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SpringFramework之IoC容器初始化

时间:2020-03-30 00:22:08      阅读:60      评论:0      收藏:0      [点我收藏+]

标签:todo   修改   factory   nested   check   dde   stat   this   get   

原创文章,转发请标注https://www.cnblogs.com/boycelee/p/12595884.html

分析例子

启动类

Application,使用的是ClassPathXmlApplicationContext来加载xml文件

/**
 * @author jianw.li
 * @date 2020/3/16 11:53 PM
 * @Description: TODO
 */
public class MyApplication {
    private static final String CONFIG_LOCATION = "classpath:application_context.xml";

    private static final String BEAN_NAME = "hello";

    public static void main(String[] args) {
        ApplicationContext ac = new ClassPathXmlApplicationContext(CONFIG_LOCATION);
        Hello hello = (Hello) ac.getBean(BEAN_NAME);
        hello.sayHello();
    }
}

Bean

/**
 * @author jianw.li
 * @date 2020/3/16 11:53 PM
 * @Description: TODO
 */
public class Hello {

	public void sayHello() {
		System.out.println("Hello World");
	}
}

配置文件

? 在resources下建立名为classpath:application_context.xml的配置文件,并配置好Bean

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	   xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

	<bean id="hello" class="com.boyce.bean.Hello"></bean>

</beans>

总体结构

? ClassPathXmlApplicationContext继承体系如下:

技术图片

? IoC总体结构图如下:

技术图片

源码分析

ClassPathXmlApplicationContext

//构造函数,创建ClassPathXmlApplicationContext,其中configLocation为Bean所在的文件路径
public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
		this(new String[] {configLocation}, true, null);
}

public ClassPathXmlApplicationContext(
			String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
			throws BeansException {
    //null
		super(parent);
    //设置配置路径至ApplicationContext中
		setConfigLocations(configLocations);
		if (refresh) {
      //核心方法,refresh会将旧的ApplicaionContext销毁
			refresh();
		}
	}

AbstractApplicationContext

refresh

? 核心方法,refresh销毁旧ApplicationContext,生成新的ApplicationContext

@Override
	public void refresh() throws BeansException, IllegalStateException {
		//加锁.没有明确对象,只是想让一段代码同步,可以创建Object startupShutdownMonitor = new Object()
		synchronized (this.startupShutdownMonitor) {
			// 为context刷新准备.设置启动时间,设置激活状态等
			prepareRefresh();

			// 告知子类刷新内部bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			prepareBeanFactory(beanFactory);

			try {
				// Allows post-processing of the bean factory in context subclasses.
				postProcessBeanFactory(beanFactory);

				// Invoke factory processors registered as beans in the context.
				invokeBeanFactoryPostProcessors(beanFactory);

				// Register bean processors that intercept bean creation.
				registerBeanPostProcessors(beanFactory);

				// Initialize message source for this context.
				initMessageSource();

				// Initialize event multicaster for this context.
				initApplicationEventMulticaster();

				// Initialize other special beans in specific context subclasses.
				onRefresh();

				// Check for listener beans and register them.
				registerListeners();

				// Instantiate all remaining (non-lazy-init) singletons.
				//初始化所有未懒加载单例
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				//广播初始化完成
				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.
				destroyBeans();

				// Reset ‘active‘ flag.
				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...
				resetCommonCaches();
			}
		}
	}
obtainFreshBeanFactory

? 告知子类刷新内部bean factory.

? 核心方法,初始化BeanFactory、加载Bean、注册Bean

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
		//刷新Bean工厂,关闭并销毁旧BeanFacroty
		refreshBeanFactory();
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		if (logger.isDebugEnabled()) {
			logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
		}
		return beanFactory;
	}
refreshBeanFactory

? 关闭并销毁旧BeanFactory,创建与初始化新BeanFactory。为什么是DefaultListableBeanFactory?

