这个部分的源码看的次数不计其数了，每次看不同开源组件的调用过程中走到这里都有不同的收获。

spring 中 AbstractApplicationContext 的 refresh() 是 spring 的核心，几乎所有的逻辑都在是这里间接被调用。

如下源码为 spring boot 2.7.15 自带的 spring 5.3.29

SpringApplication

通过 WebApplicationType 判断是哪个环境

public enum WebApplicationType {/*** The application should not run as a web application and should not start an* embedded web server.*/NONE,/*** The application should run as a servlet-based web application and should start an* embedded servlet web server.*/SERVLET,/*** The application should run as a reactive web application and should start an* embedded reactive web server.*/REACTIVE;private static final String[] SERVLET_INDICATOR_CLASSES = { "javax.servlet.Servlet","org.springframework.web.context.ConfigurableWebApplicationContext" };private static final String WEBMVC_INDICATOR_CLASS = "org.springframework.web.servlet.DispatcherServlet";private static final String WEBFLUX_INDICATOR_CLASS = "org.springframework.web.reactive.DispatcherHandler";private static final String JERSEY_INDICATOR_CLASS = "org.glassfish.jersey.servlet.ServletContainer";static WebApplicationType deduceFromClasspath() {if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null) && !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)&& !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) {return WebApplicationType.REACTIVE;}for (String className : SERVLET_INDICATOR_CLASSES) {if (!ClassUtils.isPresent(className, null)) {return WebApplicationType.NONE;}}return WebApplicationType.SERVLET;}}

判断逻辑如下

使用响应式的条件是类路径中包含 org.springframework.web.reactive.DispatcherHandler
且不包含 org.springframework.web.servlet.DispatcherServlet 还有org.glassfish.jersey.servlet.ServletContainer

如果类路径不包含 javax.servlet.Servlet，说明不是web程序。

上述情况都不符合，就是 servlet 环境，即 tomcat、undertow、jetty等。

添加了依赖

<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency>

所以，按照 servlet 环境来执行。

public ConfigurableApplicationContext run(String... args) {long startTime = System.nanoTime();DefaultBootstrapContext bootstrapContext = createBootstrapContext();ConfigurableApplicationContext context = null;configureHeadlessProperty();SpringApplicationRunListeners listeners = getRunListeners(args);listeners.starting(bootstrapContext, this.mainApplicationClass);try {ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);configureIgnoreBeanInfo(environment);Banner printedBanner = printBanner(environment);context = createApplicationContext();context.setApplicationStartup(this.applicationStartup);prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);refreshContext(context);afterRefresh(context, applicationArguments);Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);if (this.logStartupInfo) {new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), timeTakenToStartup);}listeners.started(context, timeTakenToStartup);callRunners(context, applicationArguments);}catch (Throwable ex) {handleRunFailure(context, ex, listeners);throw new IllegalStateException(ex);}try {Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime);listeners.ready(context, timeTakenToReady);}catch (Throwable ex) {handleRunFailure(context, ex, null);throw new IllegalStateException(ex);}return context;}

createApplicationContext() 创建上下文

在 spring boot 的 spring.factories 中指定了

# Application Context Factories
org.springframework.boot.ApplicationContextFactory=\
org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext.Factory,\
org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext.Factory

加上当前web 应用类型是 servlet，所以默认创建的是 AnnotationConfigServletWebServerApplicationContext。

最终在 GenericApplicationContext 中创建了 DefaultListableBeanFactory，这个类很重要，其中维护了定义的 bean，方便后面进行注入。

BeanFactory 的最终实现是 DefaultListableBeanFactory

refresh()

public void refresh() throws BeansException, IllegalStateException {synchronized (this.startupShutdownMonitor) {StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");// 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);StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");// Invoke factory processors registered as beans in the context.invokeBeanFactoryPostProcessors(beanFactory);// Register bean processors that intercept bean creation.registerBeanPostProcessors(beanFactory);beanPostProcess.end();// 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();contextRefresh.end();}}
}

容器初始化开始

prepareRefresh()

