Spring Boot ApplicationContext刷新前的配置

private ConfigurableEnvironment prepareEnvironment(
    SpringApplicationRunListeners listeners,
    ApplicationArguments applicationArguments) {

  // 创建环境对象
  ConfigurableEnvironment environment = getOrCreateEnvironment();

  // 配置环境（包括配置文件加载）
  configureEnvironment(environment, applicationArguments.getSourceArgs());

  // 发布环境准备事件
  listeners.environmentPrepared(environment);

  // 绑定环境到SpringApplication
  bindToSpringApplication(environment);

  return environment;
}

protected ConfigurableApplicationContext createApplicationContext() {
  Class<?> contextClass = this.applicationContextClass;
  if (contextClass == null) {
    try {
      // 根据应用类型选择Context实现
      switch (this.webApplicationType) {
        case SERVLET:
          contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
          break;
        case REACTIVE:
          contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
          break;
        default:
          contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
      }
    }
    catch (ClassNotFoundException ex) {
      // 异常处理
    }
  }
  return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}

private void prepareContext(ConfigurableApplicationContext context,
    ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
    ApplicationArguments applicationArguments, Banner printedBanner) {

  // 设置环境
  context.setEnvironment(environment);

  // 应用后置处理
  postProcessApplicationContext(context);

  // 应用初始化器
  applyInitializers(context);

  // 触发contextPrepared事件
  listeners.contextPrepared(context);

  // 打印启动信息
  if (this.logStartupInfo) {
    logStartupInfo(context.getParent() == null);
    logStartupProfileInfo(context);
  }

  // 注册特定的单例Bean
  context.getBeanFactory().registerSingleton("springApplicationArguments", applicationArguments);
  if (printedBanner != null) {
    context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
  }

  // 加载资源（配置源）
  Set<Object> sources = getAllSources();
  load(context, sources.toArray(new Object[0]));

  // 触发contextLoaded事件
  listeners.contextLoaded(context);
}

public class CustomInitializer
    implements ApplicationContextInitializer<ConfigurableApplicationContext> {

  @Override
  public void initialize(ConfigurableApplicationContext applicationContext) {
    // 添加自定义属性源
    ConfigurableEnvironment env = applicationContext.getEnvironment();
    Map<String, Object> customProperties = new HashMap<>();
    customProperties.put("custom.property", "value");
    env.getPropertySources().addFirst(
      new MapPropertySource("customProperties", customProperties));
  }
}

@Component
public class ApplicationContextPreparer
    implements ApplicationListener<ApplicationContextInitializedEvent> {

  @Override
  public void onApplicationEvent(ApplicationContextInitializedEvent event) {
    ConfigurableApplicationContext context = event.getApplicationContext();
    // 在上下文准备完成后但刷新前执行操作
    System.out.println("ApplicationContext prepared, about to refresh");
  }
}