（五）SpringBoot啟動過程的分析-刷新ApplicationContext

-- 以下內容均基於2.1.8.RELEASE版本

緊接着上一篇（四）SpringBoot啟動過程的分析-預處理ApplicationContext, 本文將分析上下文容器准備完成之后開始執行刷新流程

// SpringApplication.java

private void refreshContext(ConfigurableApplicationContext context) {
	refresh(context);
	if (this.registerShutdownHook) {
		try {
			context.registerShutdownHook();
		}
		catch (AccessControlException ex) {
			// Not allowed in some environments.
		}
	}
}

// 真正的refresh方法在AbstractApplicationContext類中
protected void refresh(ApplicationContext applicationContext) {
	Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
	((AbstractApplicationContext) applicationContext).refresh();
}

// AbstractApplicationContext.java
public void refresh() throws BeansException, IllegalStateException {
	synchronized (this.startupShutdownMonitor) {
		// Prepare this context for refreshing.
		prepareRefresh();

		// Tell the subclass to refresh the internal 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.
			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();
		}
	}
}

在refresh方法中清晰的划分了刷新容器的步驟。

prepareRefresh()

主要用於清除元數據Reader的緩存，設置應用程序啟動的時間，設置應用程序的活動標記，初始化屬性源。

// AnnotationConfigServletWebServerApplicationContext.java

protected void prepareRefresh() {
	this.scanner.clearCache();
	super.prepareRefresh();
}

// AbstractApplicationContext.java

protected void prepareRefresh() {
	// 設置開始執行的時間和活動標記
	this.startupDate = System.currentTimeMillis();
	this.closed.set(false);
	this.active.set(true);

	if (logger.isDebugEnabled()) {
		if (logger.isTraceEnabled()) {
			logger.trace("Refreshing " + this);
		}
		else {
			logger.debug("Refreshing " + getDisplayName());
		}
	}

	// ①
	initPropertySources();

	// ②
	// Validate that all properties marked as required are resolvable:
	// see ConfigurablePropertyResolver#setRequiredProperties
	getEnvironment().validateRequiredProperties();

	// ③
	// Store pre-refresh ApplicationListeners...
	if (this.earlyApplicationListeners == null) {
		this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
	}
	else {
		// Reset local application listeners to pre-refresh state.
		this.applicationListeners.clear();
		this.applicationListeners.addAll(this.earlyApplicationListeners);
	}

	// Allow for the collection of early ApplicationEvents,
	// to be published once the multicaster is available...
	this.earlyApplicationEvents = new LinkedHashSet<>();
}

① - 初始化屬性資源

// StandardServletEnvironment.java

public void initPropertySources(@Nullable ServletContext servletContext, @Nullable ServletConfig servletConfig) {
	WebApplicationContextUtils.initServletPropertySources(getPropertySources(), servletContext, servletConfig);
}

// WebApplicationContextUtils.java

public static void initServletPropertySources(MutablePropertySources sources,
		@Nullable ServletContext servletContext, @Nullable ServletConfig servletConfig) {

	Assert.notNull(sources, "'propertySources' must not be null");
	String name = StandardServletEnvironment.SERVLET_CONTEXT_PROPERTY_SOURCE_NAME;
	// servletContext不為空且有相關配置的情況
	if (servletContext != null && sources.contains(name) && sources.get(name) instanceof StubPropertySource) {
		sources.replace(name, new ServletContextPropertySource(name, servletContext));
	}
	// servletConfig不為空且有相關配置的情況
	name = StandardServletEnvironment.SERVLET_CONFIG_PROPERTY_SOURCE_NAME;
	if (servletConfig != null && sources.contains(name) && sources.get(name) instanceof StubPropertySource) {
		sources.replace(name, new ServletConfigPropertySource(name, servletConfig));
	}
}

在內部調用了WebApplicationContextUtils.initServletPropertySources方法，由名稱可得知，它用於初始化Servlet的屬性資源，在實際執行過程中分別根據ServletContext和ServletConfig的值來判定是否要將指定的配置包裝為ServletContextPropertySource、ServletConfigPropertySource在實際調試過程中他們的值都為空，也就是沒有進行任何操作。

② - 檢查必備屬性，此處是用於檢查哪些屬性是必不可少的，例如可以設置"example.address"這個屬性必須不為空。
③ - 重新對監聽器排序

prepareBeanFactory(beanFactory)