/*** Prepare this context for refreshing, setting its startup date and* active flag as well as performing any initialization of property sources.*/protected void prepareRefresh() {// Switch to active.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());}}// Initialize any placeholder property sources in the context environment.initPropertySources();// Validate that all properties marked as required are resolvable:// see ConfigurablePropertyResolver#setRequiredPropertiesgetEnvironment().validateRequiredProperties();// 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<>();}

看源码注释，是进行准备工作，有初始化占位符中的变量到上下文环境中，验证必须的属性。

obtainFreshBeanFactory()

/*** Tell the subclass to refresh the internal bean factory.* @return the fresh BeanFactory instance* @see #refreshBeanFactory()* @see #getBeanFactory()*/protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {refreshBeanFactory();return getBeanFactory();}

由于上面已经进行了 beanFactory  的创建处理，可以直接可以获取到对应的对象。

prepareBeanFactory()

/*** Configure the factory's standard context characteristics,* such as the context's ClassLoader and post-processors.* @param beanFactory the BeanFactory to configure*/protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {// Tell the internal bean factory to use the context's class loader etc.beanFactory.setBeanClassLoader(getClassLoader());if (!shouldIgnoreSpel) {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.ignoreDependencyInterface(ApplicationStartupAware.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 (!NativeDetector.inNativeImage() && 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());}if (!beanFactory.containsLocalBean(APPLICATION_STARTUP_BEAN_NAME)) {beanFactory.registerSingleton(APPLICATION_STARTUP_BEAN_NAME, getApplicationStartup());}}

对 beanFactory 进行一系列设置。

postProcessBeanFactory()

/*** Modify the application context's internal bean factory after its standard* initialization. The initial definition resources will have been loaded but no* post-processors will have run and no derived bean definitions will have been* registered, and most importantly, no beans will have been instantiated yet.* <p>This template method allows for registering special BeanPostProcessors* etc in certain AbstractApplicationContext subclasses.* @param beanFactory the bean factory used by the application context*/protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {}

看文档注释，用于 beanFactory 标准初始化后的应用上下文内部修改操作。

用法参考

https://blog.csdn.net/qq_35971258/article/details/128222426

至此，BeanDefinition 处理完成。接下来是 bean 的获取，即依赖注入。

依赖注入

invokeBeanFactoryPostProcessors()

/*** Instantiate and invoke all registered BeanFactoryPostProcessor beans,* respecting explicit order if given.* <p>Must be called before singleton instantiation.*/

看注释含义是实例化并且调用所有注册的 BeanFactoryPostProcessor 相关 bean。

具体作用还未深入过

https://www.cnblogs.com/sishang/p/6588542.html

registerBeanPostProcessors()

给 beanFactory 添加 BeanPostProcessor，用于前置后置处理。

通过 postProcessBeforeInitialization() 和 postProcessAfterInitialization() 实现。

其他操作

initMessageSource()

还未深入过

initApplicationEventMulticaster()
 

跟事件相关的，还未深入过

onRefresh()

看英文意思，初始化其他指定 bean 在特殊上下文

使用的地方有 servlet 容器初始化，例如 tomcat 启动前的准备工作在这里执行。

在 ServletWebServerApplicationContext 中进行重写，注册相关的单例到 beanFactory 中。方便后面接下来的 servlet 容器启动操作。

Lifecycle 用于启动或停止操作的通用接口，这里使用的实现类 WebServerStartStopLifecycle。通过实现类间接调用 WebServer 接口的实现类实现对应的 web 服务器的启动或停止操作。

servlet 容器的相关操作通过接口 WebServer 进行抽象，对应的实现有

registerListeners()

注册监听，观察者模式

finishBeanFactoryInitialization()

初始化落下的单例 bean。

finishRefresh()

servlet 容器的启动和停止操作

通过接口 LifecycleProcessor 的实现类 DefaultLifecycleProcessor 调用 WebServerStartStopLifecycle 执行相关操作。

其中，bean 获取在 AbstractBeanFactory 中实现，单例调用了 DefaultSingletonBeanRegistry 的 getSingleton() 单独处理，最终创建 bean 还是通过 AbstractAutowireCapableBeanFactory 的 createBean() 来实现。