Spring IOC 的核心是 AbstractApplicationContext 的 refresh 方法。
其中一共有 13 個主要方法，這裡分析第 11 個：finishBeanFactoryInitialization。

1 AbstractApplicationContext

1-1 初始化剩下的單例項

finishBeanFactoryInitialization(beanFactory)

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
   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));
   }
   if (!beanFactory.hasEmbeddedValueResolver()) {
      beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
   }
   String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
   for (String weaverAwareName : weaverAwareNames) {
      getBean(weaverAwareName);
   }
   beanFactory.setTempClassLoader(null);
   // 凍結所有的 bean 定義，說明註冊的 bean 定義將不被修改或任何進一步的處理
   beanFactory.freezeConfiguration();
   // 初始化剩下的單例項（非惰性的）
   beanFactory.preInstantiateSingletons();
}
 

1-2 凍結所有的 bean 定義

beanFactory.freezeConfiguration()

2 DefaultListableBeanFactory

public void freezeConfiguration() {
   this.configurationFrozen = true;
   this.frozenBeanDefinitionNames = StringUtils.toStringArray(this.beanDefinitionNames);
}

1 AbstractApplicationContext

1-2 初始化剩下的單例項

beanFactory.preInstantiateSingletons()
 

2 DefaultListableBeanFactory

public void preInstantiateSingletons() throws BeansException {
   if (logger.isTraceEnabled()) {
      logger.trace("Pre-instantiating singletons in " + this);
   }
   List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
   for (String beanName : beanNames) {
      RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
      if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
         if (isFactoryBean(beanName)) {
            Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
            if (bean instanceof FactoryBean) {
               FactoryBean<?> factory = (FactoryBean<?>) bean;
               boolean isEagerInit;
               if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                  isEagerInit = AccessController.doPrivileged(
                        (PrivilegedAction<Boolean>) ((SmartFactoryBean<?>) factory)::isEagerInit,
                        getAccessControlContext());
               }
               else {
                  isEagerInit = (factory instanceof SmartFactoryBean &&
                        ((SmartFactoryBean<?>) factory).isEagerInit());
               }
               if (isEagerInit) {
                  getBean(beanName);
               }
            }
         }
         else {
            getBean(beanName);
         }
      }
   }
   for (String beanName : beanNames) {
      Object singletonInstance = getSingleton(beanName);
      if (singletonInstance instanceof SmartInitializingSingleton) {
         StartupStep smartInitialize = this.getApplicationStartup().start("spring.beans.smart-initialize").tag("beanName", beanName);
         SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
         if (System.getSecurityManager() != null) {
            AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
               smartSingleton.afterSingletonsInstantiated();
               return null;
            }, getAccessControlContext());
         }
         else {
            smartSingleton.afterSingletonsInstantiated();
         }
         smartInitialize.end();
      }
   }
}