Spring IoC容器设计原理（上）

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Spring IoC容器设计原理

对Spring IoC容器，总是能听到几个类似的描述：”Spring IoC原理”，”Spring IoC加载过程”等等，这两个描述都对，容器加载的过程，也就是它的原理。关于Spring IoC，先梳理一下容器体系，主线有两条，一条是以BeanFactory继承体系，一条是以ApplicationContext继承体系。

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BeanFactory作为基本的容器接口，提供了最基本的功能，从方法名可以看出各个方法的功能

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ApplicationContext是高级形态的容器接口，从继承体系看到，ApplicationContext继承了LifeCycle，具备了在容器启动或者关闭时，触发start/stop调用，在AbstractApplicationContext里，会触发各种实现了LifeCycle的start/stop方法的调用。MessageSource跟国际化有关，ApplicationEventPublisher在IoC容器体系中，是一个事件发布器，发布ApplicationEvent事件。

以上的整体体系，大概有个印象即可，接下来，我们从一个简单的测试用例开始，一步步了解IoC容器到底是怎样的，这里还是以最常用的ClassPathXmlApplicationContextTests入手。

容器的加载过程

1、定位Bean的资源文件
2、从资源文件里解析并转为Spring的BeanDefinition，并放入容器
3、初始化Bean，依赖注入

ClassPathXmlApplicationContextTests

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java复制代码@Test
public void testSingleConfigLocation() {
    ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext(FQ_SIMPLE_CONTEXT);
    assertTrue(ctx.containsBean("someMessageSource"));
    ctx.close();
}

这里创建了ClassPathXmlApplicationContext对象，构造器最终是调用

ClassPathXmlApplicationContext

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java复制代码public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)throws BeansException {
	super(parent);
	setConfigLocations(configLocations);
	if (refresh) {
            refresh();
	}
}

refresh是IoC容器启动的核心方法

AbstractApplicationContext

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java复制代码
public void refresh() throws BeansException, IllegalStateException {
	synchronized (this.startupShutdownMonitor) {
		// 准备容器环境，如设置启动时间，激活flag状态
		prepareRefresh();

		// 由子类refresh容器
		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.
			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();
		}
	}
}

obtainFreshBeanFactory方法

AbstractApplicationContext

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java复制代码protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
	refreshBeanFactory();
	ConfigurableListableBeanFactory beanFactory = getBeanFactory();
	if (logger.isDebugEnabled()) {
		logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
	}
	return beanFactory;
}

refreshBeanFactory()和getBeanFactory()都是抽象方法，留给子类实现

AbstractRefreshableApplicationContext

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java复制代码protected final void refreshBeanFactory() throws BeansException {
	// 如果容器已存在，就销毁
        if (hasBeanFactory()) {
		destroyBeans();
		closeBeanFactory();
	}
	try {
		DefaultListableBeanFactory beanFactory = createBeanFactory();
		beanFactory.setSerializationId(getId());
		customizeBeanFactory(beanFactory);
                // 加载Bean的入口，里面的调用栈很深，比较容易迷失自我
		loadBeanDefinitions(beanFactory);
		synchronized (this.beanFactoryMonitor) {
			this.beanFactory = beanFactory;
		}
	}
	catch (IOException ex) {
		throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
	}
}

refreshBeanFactory()首先是判断容器是否存在，存在就销毁，然后重新创建一个DefaultListableBeanFactory，接下来的核心是loadBeanDefinitions(beanFactory)

loadBeanDefinitions()方法

AbstractRefreshableApplicationContext

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java复制代码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));

	// beanDefinitionReader可以由子类实现，比如我们使用xml定义Bean，使用的是XmlBeanDefinitionReader
	initBeanDefinitionReader(beanDefinitionReader);
	loadBeanDefinitions(beanDefinitionReader);
}

从一开始的setConfigLocations，已经定位到Bean的资源文件，而这里，就是要加载并解析Bean定义，解析的过程实质是委托给XmlBeanDefinitionReader

XmlBeanDefinitionReader

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java复制代码protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
			throws BeanDefinitionStoreException {
	try {
		Document doc = doLoadDocument(inputSource, resource);
		return registerBeanDefinitions(doc, resource);
	}
	...
}

