[Java知识库]Spring IOC容器刷新BeanFactory（XML配置方式）

Spring IOC容器刷新BeanFactory

前言

? ? Spring IOC容器刷新BeanFactory是一个很复杂的过程，本文将基于XML配置的方式展开分析一下Spring IOC容器刷新BeanFactory的过程，如有误还请指出。

告诉子类刷新内部BeanFactory

    public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
            // 上下文刷新前准备
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
            // 告诉子类刷新内部BeanFactory
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
            // 使用上下文前对bean工厂的一些准备工作
			prepareBeanFactory(beanFactory);

            // ...省略
    }

告诉子类刷新内部BeanFactory

? ? 这里做了两件事：

1. refreshBeanFactory();刷新bean工厂
2. getBeanFactory();获取bean工厂

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
		refreshBeanFactory();
		return getBeanFactory();
	}

刷新bean工厂

刷新bean工厂主要做了以下几件事

1. 如果有bean工厂先销毁和关闭bean工厂
2. 创建bean工厂
3. bean工厂定制
4. 加载bean定义

	@Override
	protected final void refreshBeanFactory() throws BeansException {
        // 1
		if (hasBeanFactory()) {
			destroyBeans();
			closeBeanFactory();
		}
		try {
            // 2
			DefaultListableBeanFactory beanFactory = createBeanFactory();
			beanFactory.setSerializationId(getId());
            // 3
			customizeBeanFactory(beanFactory);
            // 4
			loadBeanDefinitions(beanFactory);
			this.beanFactory = beanFactory;
		}
		catch (IOException ex) {
			throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
		}
	}

展开看一下加载bean定义

• AbstractXmlApplicationContext重写的loadBeanDefinitions方法

    @Override
	protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
		// 为beanFactory创建一个XmlBeanDefinitionReader
		XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

		// 资源加载环境
		beanDefinitionReader.setEnvironment(this.getEnvironment());
		beanDefinitionReader.setResourceLoader(this);
        // bean定义阅读器
		beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

		// 允许子类提供阅读器的自定义初始化
		initBeanDefinitionReader(beanDefinitionReader);
        // 加载bean定义
		loadBeanDefinitions(beanDefinitionReader);
	}

    /**
    这里做了两件事
    1.如果存在根据资源获取bean定义那就根据资源获取
    2.如果存在根据配置路径获取bean定义就根据路径记载bean定义
    */
    protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
        // 根据配置资源加载bean定义
		Resource[] configResources = getConfigResources();
		if (configResources != null) {
			reader.loadBeanDefinitions(configResources);
		}
        // 根据配置路径加载bean定义
		String[] configLocations = getConfigLocations();
		if (configLocations != null) {
			reader.loadBeanDefinitions(configLocations);
		}
	}

• 加载bean定义

    @Override
	public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
		Assert.notNull(locations, "Location array must not be null");
		int count = 0;
        // 加载bean定义
		for (String location : locations) {
			count += loadBeanDefinitions(location);
		}
        // 返回加载bean资源次数
		return count;
	}

    ...省略

    public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
        // 资源加载器
		ResourceLoader resourceLoader = getResourceLoader();
		if (resourceLoader == null) {
			throw new BeanDefinitionStoreException(
					"Cannot load bean definitions from location [" + location + "]: no ResourceLoader available");
		}
        // 资源加载器为资源模式的解析器根据资源加载bean定义
		if (resourceLoader instanceof ResourcePatternResolver) {
			// Resource pattern matching available.
			try {
				Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
				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 {
			// 根据路径获取资源，并加载bean定义
			Resource resource = resourceLoader.getResource(location);
			int count = loadBeanDefinitions(resource);
			if (actualResources != null) {
				actualResources.add(resource);
			}
			if (logger.isTraceEnabled()) {
				logger.trace("Loaded " + count + " bean definitions from location [" + location + "]");
			}
			return count;
		}
	}

这里做了如下的几件事

1. 根据配置资源加载bean定义
2. 根据配置路径加载bean定义

• 这里我们看一下根据路径加载bean定义

通过XmlBeanDedinitionReader``loadBeanDefinitions方法根据配置路径加载bean定义

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

		Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();

		if (!currentResources.add(encodedResource)) {
			throw new BeanDefinitionStoreException(
					"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
		}

		try (InputStream inputStream = encodedResource.getResource().getInputStream()) {
			InputSource inputSource = new InputSource(inputStream);
			if (encodedResource.getEncoding() != null) {
				inputSource.setEncoding(encodedResource.getEncoding());
			}
			return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException(
					"IOException parsing XML document from " + encodedResource.getResource(), ex);
		}
		finally {
			currentResources.remove(encodedResource);
			if (currentResources.isEmpty()) {
				this.resourcesCurrentlyBeingLoaded.remove();
			}
		}
	}

这里主要干了两件事：

1. 从XML加载bean定义，这里加载XML的细节我们先不管了，这并非加载bean定义的核心
2. 加载bean定义doLoadBeanDefinitions，干事儿的都是do开头

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

		try {
            // 加载XML中的bean定义，这里使用的是SAX
			Document doc = doLoadDocument(inputSource, resource);
            // 注册bean定义
			int count = registerBeanDefinitions(doc, resource);
			if (logger.isDebugEnabled()) {
				logger.debug("Loaded " + count + " bean definitions from " + resource);
			}
			return count;
		}
		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);
		}
	}

