spring源码解析之ConfigurationClassPostProcessor分析

ConfigurationClassPostProcessor是spring框架中非常重要的一个PostProcessor，尤其是现在的项目基本上都是使用springboot和springcloud，那么更加离不开它。我们先来看看它实现了哪些功能

1.@Bean

2.@Import

3.@ComponentScan/@ComponentScans

4.@ImportResource

5.@PropertySource

你没有看错，上述的功能都是基于这个PostProcessor来实现的，如果你还不了解，那么跟我一起来探索吧，在阅读之前，希望对spring的ioc有一定的了解更佳。

一、ConfigurationClassPostProcessor类图

从这个图上面我们可以看到它实现了BeanDefinitionRegistryPostProcessor、PriorityOrdered知道这一点比较重要，后面会提到。

二、流程图

这个流程图的入口是如下代码

AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfig.class);

其中MainConfig是配置类，大家可自行编写，感兴趣的可以自己对着这个流程图进行debug分析。下面开始对上述的流程图核心逻辑进行分析。

流程1-7注册PostProcessor、配置类MainConfig，比较不详细讲了，只贴一下关键的代码做解释

1.AnnotationConfigUtils#registerAnnotationConfigProcessors()

public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
      BeanDefinitionRegistry registry, @Nullable Object source) {
   

   DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
   if (beanFactory != null) {
   
      if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
   
         beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
      }
      if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
   
         beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
      }
   }

   Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);

    //1.这里就是注册ConfigurationClassPostProcessor
   if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
   
      RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
   }

   if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
   
      RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
   }

   // Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
   if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
   
      RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
   }

   // Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
   if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
   
      RootBeanDefinition def = new RootBeanDefinition();
      try {
   
         def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
               AnnotationConfigUtils.class.getClassLoader()));
      }
      catch (ClassNotFoundException ex) {
   
         throw new IllegalStateException(
               "Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
      }
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
   }

   if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
   
      RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
   }

   if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
   
      RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
      def.setSource(source);
      beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
   }

   return beanDefs;
}

这里虽然很多，但是非常简单，主要的目的就是将一些需要PostProcessor封装成BeanDefinition，然后注册。我们知道spring实例化bean都是将需要实例化的bean先封装成BeanDefinition。比如我们ConfigurationClassPostProcessor就是在这个地方加入的，还有其他的postProcessor，感兴趣的可以自行研究，这里主要研究ConfigurationClassPostProcessor

2.AnnotatedBeanDefinitionReader#doRegisterBean()

private <T> void doRegisterBean(Class<T> beanClass, @Nullable String name,
      @Nullable Class<? extends Annotation>[] qualifiers, @Nullable Supplier<T> supplier,
      @Nullable BeanDefinitionCustomizer[] customizers) {
   

   AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(beanClass);
   if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
   
      return;
   }

   abd.setInstanceSupplier(supplier);
   ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
   abd.setScope(scopeMetadata.getScopeName());
   String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));

   AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
   if (qualifiers != null) {
   
      for (Class<? extends Annotation> qualifier : qualifiers) {
   
         if (Primary.class == qualifier) {
   
            abd.setPrimary(true);
         }
         else if (Lazy.class == qualifier) {
   
            abd.setLazyInit(true);
         }
         else {
   
            abd.addQualifier(new AutowireCandidateQualifier(qualifier));
         }
      }
   }
   if (customizers != null) {
   
      for (BeanDefinitionCustomizer customizer : customizers) {
   
         customizer.customize(abd);
      }
   }

   BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
   definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
   BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
}

这里是从AnnotationConfigApplicationContext#register()方法进来的，主要是注册配置类，比如：new AnnotationConfigApplicationContext(MainConfig.class)我是从这个入口进来的，那么这里就是注册MainConfig，也是先封装成BeanDefinition。到这里我们至少是有两个BeanDefinition（还有其他），一个是MainConfig一个是ConfigurationClassPostProcessor。

我们继续开始spring的核心流程了refresh方法了，这里也是讲主要的流程，大家可以根据上面的流程图自行分析其他流程。接下来我们从refresh()方法中的invokeBeanFactoryPostProcessors()开始，这个方法最终会到PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors

3.PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors

public static void invokeBeanFactoryPostProcessors(
      ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
   

   // Invoke BeanDefinitionRegistryPostProcessors first, if any.
   Set<String> processedBeans = new HashSet<>();

   if (beanFactory instanceof BeanDefinitionRegistry) {
   
      BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
      List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
      List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();

      for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
   
         if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
   
            BeanDefinitionRegistryPostProcessor registryProcessor =
                  (BeanDefinitionRegistryPostProcessor) postProcessor;
            registryProcessor.postProcessBeanDefinitionRegistry(registry);
            registryProcessors.add(registryProcessor);
         }
         else {
   
            regularPostProcessors.add(postProcessor);
         }
      }

      // Do not initialize FactoryBeans here: We need to leave all regular beans
      // uninitialized to let the bean factory post-processors apply to them!
      // Separate between BeanDefinitionRegistryPostProcessors that implement
      // PriorityOrdered, Ordered, and the rest.
      List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

      // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
      String[] postProcessorNames =
            beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
       //1.ConfigurationClassPostProcessor会在这里实例化
      for (String ppName : postProcessorNames) {
   
         if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
   
            currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
            processedBeans.add(ppName);
         }
      }
      sortPostProcessors(currentRegistryProcessors, beanFactory);
      registryProcessors.addAll(currentRegistryProcessors);
       //2.实例化之后会调用ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry
      invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
      currentRegistryProcessors.clear();

      // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
      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);
         }
      }
      sortPostProcessors(currentRegistryProcessors, beanFactory);
      registryProcessors.addAll(currentRegistryProcessors);
      invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
      currentRegistryProcessors.clear();

      // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
      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;
            }
         }
         sortPostProcessors(currentRegistryProcessors, beanFactory);
         registryProcessors.addAll(currentRegistryProcessors);
         invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
         currentRegistryProcessors.clear();
      }

      // Now, invoke the postProcessBeanFactory callback of all processors handled so far.
      invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
      invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
   }

   else {
   
      // Invoke factory processors registered with the context instance.
      invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
   }

   // Do not initialize FactoryBeans here: We need to leave all regular beans
   // uninitialized to let the bean factory post-processors apply to them!
   String[] postProcessorNames =
         beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

   // Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
   // Ordered, and the rest.
   List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
   List<String> orderedPostProcessorNames = new ArrayList<>();
   List<String> nonOrderedPostProcessorNames = new ArrayList<>();
   for (String ppName : postProcessorNames) {
   
      if (processedBeans.contains(ppName)) {
   
         // skip - already processed in first phase above
      }
      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);
      }
   }

   // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
   sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
   invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

   // Next, invoke the BeanFactoryPostProcessors that implement Ordered.
   List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
   for (String postProcessorName : orderedPostProcessorNames) {
   
      orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
   }
   sortPostProcessors(orderedPostProcessors, beanFactory);
   invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

   // Finally, invoke all other BeanFactoryPostProcessors.
   List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
   for (String postProcessorName : nonOrderedPostProcessorNames) {
   
      nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
   }
   invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

   // Clear cached merged bean definitions since the post-processors might have
   // modified the original metadata, e.g. replacing placeholders in values...
   beanFactory.clearMetadataCache();
}

这里算是spring里面重要的思想，spring在实例化bean的时候会有先后顺序，整体的顺序如下

1、先实例化BeanFactoryPostProcessor

2、再实例化BeanPostProcessor

3、最后再实例化普通的bean

其中上述上面每个细节又会根据是否是否实现PriorityOrdered、Ordered等排序，那么spring为什么会这么做呢？个人理解如下：

1、BeanFactoryPostProcessor主要就是再生成bean，所以排最前面

2、BeanPostProcessor主要是bean实例化前后做拦截作用，所以它又比普通的bean早实例化，否则它都没实例化出来怎么去拦截处理其他的类

3、PriorityOrdered、Ordered表示又做了一次先后顺序，比如优先级高的实例化之后，可以拦截优先级更低的bean，所以普通的bean实例化会被所有的BeanPostProcessor拦截处理。

上面的方法的主要主要是先实例化BeanFactoryPostProcessor。因为从上面的ConfigurationClassPostProcessor类图中，我们可以看到它实现了BeanDefinitionRegistryPostProcessor、PriorityOrdered接口。

所以我们看上面代码的注释1和注释2，其他的部分感兴趣自行阅读

注释1：会实例化ConfigurationClassPostProcessor(当然同样实现了BeanDefinitionRegistryPostProcessor、PriorityOrdered接口都会被实例化)，实例化的逻辑和普通的对象实例化一样，没什么区别

注释2：会调用BeanDefinitionRegistryPostProcessor#postProcessBeanDefinitionRegistry()代码如下

private static void invokeBeanDefinitionRegistryPostProcessors(
      Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry) {
   

   for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
   
      postProcessor.postProcessBeanDefinitionRegistry(registry);
   }
}

所以接下来就会进入到ConfigurationClassPostProcessor#postProcessBeanDefinitionRegistry这个才是我们今天的主角

4.ConfigurationClassPostProcessor#postProcessBeanDefinitionRegistry()

@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
   
   int registryId = System.identityHashCode(registry);
   //...省略代码
   processConfigBeanDefinitions(registry);
}

5.processConfigBeanDefinitions()

public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
   
   List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
   String[] candidateNames = registry.getBeanDefinitionNames();

