Spring Boot 完整启动流程详解

public static ConfigurableApplicationContext run(Class<?> primarySource, String[] args) {
    return new SpringApplication(primarySource).run(args);
}

StopWatch stopWatch = new StopWatch();
stopWatch.start();

SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting(); // 发布ApplicationStartingEvent

ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArgs);

graph TD
    A[创建Environment对象] --> B[加载配置源]
    B --> C[解析Profile配置]
    C --> D[转换配置属性]
    D --> E[发布ApplicationEnvironmentPreparedEvent]

Banner printedBanner = printBanner(environment);

context = createApplicationContext();

protected ConfigurableApplicationContext createApplicationContext() {
    return switch (this.webApplicationType) {
        case SERVLET -> new AnnotationConfigServletWebServerApplicationContext();
        case REACTIVE -> new AnnotationConfigReactiveWebServerApplicationContext();
        default -> new AnnotationConfigApplicationContext(); // 非Web应用
    };
}

prepareContext(context, environment, listeners, appArgs, printedBanner);

refreshContext(context); // 内部调用Spring的refresh()

public void refresh() {
    // 1. 准备刷新
    prepareRefresh();
    // 2. 获取BeanFactory
    ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
    // 3. 准备BeanFactory
    prepareBeanFactory(beanFactory);
    try {
        // 4. 后置处理BeanFactory
        postProcessBeanFactory(beanFactory);
        // 5. ★★★ 执行BeanFactoryPostProcessor（自动配置入口）
        invokeBeanFactoryPostProcessors(beanFactory);
        // 6. 注册BeanPostProcessor
        registerBeanPostProcessors(beanFactory);
        // 7. 初始化消息源
        initMessageSource();
        // 8. 初始化事件广播器
        initApplicationEventMulticaster();
        // 9. ★ Web容器启动关键步骤
        onRefresh();
        // 10. 注册监听器
        registerListeners();
        // 11. ★★★ 实例化所有非延迟单例Bean
        finishBeanFactoryInitialization(beanFactory);
        // 12. 完成刷新
        finishRefresh();
    } catch (BeansException ex) {
        // 异常处理...
    }
}

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(
        beanFactory, getBeanFactoryPostProcessors());
    // 这里会处理@SpringBootApplication->加载自动配置类
}

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

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
    // 初始化所有非延迟单例Bean
    beanFactory.preInstantiateSingletons();
}

afterRefresh(context, appArgs);

stopWatch.stop();
listeners.started(context); // ApplicationStartedEvent
callRunners(context, appArgs); // 执行ApplicationRunner/CommandLineRunner
listeners.running(context); // ApplicationReadyEvent

private void callRunners(ApplicationContext context, ApplicationArguments args) {
    List<Object> runners = new ArrayList<>();
    runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
    runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
    AnnotationAwareOrderComparator.sort(runners);
    for (Object runner : runners) {
        if (runner instanceof ApplicationRunner) {
            ((ApplicationRunner) runner).run(args);
        }
        if (runner instanceof CommandLineRunner) {
            ((CommandLineRunner) runner).run(args.getSourceArgs());
        }
    }
}

graph TD
    A[SpringApplication.run] --> B[启动计时器]
    B --> C[初始化监听器]
    C --> D[发布StartingEvent]
    D --> E[准备Environment]
    E --> F[打印Banner]
    F --> G[创建上下文]
    G --> H[预处理上下文]
    H --> I[refreshContext核心]
    I --> J[后置处理]
    J --> K[发布StartedEvent]
    K --> L[执行Runner]
    L --> M[发布ReadyEvent]