真正把xml解析成BeanDefinition是在registerBeanDefinition方法

XmlBeanDefinitionReader

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java复制代码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;
}

在这个方法里，documentReader.registerBeanDefinitions(doc, createReaderContext(resource)) 进行解析，具体的解析工作，是委托给BeanDefinitionParserDelegate类完成的

在这里要注意，XmlBeanDefinitionReader是持有BeanFactory对象的，createReaderContext(resource)方法里，把XmlBeanDefinitionReader的this传递给了XmlReaderContext(createReaderContext的返回对象），也就是说，XmlReaderContext间接持有BeanFactory对象

DefaultBeanDefinitionDocumentReader

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

DefaultBeanDefinitionDocumentReader

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java复制代码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);
			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;
			}
		}
	}

	preProcessXml(root);
        // 委托BeanDefinitionParserDelegate解析
	parseBeanDefinitions(root, this.delegate);
	postProcessXml(root);

	this.delegate = parent;
}

从这个方法可以知道，真正解析的确实是BeanDefinitionParserDelegate，而BeanDefinitionParserDelegate也是间接持有BeanFactory对象。继续进入parseBeanDefinitions(root, this.delegate)，会进入到

AbstractBeanDefinitionParser

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java复制代码public final BeanDefinition parse(Element element, ParserContext parserContext) {
	AbstractBeanDefinition definition = parseInternal(element, parserContext);
	if (definition != null && !parserContext.isNested()) {
		try {
			String id = resolveId(element, definition, parserContext);
			if (!StringUtils.hasText(id)) {
				parserContext.getReaderContext().error(
						"Id is required for element '" + parserContext.getDelegate().getLocalName(element)
								+ "' when used as a top-level tag", element);
			}
			String[] aliases = null;
			if (shouldParseNameAsAliases()) {
				String name = element.getAttribute(NAME_ATTRIBUTE);
				if (StringUtils.hasLength(name)) {
					aliases = StringUtils.trimArrayElements(StringUtils.commaDelimitedListToStringArray(name));
				}
			}
                        // BeanDefinition封装成BeanDefinitionHolder
			BeanDefinitionHolder holder = new BeanDefinitionHolder(definition, id, aliases);
                        // 注册BeanDefinitionHolder
			registerBeanDefinition(holder, parserContext.getRegistry());
			if (shouldFireEvents()) {
				BeanComponentDefinition componentDefinition = new BeanComponentDefinition(holder);
				postProcessComponentDefinition(componentDefinition);
				parserContext.registerComponent(componentDefinition);
			}
		}
		catch (BeanDefinitionStoreException ex) {
			String msg = ex.getMessage();
			parserContext.getReaderContext().error((msg != null ? msg : ex.toString()), element);
			return null;
		}
	}
	return definition;
}

这里再说明一下，ParserContext也是间接持有BeanFactory对象，而直接持有的是XmlReaderContext对象。BeanDefinition已经解析出来，并且再次封装为BeanDefinitionHolder，接下来就该是放入到容器里了，逻辑在registerBeanDefinition(holder, parserContext.getRegistry());进去后，会进入到BeanDefinitionReaderUtils

BeanDefinitionReaderUtils

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java复制代码public static void registerBeanDefinition(
		BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
		throws BeanDefinitionStoreException {

	// Register bean definition under primary name.
	String beanName = definitionHolder.getBeanName();
	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);
		}
	}
}

再走进registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition())，这个方法有点长，省去了前面部分

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java复制代码public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
			throws BeanDefinitionStoreException {

	// 省略...
        
