Spring中用烂了的@Component注解是怎么实现的呢？

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Indexed
public @interface Component {

 
 String value() default "";

}

protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
  Assert.notEmpty(basePackages, "At least one base package must be specified");
  Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
        // 遍历多个扫描目录，如本例中的com.alvinlkk
  for (String basePackage : basePackages) {
            // 核心方法查找所有符合条件的BeanDefinition, 该方法后面重点关注
   Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
   // 遍历找到的BeanDefinition
            for (BeanDefinition candidate : candidates) {
    ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
    candidate.setScope(scopeMetadata.getScopeName());
    String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
    if (candidate instanceof AbstractBeanDefinition) {
     postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
    }
    if (candidate instanceof AnnotatedBeanDefinition) {
     AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
    }
                // 验证BeanDefinition
    if (checkCandidate(beanName, candidate)) {
     BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
     definitionHolder =
       AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
     beanDefinitions.add(definitionHolder);
                    // 注册BeanDefinition到registry中
     registerBeanDefinition(definitionHolder, this.registry);
    }
   }
  }
  return beanDefinitions;
 }

public Set<BeanDefinition> findCandidateComponents(String basePackage) {
  // 判断组件是否加了索引，打包后默认会有索引，用于加快扫描
        if (this.componentsIndex != null && indexSupportsIncludeFilters()) {
   return addCandidateComponentsFromIndex(this.componentsIndex, basePackage);
  }
       // 重点查看else逻辑
  else {
   return scanCandidateComponents(basePackage);
  }
 }

private Set<BeanDefinition> scanCandidateComponents(String basePackage) {
  Set<BeanDefinition> candidates = new LinkedHashSet<>();
  try {
            // 解析出需要扫描的路径，本例是classpath*:com/alvinlkk*.class
   String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
     resolveBasePackage(basePackage) + '/' + this.resourcePattern;
   // 根据扫描路径找到所有的Resource
            Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);
   boolean traceEnabled = logger.isTraceEnabled();
   boolean debugEnabled = logger.isDebugEnabled();
            // 遍历扫描路径
   for (Resource resource : resources) {
    if (traceEnabled) {
     logger.trace("Scanning " + resource);
    }
    try {
                    // 解析出扫描到类的元数据信息，里面包含了注解信息
     MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource);
     // 关键方法，判断是否候选组件
                    if (isCandidateComponent(metadataReader)) {
      ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
      sbd.setSource(resource);
      if (isCandidateComponent(sbd)) {
       if (debugEnabled) {
        logger.debug("Identified candidate component class: " + resource);
       }
       candidates.add(sbd);
      }
      else {
       if (debugEnabled) {
        logger.debug("Ignored because not a concrete top-level class: " + resource);
       }
      }
     }
     else {
      if (traceEnabled) {
       logger.trace("Ignored because not matching any filter: " + resource);
      }
     }
    }
    catch (FileNotFoundException ex) {
     if (traceEnabled) {
      logger.trace("Ignored non-readable " + resource + ": " + ex.getMessage());
     }
    }
    catch (Throwable ex) {
     throw new BeanDefinitionStoreException(
       "Failed to read candidate component class: " + resource, ex);
    }
   }
  }
  catch (IOException ex) {
   throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);
  }
  return candidates;
 }

// 判断是否候选的Bean Component
protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {
  // exclude过滤器,在exclude过滤其中的，会直接排除掉，返回false
        for (TypeFilter tf : this.excludeFilters) {
   if (tf.match(metadataReader, getMetadataReaderFactory())) {
    return false;
   }
  }
       // include过滤器， 这里会看到有AnnotationTypeFilter,注解类型过滤器
  for (TypeFilter tf : this.includeFilters) {
            // 调用AnnotationTypeFilter的match方法，来判断是否满足条件
   if (tf.match(metadataReader, getMetadataReaderFactory())) {
                // 下面在进行Condition的判断，就是类上的@Conditional，这里不是重点
    return isConditionMatch(metadataReader);
   }
  }
  return false;
 }