// AbstractApplicationContext.java

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
	
	// 設置類加載器
	// Tell the internal bean factory to use the context's class loader etc.
	beanFactory.setBeanClassLoader(getClassLoader());
	// 設置SpringEL表達式解析器
	beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
	// 設置屬性編輯器注冊
	beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

	// ① 忽略指定的接口注入
	// 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);

	// 指定對特定接口注入時實際的注入對象，例如有某對象想要注入BeanFactory，則實際將會指定它注入的是當前設置的BeanFactory
	// 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);

	// 添加和移除ApplicationListener
	// 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()));
	}

	// 注冊默認環境對象
	// Register default environment beans.
	if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
		beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
	}
	
	// 注冊系統配置對象
	if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
		beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
	}
	
	// 注冊系統環境對象
	if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
		beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
	}
}

① - 這里的忽略依賴接口，是指這些Aware接口的實現類在Spring中將會自動忽略接口實現類中和setter方法入參相同的類型，舉例說明

public interface EnvironmentAware extends Aware {
	void setEnvironment(Environment environment);
}

public class MyEnvironmentAware implements Environment {

	private Environment environment;
	
	@Overwired
	public void setEnvironment(Environment environment) {
		this.environment = environment;
	}

}

示例中展示了如何使用EnvironmentAware接口來實現在自定義代碼中獲取Environment，上面所說的忽略，是指在Spring自動裝配MyEnvironment這個類的時候，會自動忽略到setEnvironment方法中的Environment對象注入。在忽略接口的第一行代碼添加了一個ApplicationContextAwareProcessor，而它則是Spring框架統一來設置這些Aware接口實現類的處理器。

postProcessBeanFactory(beanFactory)

在當前AbstractApplicationContext類中的postProcessBeanFactory方法並未實現，由其子類實現。

// AnnotationConfigServletWebServerApplicationContext.java
// 實現一
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
	// ①
	super.postProcessBeanFactory(beanFactory);
	// ②
	if (this.basePackages != null && this.basePackages.length > 0) {
		this.scanner.scan(this.basePackages);
	}
	// ③
	if (!this.annotatedClasses.isEmpty()) {
		this.reader.register(ClassUtils.toClassArray(this.annotatedClasses));
	}
}

① - 調用父類的實現

// ServletWebServerApplicationContext.java

protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
	// 添加用於處理WebApplicationContextServletContextAware接口的processor
	beanFactory.addBeanPostProcessor(new WebApplicationContextServletContextAwareProcessor(this));
	// 忽略ServletContextAware接口的注入
	beanFactory.ignoreDependencyInterface(ServletContextAware.class);
	registerWebApplicationScopes();
}

// 注冊web應用的作用域
public static void registerWebApplicationScopes(ConfigurableListableBeanFactory beanFactory,
		@Nullable ServletContext sc) {

	beanFactory.registerScope(WebApplicationContext.SCOPE_REQUEST, new RequestScope());
	beanFactory.registerScope(WebApplicationContext.SCOPE_SESSION, new SessionScope());
	if (sc != null) {
		ServletContextScope appScope = new ServletContextScope(sc);
		beanFactory.registerScope(WebApplicationContext.SCOPE_APPLICATION, appScope);
		// Register as ServletContext attribute, for ContextCleanupListener to detect it.
		sc.setAttribute(ServletContextScope.class.getName(), appScope);
	}

	beanFactory.registerResolvableDependency(ServletRequest.class, new RequestObjectFactory());
	beanFactory.registerResolvableDependency(ServletResponse.class, new ResponseObjectFactory());
	beanFactory.registerResolvableDependency(HttpSession.class, new SessionObjectFactory());
	beanFactory.registerResolvableDependency(WebRequest.class, new WebRequestObjectFactory());
	if (jsfPresent) {
		FacesDependencyRegistrar.registerFacesDependencies(beanFactory);
	}
}

② - 根據basePackage指定的位置進行掃描bean
③ - 根據注解來掃描指定的bean

invokeBeanFactoryPostProcessors()

主要用於調用BeanFactoryPostProcessors的實現

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
	// 調用BeanFactoryPostProcessor
	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()));
	}
}

