AbstractApplicationContext的refresh流程

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AbstractApplicationContext 是 ApplicationContext 的一个抽象实现类。和普通的 BeanFactory 不同的是，ApplicationContext 可以检测到它的内部 BeanFactory 中定义的特殊 Bean：自动完成 BeanFactoryPostProcessor、BeanPostProcessor、ApplicationListener 的注册。

按照惯例，先来看下 AbstractApplicationContext 的继承结构，嗯，你会发现挺复杂的

image-20200411182520072

不过不要紧，我们只关心它的 refresh 方法实现。refresh 方法来自 ConfigurableApplicationContext 接口，关于它的功能描述如下：

加载或刷新配置的持久化，这些配置可以来自 XML 文件、properties 文件、关心数据库等等。因为该方法是一个启动方法，如果失败了，它应该销毁已经创建的单例，以避免出现悬挂资源（dangling resources），换句话说，要么实例化所有的单例，要么一个也不实例化。

refresh 代码跟踪

接下来看下 refresh 方法的实现。

prepareRefresh

这里是做一些准备工作，包括设置开始时间、active 状态、PropertySources 的初始化等等

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protected void prepareRefresh() {
   this.startupDate = System.currentTimeMillis();
   this.closed.set(false);
   this.active.set(true);

   // Initialize any placeholder property sources in the context environment
   initPropertySources();

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

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

obtainFreshBeanFactory

告诉子类刷新内部的 BeanFactory，然后返回刷新后的 BeanFactory

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refreshBeanFactory();
return getBeanFactory();

GenericApplicationContext 中的 refreshBeanFactory 实现如下：

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protected final void refreshBeanFactory() throws IllegalStateException {
   if (!this.refreshed.compareAndSet(false, true)) {
      throw new IllegalStateException(
            "GenericApplicationContext does not support multiple refresh attempts: just call 'refresh' once");
   }
   this.beanFactory.setSerializationId(getId());
}

它只是设置下 SerializationId，实际的 beanFactory 初始化是在创建时完成的

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public GenericApplicationContext() {
   this.beanFactory = new DefaultListableBeanFactory();
}

当然 refreshBeanFactory 也可以有其他的实现方式。

getBeanFactory 比较简单，就是返回已创建的 beanFactory

prepareBeanFactory

配置 BeanFactory 的标准 context 特征，例如设置 context 的 class loader 和 post processor

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protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
   // 内部的 BeanFactory 使用 context 的 class loader
   beanFactory.setBeanClassLoader(getClassLoader());
   beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
   beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

   // 这家伙就是用来处理 Aware 接口的
   beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
   // 忽略这些 Aware 接口，BeanFactory 中有单独的处理逻辑
   beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
   beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
   beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
   beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
   beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
   beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

   // 这几个不是 BeanFactory 中定义的 bean，需要特殊处理
   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()));
   }

   // 注册默认的环境相关的 bean
   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());
   }
}

postProcessBeanFactory

对 BeanFactory 进行后处理，默认的实现为空，交给子类去扩展。可以对 beanFactory 进行想要的操作。比如 GenericWebApplicationContext 的实现如下：

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protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
   if (this.servletContext != null) {
      beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext));
      beanFactory.ignoreDependencyInterface(ServletContextAware.class);
   }
   WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext);
   WebApplicationContextUtils.registerEnvironmentBeans(beanFactory, this.servletContext);
}

invokeBeanFactoryPostProcessors

调用 BeanFactoryPostProcessor

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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()));
   }
}

首先通过 getBeanFactoryPostProcessors 方法取出已经注册到 BeanFactory 中的所有BeanFactoryPostProcessor，然后交给 invokeBeanFactoryPostProcessors 方法去处理

处理流程

主要分为两个阶段：首先处理 BeanDefinitionRegistryPostProcessor 接口的回调，然后处理 BeanFactoryPostProcessor 接口的回调

