【spring5源码分析】IoC部分

Alan 312 2019-07-08
定位阶段

​ 1. 构造器中初始化。

	public ClassPathXmlApplicationContext(
			String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
			throws BeansException {

		super(parent);
		setConfigLocations(configLocations);
		if (refresh) {
			refresh();
		}
	}
  1. 调用 setConfigLocations(),解析定义资源文件的路径,将其保存到字符串数组。
	//解析Bean定义资源文件的路径,处理多个资源文件字符串数组
	public void setConfigLocations(@Nullable String... locations) {
		if (locations != null) {
			Assert.noNullElements(locations, "Config locations must not be null");
			this.configLocations = new String[locations.length];
			for (int i = 0; i < locations.length; i++) {
				// resolvePath为同一个类中将字符串解析为路径的方法
				this.configLocations[i] = resolvePath(locations[i]).trim();
			}
		}
		else {
			this.configLocations = null;
		}
	}
  1. 调用 refresh(),启动容器。
	@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			//1、调用容器准备刷新的方法,获取容器的当时时间,同时给容器设置同步标识
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			//2、告诉子类启动refreshBeanFactory()方法,Bean定义资源文件的载入从
			//子类的refreshBeanFactory()方法启动
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			//3、为BeanFactory配置容器特性,例如类加载器、事件处理器等
			prepareBeanFactory(beanFactory);

			try {
				// Allows post-processing of the bean factory in context subclasses.
				//4、为容器的某些子类指定特殊的BeanPost事件处理器
				postProcessBeanFactory(beanFactory);

				// Invoke factory processors registered as beans in the context.
				//5、调用所有注册的BeanFactoryPostProcessor的Bean
				invokeBeanFactoryPostProcessors(beanFactory);

				// Register bean processors that intercept bean creation.
				//6、为BeanFactory注册BeanPost事件处理器.
				//BeanPostProcessor是Bean后置处理器,用于监听容器触发的事件
				registerBeanPostProcessors(beanFactory);

				// Initialize message source for this context.
				//7、初始化信息源,和国际化相关.
				initMessageSource();

				// Initialize event multicaster for this context.
				//8、初始化容器事件传播器.
				initApplicationEventMulticaster();

				// Initialize other special beans in specific context subclasses.
				//9、调用子类的某些特殊Bean初始化方法
				onRefresh();

				// Check for listener beans and register them.
				//10、为事件传播器注册事件监听器.
				registerListeners();

				// Instantiate all remaining (non-lazy-init) singletons.
				//11、初始化所有剩余的单例Bean
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				//12、初始化容器的生命周期事件处理器,并发布容器的生命周期事件
				finishRefresh();
			}

			catch (BeansException ex) {
				if (logger.isWarnEnabled()) {
					logger.warn("Exception encountered during context initialization - " +
							"cancelling refresh attempt: " + ex);
				}

				// Destroy already created singletons to avoid dangling resources.
				//13、销毁已创建的Bean
				destroyBeans();

				// Reset 'active' flag.
				//14、取消refresh操作,重置容器的同步标识。
				cancelRefresh(ex);

				// Propagate exception to caller.
				throw ex;
			}

			finally {
				// Reset common introspection caches in Spring's core, since we
				// might not ever need metadata for singleton beans anymore...
				//15、重设公共缓存
				resetCommonCaches();
			}
		}
	}
  1. 在 refresh() 中,调用 AbstractApplicationContext 类的 obtainFreshBeanFactory() 方法。
	protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
		//这里使用了委派设计模式,父类定义了抽象的refreshBeanFactory()方法,具体实现调用子类容器的refreshBeanFactory()方法
		refreshBeanFactory();
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		if (logger.isDebugEnabled()) {
			logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
		}
		return beanFactory;
	}
  1. 使用委派模式,在子类中调用 refreshBeanFactory() 方法,启动beanFactory。
	@Override
	protected final void refreshBeanFactory() throws BeansException {
		//如果已经有容器,销毁容器中的bean,关闭容器
		if (hasBeanFactory()) {
			destroyBeans();
			closeBeanFactory();
		}
		try {
			//创建IOC容器
			DefaultListableBeanFactory beanFactory = createBeanFactory();
			beanFactory.setSerializationId(getId());
			//对IOC容器进行定制化,如设置启动参数,开启注解的自动装配等
			customizeBeanFactory(beanFactory);
			//调用载入Bean定义的方法,主要这里又使用了一个委派模式,在当前类中只定义了抽象的loadBeanDefinitions方法,具体的实现调用子类容器
			loadBeanDefinitions(beanFactory);
			synchronized (this.beanFactoryMonitor) {
				this.beanFactory = beanFactory;
			}
		}
		catch (IOException ex) {
			throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
		}
	}
加载阶段
  1. 使用委派模式,调用 loadBeanDefinitions() 方法。
	//实现父类抽象的载入Bean定义方法
	@Override
	protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
		// Create a new XmlBeanDefinitionReader for the given BeanFactory.
		//创建XmlBeanDefinitionReader,即创建Bean读取器,并通过回调设置到容器中去,容  器使用该读取器读取Bean定义资源
		XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