在調用BeanFactoryPostProcessor時，會首先調用BeanDefinitionRegistryPostProcessor, 因為后者是對前者的擴展，並且有可能在后者中又重新注冊了前者的其他實例。由於PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors（）方法過長，這里直接寫行內注釋能夠比較直觀的分析前后關系。

public static void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {

	// Invoke BeanDefinitionRegistryPostProcessors first, if any.
	// 已處理的Bean
	Set<String> processedBeans = new HashSet<>();

	// 判斷當前的BeanFactory是否為一個Bean注冊器，實際上就是代表同時實現了BeanDefinitionRegistryPostProcessor和BeanFactoryPostProcessor接口的實現
	// 對於同時實現兩個接口的類，將先調用BeanDefinitionRegistryPostProcessor里面的方法，再調用BeanFactoryPostProcessor里面的方法
	// 在調用的時候又要區分是實現了PriorityOrdered還是Ordered接口。
	if (beanFactory instanceof BeanDefinitionRegistry) {
	
		// 轉換為注冊器
		BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
		// 用於存放常規的BeanFactoryPostProcessor
		List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
		// 用於存放BeanFactoryPostProcessor的擴展BeanDefinitionRegistryPostProcessor，這里是一個匯總的列表
		List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();

		// 遍歷傳入的BeanFactoryPostProcessor
		for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
			// 優先執行BeanFactoryPostProcessor的擴展類BeanDefinitionRegistryPostProcessor，它的優先級最高
			if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
				// 類型轉換
				BeanDefinitionRegistryPostProcessor registryProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor;
				// 調用postProcessBeanDefinitionRegistry()方法，內部可能注冊了Bean，也可能重新定義了一些普通的BeanFactoryPostProcessor
				registryProcessor.postProcessBeanDefinitionRegistry(registry);
				// 添加到已處理列表
				registryProcessors.add(registryProcessor);
			}
			else {
				//	對比上面if代碼塊會發現，這里沒有作調用，直接先保存在常規列表內部，因為常規的Processor在調用的時候還有其他考慮，接着往下看便是
				regularPostProcessors.add(postProcessor);
			}
		}

		// 不要在這里初始化FactoryBean（請看清是FactoryBean，工廠類，不是類工廠（BeanFactory），他們有巨大的差異），需要保留所有的常規類未初始化，以便使用BeanFactoryPostProcessor對其處理
		// Do not initialize FactoryBeans here: We need to leave all regular beans
		// uninitialized to let the bean factory post-processors apply to them!
		
		// 根據BeanDefinitionRegistryPostProcessors 實現的接口划分為三類：實現了PriorityOrdered的、實現了Ordered的以及前面兩者都沒實現的
		// Separate between BeanDefinitionRegistryPostProcessors that implement
		// PriorityOrdered, Ordered, and the rest.
		
		// 保存當前將要處理的BeanDefinitionRegistryPostProcessor列表，每處理完一種分類的就清空
		List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

		// 首先調用實現了PriorityOrdered接口的BeanDefinitionRegistryPostProcessors
		// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
		
		// 獲取當前Bean工廠內部所有的，類型為BeanDefinitionRegistryPostProcessor.class的后處理器名稱
		String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
		
		for (String ppName : postProcessorNames) {
			if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
				// 篩選出實現了PriorityOrdered接口的后處理器，放入當前處理列表
				currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
				// 同時放入已處理列表
				processedBeans.add(ppName);
			}
		}
		
		// 按照優先級排序
		sortPostProcessors(currentRegistryProcessors, beanFactory);
		// 添加實現了PriorityOrder接口的BeanDefinitionRegistryPostProcessor到它的匯總列表里面
		registryProcessors.addAll(currentRegistryProcessors);
		// 調用所有的BeanDefinitionRegistryPostProcessor實例的postProcessBeanDefinitionRegistry()方法
		invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
		// 清除內部的實現了PriorityOrder的BeanDefinitionRegistryPostProcessor
		currentRegistryProcessors.clear();

		// 上面是處理實現了PriorityOrdered接口的，這里處理實現了Ordered接口的, 為何這里又獲取了一次postProcessorNames，前面不是才獲取么？
		// 這里獲取一次是因為前面處理的時候有可能又加入了新的BeanDefinitionRegistryPostProcessor
		// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
		postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
		for (String ppName : postProcessorNames) {
			if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
				currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
				processedBeans.add(ppName);
			}
		}
		sortPostProcessors(currentRegistryProcessors, beanFactory);
		registryProcessors.addAll(currentRegistryProcessors);
		invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
		// 清空上一步已經執行過的
		currentRegistryProcessors.clear();