   //1....省略代码部分代码start
    //省略的部分就是找到被@Configuration标注的类，然后加入到configCandidates集合中
    //1...省略部分代码end

   // Parse each @Configuration class
   ConfigurationClassParser parser = new ConfigurationClassParser(
         this.metadataReaderFactory, this.problemReporter, this.environment,
         this.resourceLoader, this.componentScanBeanNameGenerator, registry);

   Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);
   Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());
   do {
   
       //2.这里是核心逻辑，解析被@Configuration标注的类
      parser.parse(candidates);
      //...省略代码
       //3.生成beanDefinition注册
      this.reader.loadBeanDefinitions(configClasses);
      //....省略代码
}

上述方法三个核心的逻辑，上面已经写了比较清洗的注释，其中最重要的逻辑就是注释2，这里面包含了@Bean、@ComponentScan、@Import的所有的实现逻辑。以咱们这个例子为例，configCandidates集合中只有MainConfig（其实是BeanDifinition）。接下来我们看parse()

6.ConfigurationClassParser.parse()

protected final void parse(@Nullable String className, String beanName) throws IOException {
   
   Assert.notNull(className, "No bean class name for configuration class bean definition");
   MetadataReader reader = this.metadataReaderFactory.getMetadataReader(className);
   processConfigurationClass(new ConfigurationClass(reader, beanName), DEFAULT_EXCLUSION_FILTER);
}

上面还省略了一个parse方法，那里面比较简单只有for循环，我就直接略过了，直接到这个parse方法。这里只有几行代码，但是我们注意一下ConfigurationClass，这个类比较重要，一个ConfigClass实例（比如本文MainConfig）对应一个ConfigurationClass实例，最终spring会将@Import、@Bean等信息解析到该类的属性中。我们先看下这个类有哪些属性，让大家现有一个印象

final class ConfigurationClass {
   

   private final AnnotationMetadata metadata;

   private final Resource resource;

   @Nullable
   private String beanName;

   private final Set<ConfigurationClass> importedBy = new LinkedHashSet<>(1);

   private final Set<BeanMethod> beanMethods = new LinkedHashSet<>();

   private final Map<String, Class<? extends BeanDefinitionReader>> importedResources =
         new LinkedHashMap<>();

   private final Map<ImportBeanDefinitionRegistrar, AnnotationMetadata> importBeanDefinitionRegistrars =
         new LinkedHashMap<>();

   final Set<String> skippedBeanMethods = new HashSet<>();
    //...省略
}

上面几个属性，相信大家一看名字就大概猜到作用是什么了，我们接着往下看

7.ConfigurationClassParser.processConfigurationClass()

protected void processConfigurationClass(ConfigurationClass configClass, Predicate<String> filter) throws IOException {
   
   //...省略代码，主要处理合并、去重、过滤

   // Recursively process the configuration class and its superclass hierarchy.
   SourceClass sourceClass = asSourceClass(configClass, filter);
   do {
   
       //1.核心逻辑
      sourceClass = doProcessConfigurationClass(configClass, sourceClass, filter);
   }
   while (sourceClass != null);

   this.configurationClasses.put(configClass, configClass);
}

8.doProcessConfigurationClass()

protected final SourceClass doProcessConfigurationClass(
      ConfigurationClass configClass, SourceClass sourceClass, Predicate<String> filter)
      throws IOException {
   

   if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
   
      // Recursively process any member (nested) classes first
      processMemberClasses(configClass, sourceClass, filter);
   }

   // Process any @PropertySource annotations
   for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
         sourceClass.getMetadata(), PropertySources.class,
         org.springframework.context.annotation.PropertySource.class)) {
   
      if (this.environment instanceof ConfigurableEnvironment) {
   
         processPropertySource(propertySource);
      }
      else {
   
         logger.info("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
               "]. Reason: Environment must implement ConfigurableEnvironment");
      }
   }

   // Process any @ComponentScan annotations
   Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(
         sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);
   if (!componentScans.isEmpty() &&
         !this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {
   
      for (AnnotationAttributes componentScan : componentScans) {
   
         // The config class is annotated with @ComponentScan -> perform the scan immediately
         Set<BeanDefinitionHolder> scannedBeanDefinitions =
               this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
         // Check the set of scanned definitions for any further config classes and parse recursively if needed
         for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
   
            BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
            if (bdCand == null) {
   
               bdCand = holder.getBeanDefinition();
            }
            if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
   
               parse(bdCand.getBeanClassName(), holder.getBeanName());
            }
         }
      }
   }

   // Process any @Import annotations
   processImports(configClass, sourceClass, getImports(sourceClass), filter, true);

   // Process any @ImportResource annotations
   AnnotationAttributes importResource =
         AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
   if (importResource != null) {
   