	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);
	if (existingDefinition != null) {
		
		// ...
		// 如果已存在，直接覆盖
		this.beanDefinitionMap.put(beanName, beanDefinition);
	}
	else {
		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
			this.beanDefinitionMap.put(beanName, beanDefinition);
			this.beanDefinitionNames.add(beanName);
			this.manualSingletonNames.remove(beanName);
		}
		this.frozenBeanDefinitionNames = null;
	}

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

结果一目了然，this.beanDefinitionMap.put(beanName, beanDefinition); 所以说，Spring IoC容器本质就是个HashMap。解析工作到这，基本ok了，但是放入容器的beanDefinition，解决了依赖的问题了吗？没有。

到这里，我们已经进入到很深的层级了，所以要退回去，退回到AbstractApplicationContext的obtainFreshBeanFactory()，其实这个方法也基本结束了，直接返回beanFactory，所以我们还得回到refresh()，再贴一下代码

prepareBeanFactory方法

AbstractApplicationContext

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java复制代码public void refresh() throws BeansException, IllegalStateException {
	synchronized (this.startupShutdownMonitor) {
		// 准备容器环境，如设置启动时间，激活flag状态
		prepareRefresh();

		// 由子类refresh容器
		ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

		// 准备容器的一些特性，比如ClassLoader、post-processors
		prepareBeanFactory(beanFactory);

		try {
			// 空实现，由子类注册callback
			postProcessBeanFactory(beanFactory);

			// 执行eBeanFactoryPostProcessor的方法
			invokeBeanFactoryPostProcessors(beanFactory);

			// 注册BeanPostProcessors
			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();
		}
	}
}

prepareBeanFactory方法，先看一下代码

AbstractApplicationContext

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java复制代码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());
		}
	}

这里比较感兴趣的是注册的Aware类，Aware类是Spring提供的一种回调机制，比较常用的如ApplicationContextAware，这里实质是放在一个HashSet里。Aware本身是一个没有定义方法的接口，ApplicationContextAware只有一个setApplicationContext方法，ApplicationEventPublisherAware只有一个setApplicationEventPublisher方法，那么这些Aware方法，是在哪里调用呢？

查一下测试demo：org.springframework.context.support.StaticApplicationContextTests#count，另一个类是org.springframework.context.ACATester#setApplicationContext，断点setApplicationContext，启动count

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看调用链得知，是在实例化Bean的时候调用的，实例化过程，后面会继续讲，从调用链来看，有意思的是ApplicationContextAwareProcessor类，这是个BeanPostProcessor，是在Bean实例化时做扩展的，很多场景都有用到，BeanPostProcessor提供了两个方法postProcessBeforeInitialization和postProcessAfterInitialization，所以得知，Aware的那些方法，是在BeanPostProcessor触发调用的

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java复制代码private void invokeAwareInterfaces(Object bean) {
	if (bean instanceof Aware) {
		if (bean instanceof EnvironmentAware) {
			((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
		}
		if (bean instanceof EmbeddedValueResolverAware) {
			((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
		}
		if (bean instanceof ResourceLoaderAware) {
			((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
		}
		if (bean instanceof ApplicationEventPublisherAware) {
			((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
		}
		if (bean instanceof MessageSourceAware) {
			((MessageSourceAware) bean).setMessageSource(this.applicationContext);
		}
		if (bean instanceof ApplicationContextAware) {
			((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
		}
	}
}

postProcessBeanFactory方法是抽象方法，由子类实现，如AbstractRefreshableWebApplicationContext，把servletContext和servletConfig封装成BeanPostProcessor，注册到容器中

invokeBeanFactoryPostProcessors方法

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java复制代码protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
	PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

	// Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
	// (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
	if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
		beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
		beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
	}
}

invokeBeanFactoryPostProcessors主要是执行之前注册的BeanFactoryPostProcessor，BeanFactoryPostProcessor和BeanPostProcessor一样，都是Spring的扩展点，单二者的使用场景不同，BeanFactoryPostProcessor提供了一个方法postProcessBeanFactory，在容器的BeanFactory初始化之后（指BeanDefinition已经加载进容器了，但是还没实例化），可以通过这个方法去对早期暴露的Bean覆盖或者增加Bean的一些配置

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java复制代码public interface BeanFactoryPostProcessor {

	/**
	 * Modify the application context's internal bean factory after its standard
	 * initialization. All bean definitions will have been loaded, but no beans
	 * will have been instantiated yet. This allows for overriding or adding
	 * properties even to eager-initializing beans.
	 * @param beanFactory the bean factory used by the application context
	 * @throws org.springframework.beans.BeansException in case of errors
	 */
	void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;

