Spring-Bean的加載

    我們先用xml加載的方式看下spring bean加載的整個過程。

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.2.xsd">
    <!-- 使用設值注入方式裝配Person實例 -->
    <bean id="person" class="com.example.demo.beans.Person">
        <property name="name" value="zhangsan"/>
        <property name="age" value="20"/>
    </bean>
</beans>

ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:spring-beans.xml");

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

		super(parent);
		setConfigLocations(configLocations);
		if (refresh) {
			refresh();
		}
}

    通過指定的parent ApplicationContext（這裏爲空）創建一個ClassPathXmlApplicationContext，configLocations即爲“classpath:spring-beans.xml”，refresh爲true。setConfigLocations主要將configLocations賦值給AbstractRefreshableConfigApplicationContext，後面解析xml文件時會從這裏來取文件路徑。

      refresh()方法是本篇Bean加載核心方法，先看下refresh內部的主要方法。

	public void refresh() throws BeansException, IllegalStateException {
        // private final Object startupShutdownMonitor = new Object();
        // 創建了一個對象專門作爲容器的刷新（refresh）和銷燬（destroy）的同步鎖
		synchronized (this.startupShutdownMonitor) {
			// refresh的前置準備，這裏主要是爲ApplicationContext的成員變量做默認的賦值操作
			prepareRefresh();

			// 創建BeanFactory，並解析xml配置文件定義bean，核心方法，後面做詳細介紹
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// BeanFactory的前置準備
			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.
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				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();
			}
		}
}

一、BeanFactory的創建

ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

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

@Override
	protected final void refreshBeanFactory() throws BeansException {
        // 通過同步鎖Object beanFactoryMonitor = new Object()判斷BeanFactory是否爲null
		if (hasBeanFactory()) {
            // 如果BeanFactory當前不爲null，先銷燬和關閉BeanFactory
			destroyBeans();
			closeBeanFactory();
		}
		try {
            // 創建一個DefaultListableBeanFactory，記住這個BeanFactory
			DefaultListableBeanFactory beanFactory = createBeanFactory();
			beanFactory.setSerializationId(getId());
            // 給兩個成員變量賦值
            // allowBeanDefinitionOverriding=true 允許BeanDefinition重寫
            // allowCircularReferences=true 允許循環依賴
			customizeBeanFactory(beanFactory);
            // 加載和解析配置文件，創建BeanDefinition，重要方法
			loadBeanDefinitions(beanFactory);
			synchronized (this.beanFactoryMonitor) {
				this.beanFactory = beanFactory;
			}
		}
		catch (IOException ex) {
			throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
		}
}

@Override
	protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
		// 創建XmlBeanDefinitionReader解析xml文件
		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);
        // 重要，加載BeanDefinition
		loadBeanDefinitions(beanDefinitionReader);
	}

    解析xml這裏用了一系列的loadBeanDefinitions重載方法，這裏不一一看了，直接看最後解析的過程。

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 == 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 {
            // EncodedResource加載了spring-beans.xml
			InputStream inputStream = encodedResource.getResource().getInputStream();
			try {
				InputSource inputSource = new InputSource(inputStream);
				if (encodedResource.getEncoding() != null) {
					inputSource.setEncoding(encodedResource.getEncoding());
				}
                // 從inputStream中解析創建BeanDefinition，重要
				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();
			}
		}
}

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

		try {
            // 解析xml獲取的Document
			Document doc = doLoadDocument(inputSource, resource);
            // 從Document中獲取數據註冊BeanDefinition
			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);
		}
	}

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

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)) {
                        // 解析默認xml標籤元素
						parseDefaultElement(ele, delegate);
					}
					else {
                        // 解析自定義標籤元素
						delegate.parseCustomElement(ele);
					}
				}
			}
		}
		else {
			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)) {
            // 這裏我們主要看解析xml中Bean標籤元素
			processBeanDefinition(ele, delegate);
		}
		else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
			// recurse
			doRegisterBeanDefinitions(ele);
		}
}

