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<Object> sources = getAllSources();
    Assert.notEmpty(sources, "Sources must not be empty");
    load(context, sources.toArray(new Object[0]));
    listeners.contextLoaded(context);
  }

看一下这里的 load 方法,这里主要把我们的启动类作为 Bean 注册到了 Spring 的容器中。

  protected void load(ApplicationContext context, Object[] sources) {
    if (logger.isDebugEnabled()) {
      logger.debug("Loading source " + StringUtils.arrayToCommaDelimitedString(sources));
    }
    BeanDefinitionLoader loader = createBeanDefinitionLoader(getBeanDefinitionRegistry(context), sources);
    if (this.beanNameGenerator != null) {
      loader.setBeanNameGenerator(this.beanNameGenerator);
    }
    if (this.resourceLoader != null) {
      loader.setResourceLoader(this.resourceLoader);
    }
    if (this.environment != null) {
      loader.setEnvironment(this.environment);
    }
    loader.load();
  }

  /**
   * Load the sources into the reader.
   * @return the number of loaded beans
   */
  int load() {
    int count = 0;
    for (Object source : this.sources) {
      count += load(source);
    }
    return count;
  }

  private int load(Object source) {
    Assert.notNull(source, "Source must not be null");
    if (source instanceof Class<?>) {
      return load((Class<?>) source);
    }
    if (source instanceof Resource) {
      return load((Resource) source);
    }
    if (source instanceof Package) {
      return load((Package) source);
    }
    if (source instanceof CharSequence) {
      return load((CharSequence) source);
    }
    throw new IllegalArgumentException("Invalid source type " + source.getClass());
  }

  private int load(Class<?> source) {
    if (isGroovyPresent() && GroovyBeanDefinitionSource.class.isAssignableFrom(source)) {
      // Any GroovyLoaders added in beans{} DSL can contribute beans here
      GroovyBeanDefinitionSource loader = BeanUtils.instantiateClass(source, GroovyBeanDefinitionSource.class);
      load(loader);
    }
    if (isEligible(source)) {
      this.annotatedReader.register(source);
      return 1;
    }
    return 0;
  }

再来看下 contextLoaded 方法，这里将上下文设置到监听器中，同时也把监听器添加到上下文中。最后发布了一个 ApplicationPreparedEvent 事件。

  public void contextLoaded(ConfigurableApplicationContext context) {
    for (ApplicationListener<?> listener : this.application.getListeners()) {
      if (listener instanceof ApplicationContextAware) {
        ((ApplicationContextAware) listener).setApplicationContext(context);
      }
      context.addApplicationListener(listener);
    }
    this.initialMulticaster.multicastEvent(new ApplicationPreparedEvent(this.application, this.args, context));
  }