		// 繼續調用普通的BeanDefinitionRegistryPostProcessors
		// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
		boolean reiterate = true;
		while (reiterate) {
			reiterate = false;
			postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
			for (String ppName : postProcessorNames) {
				if (!processedBeans.contains(ppName)) {
					currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
					processedBeans.add(ppName);
					reiterate = true;
				}
			}
			sortPostProcessors(currentRegistryProcessors, beanFactory);
			registryProcessors.addAll(currentRegistryProcessors);
			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
			currentRegistryProcessors.clear();
		}

		// 最后調用普通的 BeanFactoryPostProcessor，
		// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
		invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
		
		//因為BeanDefinitionRegistryPostProcessor也是繼承了BeanFactoryPostProcessor，，也具有postProcessBeanFactory（）方法的，所以也需要執行
		invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
	}

	else {
		// 若不是BeanDefinitionRegistry，那就是直接實現了BeanFactoryPostProcessor
		// Invoke factory processors registered with the context instance.
		invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
	}

	// 下面這部分邏輯就和上面套路一樣，無非處理的是BeanFactoryPostProcessor罷了
	// Do not initialize FactoryBeans here: We need to leave all regular beans
	// uninitialized to let the bean factory post-processors apply to them!
	String[] postProcessorNames =
			beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

	// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
	// Ordered, and the rest.
	List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
	List<String> orderedPostProcessorNames = new ArrayList<>();
	List<String> nonOrderedPostProcessorNames = new ArrayList<>();
	for (String ppName : postProcessorNames) {
		if (processedBeans.contains(ppName)) {
			// skip - already processed in first phase above
		}
		else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
			priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
		}
		else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
			orderedPostProcessorNames.add(ppName);
		}
		else {
			nonOrderedPostProcessorNames.add(ppName);
		}
	}

	// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
	sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
	invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

	// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
	List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>();
	for (String postProcessorName : orderedPostProcessorNames) {
		orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
	}
	sortPostProcessors(orderedPostProcessors, beanFactory);
	invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

	// Finally, invoke all other BeanFactoryPostProcessors.
	List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
	for (String postProcessorName : nonOrderedPostProcessorNames) {
		nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
	}
	invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

	// Clear cached merged bean definitions since the post-processors might have
	// modified the original metadata, e.g. replacing placeholders in values...
	beanFactory.clearMetadataCache();
}

小結

BeanFactoryPostProcessors是Spring框架中的一個很重要的擴展入口，通過它可以在Bean實例化之前進行一些修改，從類型上分為BeanDefinitionRegistryPostProcessor和BeanFactoryPostProcessor，在內部處理過程中，前者的優先級高於后者。與此同時，他們分別還會按照PriorityOrdered > Ordered > 默認
的優先級順序來進行處理。了解他們執行順序這點很重要，后續如有擴展需求就可以精准植入自己的邏輯。需要注意的是，這些處理器本身就是用於注冊Bean，因此他們也可以注冊和自己類型一樣的擴展類。在使用的時候尤其要注意這點。例如在實現了PriorityOrdered的BeanDefinitionRegistryPostProcessor中
再注冊一個實現了Ordered的BeanDefinitionRegistryPostProcessor，雖然這樣沒問題，但筆者認為這樣代碼隱藏過深。不利於后期維護。建議使用SPI機制來配置，簡潔明了。

registerBeanPostProcessors()

主要用於調用BeanPostProcessors的實現，區別於上一個章節，本章節處理的是實例化過后的Bean。

// AbstractApplicationContext.java

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
	// 調用BeanPostProcessor
	PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
}


// PostProcessorRegistrationDelegate.java

public static void registerBeanPostProcessors(
		ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

	// 獲取所有的BeanPostProcessor名稱
	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.
	