BeanDefinitionRegistryPostProcessor 接口回调

这是第一个阶段，处理实现了 BeanDefinitionRegistryPostProcessor 接口的 bean 的回调。

判断 beanFactory 是否为 BeanDefinitionRegistry 类型的实例

是 BeanDefinitionRegistry 类型的实例

首先处理方法入参中传入的 beanFactoryPostProcessors，分别调用其 postProcessBeanDefinitionRegistry 方法

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for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
   // 是 BeanDefinitionRegistryPostProcessor
   if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
      BeanDefinitionRegistryPostProcessor registryProcessor =
            (BeanDefinitionRegistryPostProcessor) postProcessor;
      // 调用 postProcessBeanDefinitionRegistry 方法
      registryProcessor.postProcessBeanDefinitionRegistry(registry);
      registryProcessors.add(registryProcessor);
   }
   // 是普通的 BeanFactoryPostProcessor，留作后面统一处理
   else {
      regularPostProcessors.add(postProcessor);
   }
}

然后从 beanFactory 中获取所有实现了 BeanDefinitionRegistryPostProcessor 接口和 PriorityOrdered 接口的 bean，分别调用其 postProcessBeanDefinitionRegistry 方法

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// 取出所有实现了 BeanDefinitionRegistryPostProcessor接口的beanName
String[] postProcessorNames =
      beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
   // 如果还实现了PriorityOrdered接口
   if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
      // 取出bean
      currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
      processedBeans.add(ppName);
   }
}
// 排序
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);

// 调用postProcessBeanDefinitionRegistry方法
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
// 清理
currentRegistryProcessors.clear();

接着是 beanFactory 中实现了 BeanDefinitionRegistryPostProcessor 接口和 Ordered 接口的 bean，分别调用其 postProcessBeanDefinitionRegistry 方法

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// 取出所有实现了 BeanDefinitionRegistryPostProcessor接口的beanName
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
   // 如果还未处理过，并且实现了Ordered接口
   if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
      // 取出bean
      currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
      processedBeans.add(ppName);
   }
}
// 排序
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
// 调用postProcessBeanDefinitionRegistry方法
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();

最后是其他实现了 BeanDefinitionRegistryPostProcessor 接口且还未处理过的 bean，分别调用其 postProcessBeanDefinitionRegistry 方法

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boolean reiterate = true;
while (reiterate) {
   reiterate = false;
   // 取出所有实现了 BeanDefinitionRegistryPostProcessor接口的beanName
   postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
   for (String ppName : postProcessorNames) {
      // 只要是还未处理过的
      if (!processedBeans.contains(ppName)) {
         // 取出bean
         currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
         processedBeans.add(ppName);
         reiterate = true;
      }
   }
   sortPostProcessors(currentRegistryProcessors, beanFactory);
   // 排序
   registryProcessors.addAll(currentRegistryProcessors);
   // 调用postProcessBeanDefinitionRegistry方法
   invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
   currentRegistryProcessors.clear();
}

因为 BeanDefinitionRegistryPostProcessor接口 继承自 BeanFactoryPostProcessor 接口，所以还需要回调 BeanFactoryPostProcessor 接口的 postProcessBeanFactory 方法

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invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
不是 BeanDefinitionRegistry 类型的实例

这个就比较简单了，直接调用 BeanFactoryPostProcessor 的 postProcessBeanFactory 方法

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for (BeanFactoryPostProcessor postProcessor : postProcessors) {
   postProcessor.postProcessBeanFactory(beanFactory);
}

BeanFactoryPostProcessor 接口回调

这里说的 BeanFactoryPostProcessor 不包括接口入参的 beanFactoryPostProcessors，因为在上一步已经处理过了。也不包括 beanFactory 中实现了 BeanDefinitionRegistryPostProcessor 接口的 bean，这种情况也在上一步处理过了。

首先还是要从 beanFactory 中取出所有实现了 BeanFactoryPostProcessor 接口的 beanName

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// 取出所有的BeanFactoryPostProcessor的beanName
String[] postProcessorNames =
      beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

