本文章基于 Spring 5.3.15

Spring IOC 的核心是 AbstractApplicationContext 的 refresh 方法。

其中一共有 13 个主要方法，这里分析第 5 个：invokeBeanFactoryPostProcessors。

1 AbstractApplicationContext

invokeBeanFactoryPostProcessors(beanFactory)


protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    // 获取 Bean工厂 增强器
    // 执行 Bean工厂 增强器
    PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
    if (!NativeDetector.inNativeImage() && beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
          beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
          beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
    }
}


getBeanFactoryPostProcessors()


/**
 * Bean 工厂增强器集合
 */
private final List<BeanFactoryPostProcessor> beanFactoryPostProcessors = new ArrayList<>();

public List<BeanFactoryPostProcessor> getBeanFactoryPostProcessors() {
   return this.beanFactoryPostProcessors;
}


invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors())

2 PostProcessorRegistrationDelegate

public static void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
   Set<String> processedBeans = new HashSet<>();
   // 对 BeanDefinitionRegistry 类型的处理
   if (beanFactory instanceof BeanDefinitionRegistry) {
      BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
      List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
      List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
      // 硬编码注册的后处理器
      for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
         if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
            BeanDefinitionRegistryPostProcessor registryProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor;
            // 有自定义的方法，需要先调用
            registryProcessor.postProcessBeanDefinitionRegistry(registry);
            registryProcessors.add(registryProcessor);
         } else {
            // 记录常规 BeanFactoryPostProcessor
            regularPostProcessors.add(postProcessor);
         }
      }
      List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
      // 首先，调用实现 PriorityOrdered 的 BeanDefinitionRegistryPostProcessor
      String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
      for (String ppName : postProcessorNames) {
         if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
            currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
            processedBeans.add(ppName);
         }
      }
      // 排序增强器
      sortPostProcessors(currentRegistryProcessors, beanFactory);
      registryProcessors.addAll(currentRegistryProcessors);
      // 调用 Bean 定义注册表增强器
      invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
      currentRegistryProcessors.clear();
      // 其次，调用实现 Ordered 的 BeanDefinitionRegistryPostProcessors
      postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
      for (String ppName : postProcessorNames) {
         if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
            currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
            processedBeans.add(ppName);
         }
      }
      // 排序增强器
      sortPostProcessors(currentRegistryProcessors, beanFactory);
      registryProcessors.addAll(currentRegistryProcessors);
      // 调用 Bean 定义注册表增强器
      invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
      currentRegistryProcessors.clear();
      // 最后, 调用所有其他 BeanDefinitionRegistryPostProcessor 直到不再出现
      boolean reiterate = true;
      while (reiterate) {
         reiterate = false;
         postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
         for (String ppName : postProcessorNames) {
            if (!processedBeans.contains(ppName)) {
               currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
               processedBeans.add(ppName);
               reiterate = true;
            }
         }
         // 排序增强器
         sortPostProcessors(currentRegistryProcessors, beanFactory);
         registryProcessors.addAll(currentRegistryProcessors);
         // 调用 Bean 定义注册表增强器
         invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
         currentRegistryProcessors.clear();
      }
      // 调用 Bean 工厂增强器
      invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
      invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
   } else {
      // 调用向上下文实例注册的工厂处理器
      invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
   }
   // 配置中读取的 BeanFactoryPostProcessor 的处理
   String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
   // 将实现 PriorityOrdered、Ordered 和其余部分的 BeanFactoryPostProcessor 分开
   List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
   List<String> orderedPostProcessorNames = new ArrayList<>();
   List<String> nonOrderedPostProcessorNames = new ArrayList<>();
   // 对后处理器进行分类
   for (String ppName : postProcessorNames) {
      if (processedBeans.contains(ppName)) {
         // 已经处理过则跳过
      }
      else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
         priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
      }
      else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
         orderedPostProcessorNames.add(ppName);
      }
      else {
         nonOrderedPostProcessorNames.add(ppName);
      }
   }
   // 首先，调用实现 PriorityOrdered 的 BeanFactoryPostProcessor
   sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
   invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
   // 接下来，调用实现 Ordered 的 BeanFactoryPostProcessors
   List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
   for (String postProcessorName : orderedPostProcessorNames) {
      orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
   }
   sortPostProcessors(orderedPostProcessors, beanFactory);
   invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
   // 最后，调用所有其他 BeanFactoryPostProcessor
   List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
   for (String postProcessorName : nonOrderedPostProcessorNames) {
      nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
   }
   invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
   // 清除元数据缓存，清除缓存的合并 bean 定义，因为后处理器可能已经修改了原始元数据，例如替换值中的占位符
   beanFactory.clearMetadataCache();
}


sortPostProcessors(currentRegistryProcessors, beanFactory)


private static void sortPostProcessors(List<?> postProcessors, ConfigurableListableBeanFactory beanFactory) {
   if (postProcessors.size() <= 1) {
      return;
   }
   Comparator<Object> comparatorToUse = null;
   if (beanFactory instanceof DefaultListableBeanFactory) {
      comparatorToUse = ((DefaultListableBeanFactory) beanFactory).getDependencyComparator();
   }
   if (comparatorToUse == null) {
      comparatorToUse = OrderComparator.INSTANCE;
   }
   postProcessors.sort(comparatorToUse);
}


invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup())


private static void invokeBeanDefinitionRegistryPostProcessors( Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry, ApplicationStartup applicationStartup) {
   for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
      StartupStep postProcessBeanDefRegistry = applicationStartup.start("spring.context.beandef-registry.post-process").tag("postProcessor", postProcessor::toString);
      postProcessor.postProcessBeanDefinitionRegistry(registry);
      postProcessBeanDefRegistry.end();
   }
}


beanFactory.clearMetadataCache()

3 DefaultListableBeanFactory

public void clearMetadataCache() {
   // 调用父类方法
   super.clearMetadataCache();
   this.mergedBeanDefinitionHolders.clear();
   // 按类型清除缓存
   clearByTypeCache();
}


super.clearMetadataCache()

4 AbstractBeanFactory

public void clearMetadataCache() {
   this.mergedBeanDefinitions.forEach((beanName, bd) -> {
      // 判断 Bean 是否有资格进行元数据缓存
      if (!isBeanEligibleForMetadataCaching(beanName)) {
         bd.stale = true;
      }
   });
}


private final Set<String> alreadyCreated = Collections.newSetFromMap(new ConcurrentHashMap<>(256));

protected boolean isBeanEligibleForMetadataCaching(String beanName) {
   return this.alreadyCreated.contains(beanName);
}

3 DefaultListableBeanFactory

clearByTypeCache()


private void clearByTypeCache() {
   this.allBeanNamesByType.clear();
   this.singletonBeanNamesByType.clear();
}