SpringIOCrefresh()初始化代码实例

/* org/springframework/context/support/AbstractApplicationContext.java:870 */
  protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {//初始化容器的conversionService
    if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
        beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
      beanFactory.setConversionService(
          beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
    }
//如果没有任何一个类似PropertyPlaceholderConfigurer bean处理器
    //默认一个嵌入式值解析器，主要是为了解析属性值例如数据库连接中${password}等属性解析
    if (!beanFactory.hasEmbeddedValueResolver()) {
      beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
    }
// 先实例化LoadTimeWeaverAware相关的beans，以便尽早转换，AOP相关
    String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
    for (String weaverAwareName : weaverAwareNames) {
      getBean(weaverAwareName);
    }

//删除临时类加载器，停止临时类加载器进行类型匹配
    beanFactory.setTempClassLoader(null);

//拷贝beandefinitionNames到frozenBeanDefinitionNames
    beanFactory.freezeConfiguration();

    // 实例化所有不需要延迟初始化的单例bean
    beanFactory.preInstantiateSingletons();
  }

/* org/springframework/beans/factory/support/DefaultListableBeanFactory.java:885 */
  public void preInstantiateSingletons() throws BeansException {
    if (logger.isTraceEnabled()) {
      logger.trace("Pre-instantiating singletons in " + this);
    }

    // Iterate over a copy to allow for init methods which in turn register new bean definitions.
    // While this may not be part of the regular factory bootstrap, it does otherwise work fine.
    //拷贝beanDefinitionNames副本，考虑到遍历中其他线程可能修改beandefinitionNames
    // ArrayList类型遍历时规避fast-fail，实现fast-safe
    List beanNames = new ArrayList<>(this.beanDefinitionNames);

    // Trigger initialization of all non-lazy singleton beans...
    for (String beanName : beanNames) {
      //当bean存在parentBean时的继承关系
      //① bean不存在parentBean时，创建一个new RootBeanDefinition(beandefinition)返回。
      //② bean存在parentBean时，支持继承关系
      // 需要先创建parentBean的new RootBeanDefinition(parentBeanDefinition)
      // 然后用beandefinition覆盖parentBean的RootBeanDefinition的相关属性并返回。superBean.overrideFrom(subBean);
      RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
      //用mergedLocalBeanDefinition判断是否需要初始化
      //筛选不是抽象类且不是延迟实例化的单例进行初始化
      if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
        if (isFactoryBean(beanName)) {
          //工厂Bean beanName=&beanName
          Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
          if (bean instanceof FactoryBean) {
            final FactoryBean<?> factory = (FactoryBean<?>) bean;
            boolean isEagerInit;
            if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
              isEagerInit = AccessController.doPrivileged((PrivilegedAction)
                      ((SmartFactoryBean<?>) factory)::isEagerInit,
                  getAccessControlContext());
            }
            else {
              isEagerInit = (factory instanceof SmartFactoryBean &&
                  ((SmartFactoryBean<?>) factory).isEagerInit());
            }
            if (isEagerInit) {
              getBean(beanName);
            }
          }
        }
        else {
          //不是工厂bean 直接初始化
          getBean(beanName);
        }
      }
    }

    //SmartInitializingSingleton类型的单例初始化后的回调
    for (String beanName : beanNames) {
      Object singletonInstance = getSingleton(beanName);
      if (singletonInstance instanceof SmartInitializingSingleton) {
        final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
        if (System.getSecurityManager() != null) {
          AccessController.doPrivileged((PrivilegedAction