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
		BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
		if (bdHolder != null) {
			bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
			try {
				// Register the final decorated instance.
				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));
		}
}

    這裏主要分爲三步：

• BeanDefinitionParserDelegate.parseBeanDefinitionElement(ele)
• BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());

delegate.parseBeanDefinitionElement(ele)

BeanDefinitionParserDelegate中包含xml bean節點中的各個元素，主要用於xml中bean節點的解析，然後創建BeanDefinition。

@Nullable
	public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
        // 獲取id元素的值
		String id = ele.getAttribute(ID_ATTRIBUTE);
        // 獲取name元素的值
		String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
        // 處理別名
		List<String> aliases = new ArrayList<>();
		if (StringUtils.hasLength(nameAttr)) {
			String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
			aliases.addAll(Arrays.asList(nameArr));
		}

		String beanName = id;
		if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
            // 如果id爲空，但是有別名，beanName就爲別名
			beanName = aliases.remove(0);
			if (logger.isTraceEnabled()) {
				logger.trace("No XML 'id' specified - using '" + beanName +
						"' as bean name and " + aliases + " as aliases");
			}
		}

		if (containingBean == null) {
            // 判斷beanName和別名是否已存在，如果存在就報錯否則加入到usedNames集合用於其他beanName的唯一性判斷
			checkNameUniqueness(beanName, aliases, ele);
		}

        // 創建BeanDefinition
		AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
		if (beanDefinition != null) {
			if (!StringUtils.hasText(beanName)) {
				try {
					if (containingBean != null) {
						beanName = BeanDefinitionReaderUtils.generateBeanName(
								beanDefinition, this.readerContext.getRegistry(), true);
					}
					else {
						beanName = this.readerContext.generateBeanName(beanDefinition);
						// Register an alias for the plain bean class name, if still possible,
						// if the generator returned the class name plus a suffix.
						// This is expected for Spring 1.2/2.0 backwards compatibility.
						String beanClassName = beanDefinition.getBeanClassName();
						if (beanClassName != null &&
								beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
								!this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
							aliases.add(beanClassName);
						}
					}
					if (logger.isTraceEnabled()) {
						logger.trace("Neither XML 'id' nor 'name' specified - " +
								"using generated bean name [" + beanName + "]");
					}
				}
				catch (Exception ex) {
					error(ex.getMessage(), ele);
					return null;
				}
			}
			String[] aliasesArray = StringUtils.toStringArray(aliases);
            // 通過BeanDefinition創建BeanDefinitionHolder
			return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
		}

		return null;
}

    在看上面這個方法中具體創建BeanDefinition的過程。

@Nullable
	public AbstractBeanDefinition parseBeanDefinitionElement(
			Element ele, String beanName, @Nullable BeanDefinition containingBean) {
        // 根據BeanName創建了一個BeanEntry放到了LikedList中
		this.parseState.push(new BeanEntry(beanName));

		String className = null;
        // 獲取class元素的值
		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 {
            // 創建BeanDefinition 
			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;
}


// parseState.push
public final class ParseState {

	/**
	 * 內部有一個LinkedList，Entry的實現類有BeanEntry
     * 對外的push/pop/peek都有內部的這個LinkedList實現。
	 */
	private final LinkedList<Entry> state;
}

// BeanEntry
public class BeanEntry implements ParseState.Entry {

	private String beanDefinitionName;

}


// 使用BeanDefinitionReaderUtils創建BeanDefinition
public static AbstractBeanDefinition createBeanDefinition(
			@Nullable String parentName, @Nullable String className, @Nullable ClassLoader classLoader) throws ClassNotFoundException {

		GenericBeanDefinition bd = new GenericBeanDefinition();
		bd.setParentName(parentName);
		if (className != null) {
			if (classLoader != null) {
				bd.setBeanClass(ClassUtils.forName(className, classLoader));
			}
			else {
				bd.setBeanClassName(className);
			}
		}
		return bd;
}