	// 注冊一個BeanPostProcessorChecker，當一個BeanPostProcessor在實例化期間創建一個Bean的時候，打印日志
	int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
	beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

	// 按照優先級整理
	
	// 實現了PriorityOrdered接口的BeanPostProcessor集合
	List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
	// 內部定義的BeanPostProcessor集合
	List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
	// 實現了Ordered接口的BeanPostProcessor名稱集合
	List<String> orderedPostProcessorNames = new ArrayList<>();
	// 未實現排序優先級接口的BeanPostProcessor名稱集合
	List<String> nonOrderedPostProcessorNames = new ArrayList<>();
	
	// 分別放入不同集合內
	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);
		}
	}

	// 注冊實現了PriorityOrdered接口的BeanPostProcessor
	// First, register the BeanPostProcessors that implement PriorityOrdered.
	sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
	registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

	// 注冊實現了PriorityOrdered接口的BeanPostProcessor
	// 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);

	// 注冊常規的BeanPostProcessor
	// 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);

	// 重新注冊所有的內部BeanPostProcessor
	// Finally, re-register all internal BeanPostProcessors.
	sortPostProcessors(internalPostProcessors, beanFactory);
	registerBeanPostProcessors(beanFactory, internalPostProcessors);

	// 注冊ApplicationListenerDetector，它將在bean初始化完成之后檢測是否為ApplicationListener，如果是則加入applicationListeners中
	// 在Bean銷毀之前，提前從ApplicationEventMulticaster中刪除
	// 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));
}

initMessageSource()

初始化MessageSource，若當前上下文中未定義，則使用父類中的定義

// AbstractApplicationContext.java

protected void initMessageSource() {
	ConfigurableListableBeanFactory beanFactory = getBeanFactory();
	if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
		this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
		// Make MessageSource aware of parent MessageSource.
		if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
			HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
			if (hms.getParentMessageSource() == null) {
				// Only set parent context as parent MessageSource if no parent MessageSource
				// registered already.
				hms.setParentMessageSource(getInternalParentMessageSource());
			}
		}
		if (logger.isTraceEnabled()) {
			logger.trace("Using MessageSource [" + this.messageSource + "]");
		}
	}
	else {
		// Use empty MessageSource to be able to accept getMessage calls.
		DelegatingMessageSource dms = new DelegatingMessageSource();
		dms.setParentMessageSource(getInternalParentMessageSource());
		this.messageSource = dms;
		beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
		if (logger.isTraceEnabled()) {
			logger.trace("No '" + MESSAGE_SOURCE_BEAN_NAME + "' bean, using [" + this.messageSource + "]");
		}
	}
}

initApplicationEventMulticaster()

主要用於設置事件發布器，若當前上下文沒有定義ApplicationEventMulticaster 則使用 SimpleApplicationEventMulticaster

// AbstractApplicationContext.java

protected void initApplicationEventMulticaster() {
	ConfigurableListableBeanFactory beanFactory = getBeanFactory();
	if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
		this.applicationEventMulticaster =
				beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
		if (logger.isTraceEnabled()) {
			logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
		}
	}
	else {
		this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
		beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
		if (logger.isTraceEnabled()) {
			logger.trace("No '" + APPLICATION_EVENT_MULTICASTER_BEAN_NAME + "' bean, using " +
					"[" + this.applicationEventMulticaster.getClass().getSimpleName() + "]");
		}
	}
}

onRefresh()

當前類中沒有實現，只是作為一個模板，將由子類來實現

// AbstractApplicationContext.java

protected void onRefresh() throws BeansException {
	// For subclasses: do nothing by default.
}

// ServletWebServerApplicationContext.java
protected void onRefresh() {
	// 父類中僅僅設置了一下主題，無關緊要
	super.onRefresh();
	try {
		// 創建Web服務器
		createWebServer();
	}
	catch (Throwable ex) {
		throw new ApplicationContextException("Unable to start web server", ex);
	}
}

創建Web服務器

這里只簡單介紹一下它啟動了內置的Web容器，Web容器的初始化后續會有單獨篇章分析。

private void createWebServer() {
	// ①
	WebServer webServer = this.webServer;
	// ②
	ServletContext servletContext = getServletContext();
	// ③
	if (webServer == null && servletContext == null) {
		ServletWebServerFactory factory = getWebServerFactory();
		this.webServer = factory.getWebServer(getSelfInitializer());
	}
	// ④
	else if (servletContext != null) {
		try {
			getSelfInitializer().onStartup(servletContext);
		}
		catch (ServletException ex) {
			throw new ApplicationContextException("Cannot initialize servlet context", ex);
		}
	}
	// ⑤
	initPropertySources();
}