      String[] resources = importResource.getStringArray("locations");
      Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");
      for (String resource : resources) {
   
         String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);
         configClass.addImportedResource(resolvedResource, readerClass);
      }
   }

   // Process individual @Bean methods
   Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
   for (MethodMetadata methodMetadata : beanMethods) {
   
      configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
   }

   // Process default methods on interfaces
   processInterfaces(configClass, sourceClass);

   // Process superclass, if any
   if (sourceClass.getMetadata().hasSuperClass()) {
   
      String superclass = sourceClass.getMetadata().getSuperClassName();
      if (superclass != null && !superclass.startsWith("java") &&
            !this.knownSuperclasses.containsKey(superclass)) {
   
         this.knownSuperclasses.put(superclass, configClass);
         // Superclass found, return its annotation metadata and recurse
         return sourceClass.getSuperClass();
      }
   }

   // No superclass -> processing is complete
   return null;
}

上面代码很长，但是spring已经做了英文注释了，这里就是实现了@PropertySource、@ComponentScan、@Import 、@ImportResource、@Bean，下面简单的解析一下

1、@PropertySource：读取文件，然后将值放到environment中

2、@ComponentScan/@ComponentScans：扫面路径，扫描到的如果有特殊注解@Service、@Conponent等就会创建Beandifinition然后注册

3、@Import：分下面几种

​ (1)实现了ImportSelector，会调用其selectImports，然后递归…，注册

​ (2)实现了ImportBeanDefinitionRegistrar，反射实例化，然后加入到ConfigClass中

4、@ImportResource：加入到configClass中

5、@Bean：就是解析被@Configuration注释的类（MainConfig）中的@Bean标注的方法，解析出来，然后放到ConfigClass的beanMethods属性中

到这里，就算简单的把配置类的资源都算解析完了。我们回到ConfigurationClassPostProcessor#processConfigBeanDefinitions中，注释2已经解析完了，我们接着看注释3

9.ConfigurationClassPostProcessor.loadBeanDefinitions()

public void loadBeanDefinitions(Set<ConfigurationClass> configurationModel) {
   
   TrackedConditionEvaluator trackedConditionEvaluator = new TrackedConditionEvaluator();
   for (ConfigurationClass configClass : configurationModel) {
   
      loadBeanDefinitionsForConfigurationClass(configClass, trackedConditionEvaluator);
   }
}

这个参数就是去解析后的所有的ConfigurationClass，我们注释2中解析的内容就是封装到这里面的，我们去看看它如何创建BeanDefinition

10.loadBeanDefinitionsForConfigurationClass

private void loadBeanDefinitionsForConfigurationClass(
      ConfigurationClass configClass, TrackedConditionEvaluator trackedConditionEvaluator) {
   

   if (trackedConditionEvaluator.shouldSkip(configClass)) {
   
      String beanName = configClass.getBeanName();
      if (StringUtils.hasLength(beanName) && this.registry.containsBeanDefinition(beanName)) {
   
         this.registry.removeBeanDefinition(beanName);
      }
      this.importRegistry.removeImportingClass(configClass.getMetadata().getClassName());
      return;
   }

    //1.注册@Import
   if (configClass.isImported()) {
   
      registerBeanDefinitionForImportedConfigurationClass(configClass);
   }
    //2.注册@Bean
   for (BeanMethod beanMethod : configClass.getBeanMethods()) {
   
      loadBeanDefinitionsForBeanMethod(beanMethod);
   }

    //3.解析ImportResources
   loadBeanDefinitionsFromImportedResources(configClass.getImportedResources());
   //4.注册ImportBeanDefinitionRegistrar
    loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());
}

这几个方法不难，大家可以自行阅读，这里提一下注册@Bean有两点需要注意

（1）bean如果没有名字，会以方法名作为bean的name

（2）通过@Bean注释的方法创建bean，其实是通过factoryMethodName调用的，大家可以去看注释2，和最后创建bean的代码AbstractAutowireCapableBeanFactory#createBeanInstance

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
   
   //...省略

    //重点看这里
   if (mbd.getFactoryMethodName() != null) {
   
      return instantiateUsingFactoryMethod(beanName, mbd, args);
   }

 //...省略

   // Candidate constructors for autowiring?
   Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
   if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
         mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
   
      return autowireConstructor(beanName, mbd, ctors, args);
   }

   // Preferred constructors for default construction?
   ctors = mbd.getPreferredConstructors();
   if (ctors != null) {
   
      return autowireConstructor(beanName, mbd, ctors, null);
   }

   // No special handling: simply use no-arg constructor.
   return instantiateBean(beanName, mbd);
}

感兴趣的可以自行研究吧，spring的源码还是非常庞大，需要一点点啃，共勉，加油！！！