// 解析xml bean中的其他元素
public AbstractBeanDefinition parseBeanDefinitionAttributes(Element ele, String beanName,
			@Nullable BeanDefinition containingBean, AbstractBeanDefinition bd) {
		if (ele.hasAttribute(SINGLETON_ATTRIBUTE)) {
            // 1.X版本設置單例Bean，告警
			error("Old 1.x 'singleton' attribute in use - upgrade to 'scope' declaration", ele);
		}
		else if (ele.hasAttribute(SCOPE_ATTRIBUTE)) {
            // 設置scope，有singleton(單例Bean)/prototype(原型Bean)/request/session，後兩種web中使用
			bd.setScope(ele.getAttribute(SCOPE_ATTRIBUTE));
		}
		else if (containingBean != null) {
			// Take default from containing bean in case of an inner bean definition.
			bd.setScope(containingBean.getScope());
		}

		if (ele.hasAttribute(ABSTRACT_ATTRIBUTE)) {
			bd.setAbstract(TRUE_VALUE.equals(ele.getAttribute(ABSTRACT_ATTRIBUTE)));
		}
        // 是否懶加載
		String lazyInit = ele.getAttribute(LAZY_INIT_ATTRIBUTE);
		if (isDefaultValue(lazyInit)) {
			lazyInit = this.defaults.getLazyInit();
		}
		bd.setLazyInit(TRUE_VALUE.equals(lazyInit));

        // 自動注入的方式，比如byName/byType
		String autowire = ele.getAttribute(AUTOWIRE_ATTRIBUTE);
		bd.setAutowireMode(getAutowireMode(autowire));
        // 依賴bean depends-on元素設置的值
		if (ele.hasAttribute(DEPENDS_ON_ATTRIBUTE)) {
			String dependsOn = ele.getAttribute(DEPENDS_ON_ATTRIBUTE);
			bd.setDependsOn(StringUtils.tokenizeToStringArray(dependsOn, MULTI_VALUE_ATTRIBUTE_DELIMITERS));
		}

		String autowireCandidate = ele.getAttribute(AUTOWIRE_CANDIDATE_ATTRIBUTE);
		if (isDefaultValue(autowireCandidate)) {
			String candidatePattern = this.defaults.getAutowireCandidates();
			if (candidatePattern != null) {
				String[] patterns = StringUtils.commaDelimitedListToStringArray(candidatePattern);
				bd.setAutowireCandidate(PatternMatchUtils.simpleMatch(patterns, beanName));
			}
		}
		else {
			bd.setAutowireCandidate(TRUE_VALUE.equals(autowireCandidate));
		}
        // primary元素
		if (ele.hasAttribute(PRIMARY_ATTRIBUTE)) {
			bd.setPrimary(TRUE_VALUE.equals(ele.getAttribute(PRIMARY_ATTRIBUTE)));
		}

		if (ele.hasAttribute(INIT_METHOD_ATTRIBUTE)) {
			String initMethodName = ele.getAttribute(INIT_METHOD_ATTRIBUTE);
			bd.setInitMethodName(initMethodName);
		}
		else if (this.defaults.getInitMethod() != null) {
			bd.setInitMethodName(this.defaults.getInitMethod());
			bd.setEnforceInitMethod(false);
		}

		if (ele.hasAttribute(DESTROY_METHOD_ATTRIBUTE)) {
			String destroyMethodName = ele.getAttribute(DESTROY_METHOD_ATTRIBUTE);
			bd.setDestroyMethodName(destroyMethodName);
		}
		else if (this.defaults.getDestroyMethod() != null) {
			bd.setDestroyMethodName(this.defaults.getDestroyMethod());
			bd.setEnforceDestroyMethod(false);
		}

		if (ele.hasAttribute(FACTORY_METHOD_ATTRIBUTE)) {
			bd.setFactoryMethodName(ele.getAttribute(FACTORY_METHOD_ATTRIBUTE));
		}
		if (ele.hasAttribute(FACTORY_BEAN_ATTRIBUTE)) {
			bd.setFactoryBeanName(ele.getAttribute(FACTORY_BEAN_ATTRIBUTE));
		}

		return bd;
}

BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());