		// Configure the bean definition reader with this context's
		// resource loading environment.
		//为Bean读取器设置Spring资源加载器,AbstractXmlApplicationContext的
		//祖先父类AbstractApplicationContext继承DefaultResourceLoader,因此,容器本身也是一个资源加载器
		beanDefinitionReader.setEnvironment(this.getEnvironment());
		beanDefinitionReader.setResourceLoader(this);
		//为Bean读取器设置SAX xml解析器
		beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

		// Allow a subclass to provide custom initialization of the reader,
		// then proceed with actually loading the bean definitions.
		//当Bean读取器读取Bean定义的Xml资源文件时,启用Xml的校验机制
		initBeanDefinitionReader(beanDefinitionReader);
		//Bean读取器真正实现加载的方法
		loadBeanDefinitions(beanDefinitionReader);
	}
  1. 调用自己的 loadBeanDefinitions() 方法。
	protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
		//获取Bean定义资源的定位
		Resource[] configResources = getConfigResources();
		if (configResources != null) {
			//Xml Bean读取器调用其父类AbstractBeanDefinitionReader读取定位
			//的Bean定义资源
			reader.loadBeanDefinitions(configResources);
		}
		//如果子类中获取的Bean定义资源定位为空,则获取FileSystemXmlApplicationContext构造方法中setConfigLocations方法设置的资源
		String[] configLocations = getConfigLocations();
		if (configLocations != null) {
			//Xml Bean读取器调用其父类AbstractBeanDefinitionReader读取定位
			//的Bean定义资源
			reader.loadBeanDefinitions(configLocations);
		}
	}
  1. 调用 AbstractBeanDefinitionReader 类的 loadBeanDefinitions() 方法。
	@Override
	public int loadBeanDefinitions(Resource... resources) throws BeanDefinitionStoreException {
		Assert.notNull(resources, "Resource array must not be null");
		int counter = 0;
		for (Resource resource : resources) {
			counter += loadBeanDefinitions(resource);
		}
		return counter;
	}
  1. 调用 XmlBeanDefinitionReader 类的 loadBeanDefinitions() 方法。
	//这里是载入XML形式Bean定义资源文件方法
	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<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 {
			//将资源文件转为InputStream的IO流
			InputStream inputStream = encodedResource.getResource().getInputStream();
			try {
				//从InputStream中得到XML的解析源
				InputSource inputSource = new InputSource(inputStream);
				if (encodedResource.getEncoding() != null) {
					inputSource.setEncoding(encodedResource.getEncoding());
				}
				//这里是具体的读取过程
				return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
			}
			finally {
				//关闭从Resource中得到的IO流
				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();
			}
		}
	}
  1. 调用自己的 doLoadBeanDefinitions() 方法。
	//从特定XML文件中实际载入Bean定义资源的方法
	protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
			throws BeanDefinitionStoreException {
		try {
			//将XML文件转换为DOM对象,解析过程由documentLoader实现
			Document doc = doLoadDocument(inputSource, resource);
			//这里是启动对Bean定义解析的详细过程,该解析过程会用到Spring的Bean配置规则
			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);
		}
	}
  1. 调用自己的 registerBeanDefinitions() 方法。
	//按照Spring的Bean语义要求将Bean定义资源解析并转换为容器内部数据结构
	public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
		//得到BeanDefinitionDocumentReader来对xml格式的BeanDefinition解析
		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
		//获得容器中注册的Bean数量
		int countBefore = getRegistry().getBeanDefinitionCount();
		//解析过程入口,这里使用了委派模式,BeanDefinitionDocumentReader只是个接口,
		//具体的解析实现过程有实现类DefaultBeanDefinitionDocumentReader完成
		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
		//统计解析的Bean数量
		return getRegistry().getBeanDefinitionCount() - countBefore;
	}
  1. 调用 DefaultBeanDefinitionDocumentReader 类的 registerBeanDefinitions() 方法,根据Spring DTD对Bean的定义规则解析Bean定义Document对象。
	@Override
	public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
		//获得XML描述符
		this.readerContext = readerContext;
		logger.debug("Loading bean definitions");
		//获得Document的根元素
		Element root = doc.getDocumentElement();
		doRegisterBeanDefinitions(root);
	}
  1. 调用自己的 doRegisterBeanDefinitions() 方法。注册beanDefinition。
	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.

