SpringBoot 创建容器的实现

spring 容器的创建对应 SpringApplication 中 run 中调用的 createApplicationContext 方法。这里创建了一个 web 容器，接下就进去 prepareContext 容器准备阶段：

  private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment,
      SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
    //为容器设置环境
    context.setEnvironment(environment);
    //这里的空实现留给开发者扩展，设置数据转换的ConversionService
    postProcessApplicationContext(context);
    //执行容器中的 Initializers 的 initialize 方法
    applyInitializers(context);
    listeners.contextPrepared(context);
    if (this.logStartupInfo) {
      logStartupInfo(context.getParent() == null);
      logStartupProfileInfo(context);
    }
    // Add boot specific singleton beans
    ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
    beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
    if (printedBanner != null) {
      beanFactory.registerSingleton("springBootBanner", printedBanner);
    }
    if (beanFactory instanceof DefaultListableBeanFactory) {
      ((DefaultListableBeanFactory) beanFactory)
          .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
    }
    if (this.lazyInitialization) {
      context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
    }
    // Load the sources
    Set