		//XmlWebApplicationContext符合此条件
		if (resourceLoader instanceof ResourcePatternResolver) {
			// Resource pattern matching available.
			try {
				//调用的是AbstractApplicationContext的getResources方法，追溯一下调用的其实是PathMatchingResourcePatternResolver.getResources方法，其会搜寻指定目录符合条件的文件集合
				Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
				//加载某个spring bean文件
				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;
		}
	}

略过一些代码调用，直接看XmlBeanDefinitionReader#registerBeanDefinitions(Document doc,Resource resource)注册bean定义方法，代码清单如下

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
		documentReader.setEnvironment(this.getEnvironment());
		//此处的getRegistry()方法返回的实例为DefaultListableBeanFactory类型
		int countBefore = getRegistry().getBeanDefinitionCount();
		//调用DefaultBeanDefinitionDocumentReader.registerBeanDefinitions方法
		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
		return getRegistry().getBeanDefinitionCount() - countBefore;
	}

DefaultBeanDefinitionDocumentReader#registerBeanDefinitions

代码清单如下

	//解析bean定义
	public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
		this.readerContext = readerContext;
		logger.debug("Loading bean definitions");
		//此处的root节点一般为<beans>节点
		Element root = doc.getDocumentElement();
		//具体解析的方法
		doRegisterBeanDefinitions(root);
	}

解析bean具体方法DefaultBeanDefinitionDocumentReader#doRegisterBeanDefinitions，代码清单如下

protected void doRegisterBeanDefinitions(Element root) {
		//此处针对<beans>的节点属性profile进行的操作
		String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
		if (StringUtils.hasText(profileSpec)) {
			Assert.state(this.environment != null, "Environment must be set for evaluating profiles");
			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;
                //读取<beans>标签中的default-*属性
		this.delegate = createDelegate(this.readerContext, root, parent);
		//预处理bean xml配置文件中的自定义标签，默认是为空的
		preProcessXml(root);
		//解析bean xml配置文件
		parseBeanDefinitions(root, this.delegate);
		//处理bean xml配置文件中的自定义标签，默认是为空的
		postProcessXml(root);

		this.delegate = parent;
	}

从上述的注释可知，我们只需关注DefaultBeanDefinitionDocumentReader#parseBeanDefinitions对bean xml文件的解析，鉴于其重要性，将于下一章节详细解读

下节预告

Spring源码情操陶冶-DefaultBeanDefinitionDocumentReader#parseBeanDefinitions