		//具体的解析过程由BeanDefinitionParserDelegate实现,
		//BeanDefinitionParserDelegate中定义了Spring Bean定义XML文件的各种元素
		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)) {
					if (logger.isInfoEnabled()) {
						logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec +
								"] not matching: " + getReaderContext().getResource());
					}
					return;
				}
			}
		}

		//在解析Bean定义之前,进行自定义的解析,增强解析过程的可扩展性
		preProcessXml(root);
		//从Document的根元素开始进行Bean定义的Document对象
		parseBeanDefinitions(root, this.delegate);
		//在解析Bean定义之后,进行自定义的解析,增加解析过程的可扩展性
		postProcessXml(root);

		this.delegate = parent;
	}
注册阶段
  1. 调用 DefaultBeanDefinitionDocumentReader 类的 parseBeanDefinitions() 方法。
	/**
	 * Process the given bean element, parsing the bean definition
	 * and registering it with the registry.
	 */
	//解析Bean定义资源Document对象的普通元素
	protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
		BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
		// BeanDefinitionHolder是对BeanDefinition的封装,即Bean定义的封装类
		//对Document对象中<Bean>元素的解析由BeanDefinitionParserDelegate实现
		// BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
		if (bdHolder != null) {
			bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
			try {
				// Register the final decorated instance.
				//向Spring IOC容器注册解析得到的Bean定义,这是Bean定义向IOC容器注册的入口
				BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
			}
			catch (BeanDefinitionStoreException ex) {
				getReaderContext().error("Failed to register bean definition with name '" +
						bdHolder.getBeanName() + "'", ele, ex);
			}
			// Send registration event.
			//在完成向Spring IOC容器注册解析得到的Bean定义之后,发送注册事件
			getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
		}
	}
  1. 调用 BeanDefinitionReaderUtils 的 registerBeanDefinition() 方法,将解析的BeanDefinitionHold注册到容器中。
	//将解析的BeanDefinitionHold注册到容器中
	public static void registerBeanDefinition(
			BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
			throws BeanDefinitionStoreException {

		// Register bean definition under primary name.
		//获取解析的BeanDefinition的名称
		String beanName = definitionHolder.getBeanName();
		//向IOC容器注册BeanDefinition
		registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

		// Register aliases for bean name, if any.
		//如果解析的BeanDefinition有别名,向容器为其注册别名
		String[] aliases = definitionHolder.getAliases();
		if (aliases != null) {
			for (String alias : aliases) {
				registry.registerAlias(beanName, alias);
			}
		}
	}
  1. 向IoC容器注册BeanDefinition,将注册信息存入beanDefinitionMap 中
	//向IOC容器注册解析的BeanDefiniton
	@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");

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

		BeanDefinition oldBeanDefinition;

		oldBeanDefinition = this.beanDefinitionMap.get(beanName);

		if (oldBeanDefinition != null) {
			if (!isAllowBeanDefinitionOverriding()) {
				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
						"': There is already [" + oldBeanDefinition + "] bound.");
			}
			else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
				// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
				if (this.logger.isWarnEnabled()) {
					this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +
							"' with a framework-generated bean definition: replacing [" +
							oldBeanDefinition + "] with [" + beanDefinition + "]");
				}
			}
			else if (!beanDefinition.equals(oldBeanDefinition)) {
				if (this.logger.isInfoEnabled()) {
					this.logger.info("Overriding bean definition for bean '" + beanName +
							"' with a different definition: replacing [" + oldBeanDefinition +
							"] with [" + beanDefinition + "]");
				}
			}
			else {
				if (this.logger.isDebugEnabled()) {
					this.logger.debug("Overriding bean definition for bean '" + beanName +
							"' with an equivalent definition: replacing [" + oldBeanDefinition +
							"] with [" + beanDefinition + "]");
				}
			}
			this.beanDefinitionMap.put(beanName, beanDefinition);
		}
		else {
			if (hasBeanCreationStarted()) {
				// Cannot modify startup-time collection elements anymore (for stable iteration)
				//注册的过程中需要线程同步,以保证数据的一致性
				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;
					if (this.manualSingletonNames.contains(beanName)) {
						Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
						updatedSingletons.remove(beanName);
						this.manualSingletonNames = updatedSingletons;
					}
				}
			}
			else {
				// Still in startup registration phase
				this.beanDefinitionMap.put(beanName, beanDefinition);
				this.beanDefinitionNames.add(beanName);
				this.manualSingletonNames.remove(beanName);
			}
			this.frozenBeanDefinitionNames = null;
		}

		//检查是否有同名的BeanDefinition已经在IOC容器中注册
		if (oldBeanDefinition != null || containsSingleton(beanName)) {
			//重置所有已经注册过的BeanDefinition的缓存
			resetBeanDefinition(beanName);
		}
	}

# Spring