@Override
	protected final void refreshBeanFactory() throws BeansException {
		if (hasBeanFactory()) {
			destroyBeans();
			closeBeanFactory();
		}
		try {
			//初始化DefaultListableBeanFactory,为什么选择实例化DefaultListableBeanFactory?而不是其他的Bean工厂
			DefaultListableBeanFactory beanFactory = createBeanFactory();
			//Bean工厂序列化设置id
			beanFactory.setSerializationId(getId());
			//定制Bean工厂,设置不允许覆盖Bean,不允许循环依赖等
			customizeBeanFactory(beanFactory);
			//将Bean加载至Bean工厂中
			loadBeanDefinitions(beanFactory);
			//此处synchronized块与#hasBeanFactory中的synchronized块存在关联,此处锁住之后hasBeanFactory中的synchronized块将等待
			//避免beanFactory未销毁或未关闭的情况
			synchronized (this.beanFactoryMonitor) {
				this.beanFactory = beanFactory;
			}
		}
		catch (IOException ex) {
			throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
		}
	}
customizeBeanFactory

? 定制BeanFactory。设置Bean覆盖、循环依赖等。什么是循环依赖?

protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) {
		if (this.allowBeanDefinitionOverriding != null) {
			//默认值为false不允许对Bean进行覆盖
			beanFactory.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
		}
		if (this.allowCircularReferences != null) {
			//默认值为false,不允许循环依赖
			beanFactory.setAllowCircularReferences(this.allowCircularReferences);
		}
	}

AbstractXmlApplicationContext

loadBeanDefinitions
@Override
	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.
		beanDefinitionReader.setEnvironment(this.getEnvironment());
		beanDefinitionReader.setResourceLoader(this);
		beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

		// Allow a subclass to provide custom initialization of the reader,
		// then proceed with actually loading the bean definitions.
		initBeanDefinitionReader(beanDefinitionReader);
		loadBeanDefinitions(beanDefinitionReader);
	}
loadBeanDefinitions
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
		Resource[] configResources = getConfigResources();
		if (configResources != null) {
			//加载资源对象,最终还是会回到这种方式去加载bean.
			reader.loadBeanDefinitions(configResources);
		}
		String[] configLocations = getConfigLocations();
		if (configLocations != null) {
			//加载资源路径吗
			reader.loadBeanDefinitions(configLocations);
		}
	}

AbstractBeanDefinitionReader

loadBeanDefinitions
@Override
	public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
		Assert.notNull(locations, "Location array must not be null");
		int counter = 0;
		//循环配置文件路径
		for (String location : locations) {
			counter += loadBeanDefinitions(location);
		}
		return counter;
	}
public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
		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 {
        // 将xml转为Resource,所以上面的两种资源加载方式,最终都会回到Resource为参数的加载方式
				Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
				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;
		}
	}
@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;
	}

XmlBeanDefinitionReader

loadBeanDefinitions

? 从详细的XML文件中加载Bean

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());
		}

		//用于存储编译过的Reource
		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 {
			InputStream inputStream = encodedResource.getResource().getInputStream();
			try {
				InputSource inputSource = new InputSource(inputStream);
				if (encodedResource.getEncoding() != null) {
					inputSource.setEncoding(encodedResource.getEncoding());
				}
				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();
			}
		}
	}
doLoadBeanDefinitions

? 从xml文件中加载bean,将xml转为Document并注册Bean

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
			throws BeanDefinitionStoreException {
		try {
			//将xml转为Document
			Document doc = doLoadDocument(inputSource, resource);
			//注册Bean
			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);
		}
	}
registerBeanDefinitions

? 计算从当前配置文件中加载bean的数量

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

DefaultBeanDefinitionDocumentReader

registerBeanDefinitions

? 从“spring-beans” xsd中解析bean。什么是xsd?XML结构定义 ( XML Schemas Definition)

@Override
	public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
		this.readerContext = readerContext;
		logger.debug("Loading bean definitions");
		Element root = doc.getDocumentElement();
		doRegisterBeanDefinitions(root);
	}
doRegisterBeanDefinitions

? 从根节点开始注册每一个Bean

/**
	 * Register each bean definition within the given root {@code <beans/>} element.
	 * 从根节点开始注册每一个Bean
	 */
	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.
		//可以通过spring.profiles.active设定当前环境激活的profile,例如配置prod,可以通过@ActiveProfiles配置

		//解析bean定义
		BeanDefinitionParserDelegate parent = this.delegate;
		this.delegate = createDelegate(getReaderContext(), root, parent);

		if (this.delegate.isDefaultNamespace(root)) {
			//获取元素中profile属性,可以通过xml或@Profile设置当前bean所属的profile
			String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
			//不能做profile属性则直接跳过
			if (StringUtils.hasText(profileSpec)) {
				//配置多profile
				String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
						profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
				//元素中的profile是否是环境指定的profiles之一
				if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
					if (logger.isInfoEnabled()) {
						logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec +
								"] not matching: " + getReaderContext().getResource());
					}
					//不在当前环境指定的profile中则return
					return;
				}
			}
		}