这里做了两件事：

1. 加载XML中的bean定义，这里使用的是SAX
2. 注册bean定义

	public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
		int countBefore = getRegistry().getBeanDefinitionCount();
        // 注册bean定义
		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
		return getRegistry().getBeanDefinitionCount() - countBefore;
	}

• DefaultBeanDefinitionDocumentReader``registerBeanDefinitions注册bean定义

	@Override
	public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
		this.readerContext = readerContext;
        // 获取Element并注册bean定义
		doRegisterBeanDefinitions(doc.getDocumentElement());
	}

    	protected void doRegisterBeanDefinitions(Element root) {
		// 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 = 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);
				// We cannot use Profiles.of(...) since profile expressions are not supported
				// in XML config. See SPR-12458 for details.
				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;
				}
			}
		}

		preProcessXml(root);
		parseBeanDefinitions(root, this.delegate);
		postProcessXml(root);

		this.delegate = parent;
	}

这里主要做了以下几件事：

1. 获取Element并注册bean定义
2. 解析bean定义前处理
3. 解析bean定义
4. 解析bean定义后处理

核心的方法parseBeanDefinitions：

	protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
        // 判断是否默认命名空间还是自定义命名空间
		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)) {
                        // 解析Spring默认标签
						parseDefaultElement(ele, delegate);
					}
					else {
						delegate.parseCustomElement(ele);
					}
				}
			}
		}
		else {
            // 解析自定义元素节点
			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)) {
			processBeanDefinition(ele, delegate);
		}
		else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
			// recurse
			doRegisterBeanDefinitions(ele);
		}
	}  

parseDefaultElement解析默认Spring标签，分别是import,alias,bean,beans

• 以bean标签为例，看一下如何处理的bean定义

	protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        // 对bean的属性和里面的子元素进行具体解析，并将属性设置到BeanDefinitionHolder中
        // BeanDefinitionHolder是BeanDefinition的封装类，它包含了BeanDefinition
		BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
		if (bdHolder != null) {
			bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
			try {
				// 将BeanDefinition注册到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));
		}
	}

• BeanDefinitionParserDelegate``parseBeanDefinitionElement方法解析并获取AbstractBeanDefinition对象

	@Nullable
	public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
		...省略

		AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
		... 省略
	}

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

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

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

		try {
			AbstractBeanDefinition bd = createBeanDefinition(className, parent);

			parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
			bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));

			parseMetaElements(ele, bd);
			parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
			parseReplacedMethodSubElements(ele, bd.getMethodOverrides());

			parseConstructorArgElements(ele, bd);
			parsePropertyElements(ele, bd);
			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;
	}

• 转到BeanDefinitionReaderUtils.registerBeanDefinition代码

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

		// Register bean definition under primary name.
		String beanName = definitionHolder.getBeanName();
        // DefaultListableBeanFactory registerBeanDefinition方法注册BeanDefinition
		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);
			}
		}
	}

• DefaultListableBeanFactory``registerBeanDefinition方法注册BeanDefinition

	@Override
	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);
			}
		}

		BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
        // 存在BeanDefinition更新beanDefinitionMap
		if (existingDefinition != null) {
			if (!isAllowBeanDefinitionOverriding()) {
				throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
			}
			else if (existingDefinition.getRole() < beanDefinition.getRole()) {
				// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
				if (logger.isInfoEnabled()) {
					logger.info("Overriding user-defined bean definition for bean '" + beanName +
							"' with a framework-generated bean definition: replacing [" +
							existingDefinition + "] with [" + beanDefinition + "]");
				}
			}
			else if (!beanDefinition.equals(existingDefinition)) {
				if (logger.isDebugEnabled()) {
					logger.debug("Overriding bean definition for bean '" + beanName +
							"' with a different definition: replacing [" + existingDefinition +
							"] with [" + beanDefinition + "]");
				}
			}
			else {
				if (logger.isTraceEnabled()) {
					logger.trace("Overriding bean definition for bean '" + beanName +
							"' with an equivalent definition: replacing [" + existingDefinition +
							"] with [" + beanDefinition + "]");
				}
			}
			this.beanDefinitionMap.put(beanName, beanDefinition);
		}
		else {
            // 将beanName和对应的BeanDefinition放到IOC容器的map中
			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<>(this.beanDefinitionNames.size() + 1);
					updatedDefinitions.addAll(this.beanDefinitionNames);
					updatedDefinitions.add(beanName);
					this.beanDefinitionNames = updatedDefinitions;
					removeManualSingletonName(beanName);
				}
			}
			else {
				// Still in startup registration phase
				this.beanDefinitionMap.put(beanName, beanDefinition);
				this.beanDefinitionNames.add(beanName);
				removeManualSingletonName(beanName);
			}
			this.frozenBeanDefinitionNames = null;
		}

		if (existingDefinition != null || containsSingleton(beanName)) {
            // 重新设置beanDefinition 
			resetBeanDefinition(beanName);
		}
		else if (isConfigurationFrozen()) {
			clearByTypeCache();
		}
	}

总结

? ? Spring IOC刷新BeanFactory刷新bean工厂是一个特别复杂的过程，主要是如果已经存在bean工厂就会先销毁并关闭bean工厂，然后重新创建bean工厂加载BeanDefinition，其加载BeanDefinition主要有根据配置的路径和配置资源两种方式进行加载，本文主要讲的是根据配置的路径进行加载。简单来说，根据路径加载BeanDefinition是通过解析XML文件根据文件的Element标签进行加载BeanDefinition，最后就是将BeanDefinition注册到bean工厂并且放到IOC容器的map中。