}

一个典型的例子是ConfigurationClassPostProcessor，该接口继承BeanFactoryPostProcessor，用来对Configure配置类做增强

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java复制代码/**
 * Prepare the Configuration classes for servicing bean requests at runtime
 * by replacing them with CGLIB-enhanced subclasses.
 */
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
	int factoryId = System.identityHashCode(beanFactory);
	if (this.factoriesPostProcessed.contains(factoryId)) {
		throw new IllegalStateException(
				"postProcessBeanFactory already called on this post-processor against " + beanFactory);
	}
	this.factoriesPostProcessed.add(factoryId);
	if (!this.registriesPostProcessed.contains(factoryId)) {
		// BeanDefinitionRegistryPostProcessor hook apparently not supported...
		// Simply call processConfigurationClasses lazily at this point then.
		processConfigBeanDefinitions((BeanDefinitionRegistry) beanFactory);
	}

	enhanceConfigurationClasses(beanFactory);
	beanFactory.addBeanPostProcessor(new ImportAwareBeanPostProcessor(beanFactory));
}

registerBeanPostProcessors方法

registerBeanPostProcessors方法注册BeanPostProcessor，在Bean实例化是调用其方法，该方法委托PostProcessorRegistrationDelegate的registerBeanPostProcessors实例化和注册BeanPostProcessor，

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java复制代码public static void registerBeanPostProcessors(
			ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

	String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

	// Register BeanPostProcessorChecker that logs an info message when
	// a bean is created during BeanPostProcessor instantiation, i.e. when
	// a bean is not eligible for getting processed by all BeanPostProcessors.
	int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
	beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

	// Separate between BeanPostProcessors that implement PriorityOrdered,
	// Ordered, and the rest.
	List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
	List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
	List<String> orderedPostProcessorNames = new ArrayList<>();
	List<String> nonOrderedPostProcessorNames = new ArrayList<>();
	for (String ppName : postProcessorNames) {
		if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
			BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
			priorityOrderedPostProcessors.add(pp);
			if (pp instanceof MergedBeanDefinitionPostProcessor) {
				internalPostProcessors.add(pp);
			}
		}
		else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
			orderedPostProcessorNames.add(ppName);
		}
		else {
			nonOrderedPostProcessorNames.add(ppName);
		}
	}

	// First, register the BeanPostProcessors that implement PriorityOrdered.
	sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
	registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

	// Next, register the BeanPostProcessors that implement Ordered.
	List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();
	for (String ppName : orderedPostProcessorNames) {
		BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
		orderedPostProcessors.add(pp);
		if (pp instanceof MergedBeanDefinitionPostProcessor) {
			internalPostProcessors.add(pp);
		}
	}
	sortPostProcessors(orderedPostProcessors, beanFactory);
	registerBeanPostProcessors(beanFactory, orderedPostProcessors);

	// Now, register all regular BeanPostProcessors.
	List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
	for (String ppName : nonOrderedPostProcessorNames) {
		BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
		nonOrderedPostProcessors.add(pp);
		if (pp instanceof MergedBeanDefinitionPostProcessor) {
			internalPostProcessors.add(pp);
		}
	}
	registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

	// Finally, re-register all internal BeanPostProcessors.
	sortPostProcessors(internalPostProcessors, beanFactory);
	registerBeanPostProcessors(beanFactory, internalPostProcessors);

	// Re-register post-processor for detecting inner beans as ApplicationListeners,
	// moving it to the end of the processor chain (for picking up proxies etc).
	beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}

这个方法的逻辑挺简单，主要是把BeanPostProcessor根据PriorityOrdered和Ordered排序，并添加到BeanFactory里，最后是把没有排序的也添加到BeanFactory

到此，需要说明一下，BeanDefinition已经注册到容器里了，但是还没进行实例化，也没有进行依赖注入，BeanPostProcessor也注册到容器了。

看到这，可以发现AbstractApplicationContext继承体系，就是典型的模板方法的使用案例

本文转载自: 掘金

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