將BeanDefinition註冊到BeanDefinitionMap中。

public static void registerBeanDefinition(
			BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
			throws BeanDefinitionStoreException {
		String beanName = definitionHolder.getBeanName();
        // 通過beanName註冊BeanDefinition,其實就是註冊到BeanDefinitionMap中
		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);
			}
		}
}

@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);
			}
		}
        // 判斷BeanDefinitionMap中是否存在，如果存在就報錯
		BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
		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 {
            // 如果BeanDefinitionMap中不存在，註冊
            // 判斷bean是否開始創建，此時還沒有開始創建，爲false
			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 {
				// 註冊到BeanDefinitionMap中
				this.beanDefinitionMap.put(beanName, beanDefinition);
				this.beanDefinitionNames.add(beanName);
				this.manualSingletonNames.remove(beanName);
			}
			this.frozenBeanDefinitionNames = null;
		}

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

至此，refresh方法中的obtainFreshBeanFactory()方法執行完成。

二、BeanFactory的前置準備，初始賦值

prepareBeanFactory(beanFactory);

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
		// Tell the internal bean factory to use the context's class loader etc.
		beanFactory.setBeanClassLoader(getClassLoader());
		beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
		beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

		// Configure the bean factory with context callbacks.
		beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
		beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
		beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
		beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
		beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
		beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
		beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

		// BeanFactory interface not registered as resolvable type in a plain factory.
		// MessageSource registered (and found for autowiring) as a bean.
		beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
		beanFactory.registerResolvableDependency(ResourceLoader.class, this);
		beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
		beanFactory.registerResolvableDependency(ApplicationContext.class, this);

		// Register early post-processor for detecting inner beans as ApplicationListeners.
		beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

		// Detect a LoadTimeWeaver and prepare for weaving, if found.
		if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
			beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
			// Set a temporary ClassLoader for type matching.
			beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
		}

		// Register default environment beans.
		if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
			beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
		}
		if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
			beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
		}
		if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
			beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
		}
}

三、BeanFactory的後置處理

postProcessBeanFactory(beanFactory);

該方法默認沒有實現，這裏是留的擴展點，可以實現BeanFactoryPostProcessor去擴展。

四、執行BeanFactoryPostProcessor

invokeBeanFactoryPostProcessors(beanFactory);

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        // 執行ApplicationContext中的所有BeanFactoryProcessor
		PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

		if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
			beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
			beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
		}
}


獲取ApplicationContext中的BeanFactoryPostProcessor
public List<BeanFactoryPostProcessor> getBeanFactoryPostProcessors() {
		return this.beanFactoryPostProcessors;
}

五、註冊BeanPostProcessor

registerBeanPostProcessors(beanFactory);

六、國際化

initMessageSource();

七、初始化事件監聽多路廣播器

initApplicationEventMulticaster();

八、onRefresh

這個方法是空的。解釋是在特定的上下文中初始化特別的beans。可以看到其也是用於初始化的。

九、註冊監聽器

registerListeners();

十、實例化所有剩餘的非懶加載單例 bean

finishBeanFactoryInitialization(beanFactory);

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
		if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
				beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
			beanFactory.setConversionService(
					beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
		}


		if (!beanFactory.hasEmbeddedValueResolver()) {
			beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
		}

		String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
		for (String weaverAwareName : weaverAwareNames) {
			getBean(weaverAwareName);
		}

		// Stop using the temporary ClassLoader for type matching.
		beanFactory.setTempClassLoader(null);