按照是否实现了 PriorityOrdered、Ordered 接口分为 3 类

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List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
List<String> orderedPostProcessorNames = new ArrayList<>();
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
for (String ppName : postProcessorNames) {
   if (processedBeans.contains(ppName)) {
      // 忽略已经在第一阶段被postProcessBeanDefinitionRegistry处理过的
   }
   else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
      // 实现了PriorityOrdered接口的
      priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
   }
   else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
      // 实现了Ordered接口的
      orderedPostProcessorNames.add(ppName);
   }
   else {
      // 未实现优先级接口的
      nonOrderedPostProcessorNames.add(ppName);
   }
}

先回调实现了 PriorityOrdered 接口的

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sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

接着是回调实现了 Ordered 接口的

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List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>();
for (String postProcessorName : orderedPostProcessorNames) {
   orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
sortPostProcessors(orderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

最后是未实现优先级接口的

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

registerBeanPostProcessors

实例化并且调用所有已注册的 BeanPostProcessor

获取所有实现了 BeanPostProcessor 接口的 beanName

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

按照是否实现了 PriorityOrdered、Ordered 接口分为 3 类，实现了 MergedBeanDefinitionPostProcessor 接口单独拎出来，用于特殊处理

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for (String ppName : postProcessorNames) {
   if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
      BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
      priorityOrderedPostProcessors.add(pp);

      // MergedBeanDefinitionPostProcessor 接口由 spring 内部处理
      if (pp instanceof MergedBeanDefinitionPostProcessor) {
         internalPostProcessors.add(pp);
      }
   }
   else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
      orderedPostProcessorNames.add(ppName);
   }
   else {
      nonOrderedPostProcessorNames.add(ppName);
   }
}

先注册所有实现了 PriorityOrdered 接口的

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sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

再注册实现了 Ordered 接口的

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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);

最后注册所有实现了 MergedBeanDefinitionPostProcessor 接口的

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sortPostProcessors(internalPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, internalPostProcessors);

initMessageSource

对 messageSource 进行初始化

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ConfigurableListableBeanFactory beanFactory = getBeanFactory();
// beanFactory 中已经注册过 messageSource 了
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());
      }
   }
}
// 还未注册过
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);
}

initApplicationEventMulticaster

初始化上下文中的事件机制

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protected void initApplicationEventMulticaster() {
   ConfigurableListableBeanFactory beanFactory = getBeanFactory();
   // beanFactory 中已经注册过 applicationEventMulticaster
   if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
      this.applicationEventMulticaster =
            beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
   }
   // 还未注册过
   else {
      this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
      beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
   }
}

onRefresh

留给子类去实现，用于初始化其他特殊的 bean。比如 Spring Boot 中，ServletWebServerApplicationContext 就是在这一步去创建的 web server

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protected void onRefresh() {
   super.onRefresh();
   try {
      createWebServer();
   }
   catch (Throwable ex) {
      throw new ApplicationContextException("Unable to start web server", ex);
   }
}

ServletWebServerApplicationContext 创建 web server

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

registerListeners

检查 listener bean 并向容器注册

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// 先注册 AbstractApplicationContext 中取到的
for (ApplicationListener<?> listener : getApplicationListeners()) {
   getApplicationEventMulticaster().addApplicationListener(listener);
}

// 不要在此初始化 FactoryBeans（最后一个参数设置为false），需要留给 post-processors 处理
String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
for (String listenerBeanName : listenerBeanNames) {
   getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
}

// 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);
   }
}

finishBeanFactoryInitialization

完成当前 context 的 beanFactory 的初始化，初始化剩下所有的 singleton bean

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// 初始化 conversionService
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));
}

// 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));
}

// 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);
}

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

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

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

finishRefresh

完成当前 context 的 refresh 操作，调用 LifecycleProcessor 的 onRefresh 方法，发布 ContextRefreshedEvent 事件

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// Clear context-level resource caches (such as ASM metadata from scanning).
clearResourceCaches();

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

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

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

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

整体流程

整体流程如下图所示：

image-20200418012104632

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