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

		this.delegate = parent;
	}
parseBeanDefinitions

? 从文档根节点开始解析元素,import、alias、bean等

/**
	 * Parse the elements at the root level in the document:
	 * "import", "alias", "bean".
	 * @param root the DOM root element of the document
	 */
	protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
		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default namespace下的元素(例如:<import>、<alias>、<beans>、<bean>)
						parseDefaultElement(ele, delegate);
					}
					else {
						//解析Custom元素(例如:<mvc>、<context>、<aop>)
						delegate.parseCustomElement(ele);
					}
				}
			}
		}
		else {
			delegate.parseCustomElement(root);
		}
	}
parseDefaultElement

? 解析default namespace下的元素(例如:

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)) {
			//了解bean解析源码
			processBeanDefinition(ele, delegate);
		}
		else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
			// recurse
			doRegisterBeanDefinitions(ele);
		}
	}
processBeanDefinition

? 获取bean元素解析并注册

/**
	 * Process the given bean element, parsing the bean definition
	 * and registering it with the registry.
	 * 获取bean元素解析并注册
	 */
	protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
		//解析bean元素并封装至BeanDefinitionHolder
		BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
		if (bdHolder != null) {
			bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
			try {
				// Register the final decorated instance.
				//注册装饰的实例
				BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
			}
			catch (BeanDefinitionStoreException ex) {
				getReaderContext().error("Failed to register bean definition with name ‘" +
						bdHolder.getBeanName() + "‘", ele, ex);
			}
			// Send registration event.
			//发送注册事件
			getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
		}

DefaultListableBeanFactory

registerBeanDefinition
@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 oldBeanDefinition;
		//beanDefinitionMap放置所有注册的Bean
		oldBeanDefinition = this.beanDefinitionMap.get(beanName);

		//如果bean名已存在
		if (oldBeanDefinition != null) {
			//不允许覆盖bean
			if (!isAllowBeanDefinitionOverriding()) {
				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Cannot register bean definition [" + beanDefinition + "] for bean ‘" + beanName +
						"‘: There is already [" + oldBeanDefinition + "] bound.");
			}
			//通过比较BeanRole.判断谁覆盖谁
			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 + "]");
				}
			}
			//新bean覆盖旧bean
			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 + "]");
				}
			}
			//将bean放置beanDefinitionMap中
			this.beanDefinitionMap.put(beanName, beanDefinition);
		}
		//beanName没有与beanDefinitionMap中的重复
		else {
			//非正常情况下,其他的Bean已经初始化,如果已经有bean初始化,则使用者已经在进行业务操作,无法保证对beanDefinitionMap、beanDefinitionNames、manualSingletonNames进行操作的一些列动作的线程安全,所以需要加锁。参考:https://blog.csdn.net/qq_41907991/article/details/97614337
			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;
					if (this.manualSingletonNames.contains(beanName)) {
						Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
						updatedSingletons.remove(beanName);
						this.manualSingletonNames = updatedSingletons;
					}
				}
			}
			else {
				// Still in startup registration phase
				//bean放置beanDefinitionMap中
				this.beanDefinitionMap.put(beanName, beanDefinition);
				//记录bean名称
				this.beanDefinitionNames.add(beanName);
				//bean不需要手动注册
				this.manualSingletonNames.remove(beanName);
			}
			this.frozenBeanDefinitionNames = null;
		}

		if (oldBeanDefinition != null || containsSingleton(beanName)) {
			resetBeanDefinition(beanName);
		}
	}

调用关系

? 技术图片

总结

? 至此已经完成了IoC容器的初始化。将xml文件中的bean元素解析为Bean,将Bean注册至注册中心,并发送注册事件。DefaultListableBeanFactory建立Bean配置信息,这些信息都存放在BeanDefinitionMap中,由IoC容器来维护。

? 最后,懂得不多,做得很少。文章肯定又不少错误,如大家发现麻烦及时指出,为了避免误导更多人,我也会及时学习并修改!

引用参考

[1]《Spring技术内幕》

[2]https://www.javadoop.com/post/spring-ioc

[3]https://github.com/seaswalker/spring-analysis/blob/master/note/Spring.md#classpathxmlapplicationcontext

原创文章,转发请标注https://www.cnblogs.com/boycelee/p/12595884.html

SpringFramework之IoC容器初始化

标签:todo   修改   factory   nested   check   dde   stat   this   get   

原文地址:https://www.cnblogs.com/boycelee/p/12595884.html

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