① - 當前應用的WEB服務器，也就是Servlet容器。
② - 當前應用的上下文，一個應用使用一個ServletContext來表示。
③ - 使用ServletWebServerFactory創建一個Servlet容器
④ - 手動配置上下文的接口。
⑤ - 初始化配置信息，實際上就是將環境信息中的'servletContextInitParams':StubPropertySource 轉換為'servletContextInitParams': ServletContextPropertySource; 將 'servletConfigInitParams': StubPropertySource轉換為'servletConfigInitParams':ServletConfigPropertySource

registerListeners()

主要用於將獲取到的所有監聽器委托給applicationEventMulticaster。

protected void registerListeners() {
	
	// ① 
	// Register statically specified listeners first.
	for (ApplicationListener<?> listener : getApplicationListeners()) {
		getApplicationEventMulticaster().addApplicationListener(listener);
	}

	// ②
	// Do not initialize FactoryBeans here: We need to leave all regular beans
	// uninitialized to let post-processors apply to them!
	String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
	for (String listenerBeanName : listenerBeanNames) {
		getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
	}

	// ③
	// Publish early application events now that we finally have a multicaster...
	Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
	this.earlyApplicationEvents = null;
	if (earlyEventsToProcess != null) {
		for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
			getApplicationEventMulticaster().multicastEvent(earlyEvent);
		}
	}
}

① - 將內部注冊的監聽器委托給廣播器applicationEventMulticaster。
② - 檢測BeanFactory內部的監聽器
③ - 發布早期事件

finishBeanFactoryInitialization()

實例化剩下的所有單例Bean（非延遲加載的）

// AbstractApplicationContext.java

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
	
	// ①
	// Initialize conversion service for this context.
	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));
	}

	// ②
	// Register a default embedded value resolver if no bean post-processor
	// (such as a PropertyPlaceholderConfigurer bean) registered any before:
	// at this point, primarily for resolution in annotation attribute values.
	if (!beanFactory.hasEmbeddedValueResolver()) {
		beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
	}

	// ③
	// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
	String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
	for (String weaverAwareName : weaverAwareNames) {
		getBean(weaverAwareName);
	}

	// ④
	// Stop using the temporary ClassLoader for type matching.
	beanFactory.setTempClassLoader(null);

	// ⑤
	// Allow for caching all bean definition metadata, not expecting further changes.
	beanFactory.freezeConfiguration();

	// ⑤
	// Instantiate all remaining (non-lazy-init) singletons.
	beanFactory.preInstantiateSingletons();
}

① - 判斷是否有轉換服務
② - 判斷是否有占位符解析器
③ - 注冊LoadTimeWeaverAware
④ - 停止使用臨時的ClassLoader進行類型匹配，實際上它就是空值
⑤ - 凍結所有的BeanDefinition，通過configurationFrozen = true 和 frozenBeanDefinitionNames（包含所有的BeanDefinition）配合鎖定
⑥ - 實例化剩下的所有單例Bean（非延遲加載的），其實就是從注冊器緩存里面取出（DefaultSingletonBeanRegistry）

finishRefresh()

// ServletWebServerApplicationContext.java
@Override
protected void finishRefresh() {
	// 父類執行finishRefresh
	super.finishRefresh();
	// 啟動web容器
	WebServer webServer = startWebServer();
	if (webServer != null) {
		// 發布web容器啟動完成事件
		publishEvent(new ServletWebServerInitializedEvent(webServer, this));
	}
}

// AbstractApplicationContext.java

protected void finishRefresh() {
	
	// ① Clear context-level resource caches (such as ASM metadata from scanning).
	clearResourceCaches();

	// ② Initialize lifecycle processor for this context.
	initLifecycleProcessor();

	// ③ Propagate refresh to lifecycle processor first.
	getLifecycleProcessor().onRefresh();

	// ④ Publish the final event.
	publishEvent(new ContextRefreshedEvent(this));

	// ⑤ Participate in LiveBeansView MBean, if active.
	LiveBeansView.registerApplicationContext(this);
}

① - 清除資源緩存
② - 初始化上下文生命周期
③ - 傳播刷新動作至生命周期
④ - 發布上下文刷新完畢事件
⑤ - 構建當前Bean及其依賴關系的快照，設計用於Spring Tool Suite

resetCommonCaches()

主要用於清除Spring內部的緩存

// AbstractApplicationContext.java

protected void resetCommonCaches() {
	ReflectionUtils.clearCache();
	AnnotationUtils.clearCache();
	ResolvableType.clearCache();
	CachedIntrospectionResults.clearClassLoader(getClassLoader());
}