		// Allow for caching all bean definition metadata, not expecting further changes.
		beanFactory.freezeConfiguration();

		// 實例化所有非懶加載的單例bean
		beanFactory.preInstantiateSingletons();
}


@Override
public void preInstantiateSingletons() throws BeansException {
		List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

		// 初始化所有非懶加載的單例bean
		for (String beanName : beanNames) {
			RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
			if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
                // 判斷是否是FactoryBean
				if (isFactoryBean(beanName)) {
					Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
					if (bean instanceof FactoryBean) {
						final FactoryBean<?> factory = (FactoryBean<?>) bean;
						boolean isEagerInit;
						if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
							isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>)
											((SmartFactoryBean<?>) factory)::isEagerInit,
									getAccessControlContext());
						}
						else {
							isEagerInit = (factory instanceof SmartFactoryBean &&
									((SmartFactoryBean<?>) factory).isEagerInit());
						}
						if (isEagerInit) {
							getBean(beanName);
						}
					}
				}
				else {
                    // 不是FactoryBean，注意這裏走了獲取Bean的過程
                    // 這裏走getBean/doGetBean的過程，且裏面走了getSingleton(beanName)的過程
                    // 這裏不詳細介紹，總而言之，這裏創建了Bean
					getBean(beanName);
				}
			}
		}

		for (String beanName : beanNames) {
            // 重要，獲取單例bean，這裏使用了三級緩存
			Object singletonInstance = getSingleton(beanName);
			if (singletonInstance instanceof SmartInitializingSingleton) {
				final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
				if (System.getSecurityManager() != null) {
					AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
						smartSingleton.afterSingletonsInstantiated();
						return null;
					}, getAccessControlContext());
				}
				else {
					smartSingleton.afterSingletonsInstantiated();
				}
			}
		}
}

 Object singletonInstance = getSingleton(beanName);這裏是獲取單例Bean，使用了三級緩存，解決Bean的循環依賴也是使用了三級緩存，循環依賴的問題後面再具體看，這裏先看獲取Bean。

DefaultSingletonBeanRegistry中有三個map分別對應三級緩存。

/** Cache of singleton objects: bean name to bean instance.   一級緩存  Bean初始化完成*/
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);

/** Cache of early singleton objects: bean name to bean instance.  二級緩存  Bean未初始化完成*/
private final Map<String, Object> earlySingletonObjects = new HashMap<>(16);

/** Cache of singleton factories: bean name to ObjectFactory.  三級緩存 Bean還未初始化*/
private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<>(16);

再看獲取單例Bean的邏輯

protected Object getSingleton(String beanName, boolean allowEarlyReference) {
       // 先從一級緩存中獲取
		Object singletonObject = this.singletonObjects.get(beanName);
		if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
            // 如果一級緩存存沒有，並且Bean是正在初始化的過程中（還未初始化完成）
			synchronized (this.singletonObjects) {
                // 再從二級緩存中獲取
				singletonObject = this.earlySingletonObjects.get(beanName);
				if (singletonObject == null && allowEarlyReference) {
                    // 如果二級緩存中爲空，allowEarlyReference這裏爲true
                    // 從三級緩存中獲取，注意三級緩存中存放的是ObjectFactory，是創建bean的工廠
					ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
					if (singletonFactory != null) {
                        // 如果ObjectFactory不爲null，創建對象，
                        // 這裏getObject實際是執行的lambada表達式，lambada表達式是創建Bean的邏輯，後面可以再看
						singletonObject = singletonFactory.getObject();
                        // 將創建的Bean放到二級緩存
						this.earlySingletonObjects.put(beanName, singletonObject);
                        // 從三級緩存中刪除，結合上面的put，可以看成是從三級緩存中升級到二級緩存
						this.singletonFactories.remove(beanName);
					}
				}
			}
		}
		return singletonObject;
}

 

十一、結束Refresh

finishRefresh();