@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
   String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
   Class<?>[] exclude() default {};
   String[] excludeName() default {};
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(AutoConfigurationPackages.Registrar.class)
public @interface AutoConfigurationPackage {
}

static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {
   @Override
   public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
       //注册
      register(registry, new PackageImport(metadata).getPackageName());
   }
	//这个方法没有地方调用，暂不分析
   @Override
   public Set<Object> determineImports(AnnotationMetadata metadata) {
      return Collections.singleton(new PackageImport(metadata));
   }
}

private final String packageName;
PackageImport(AnnotationMetadata metadata) {
   this.packageName = ClassUtils.getPackageName(metadata.getClassName());
}

public static String getPackageName(String fqClassName) {
   Assert.notNull(fqClassName, "Class name must not be null");
   int lastDotIndex = fqClassName.lastIndexOf(PACKAGE_SEPARATOR);
   return (lastDotIndex != -1 ? fqClassName.substring(0, lastDotIndex) : "");
}

String getPackageName() {
   return this.packageName;
}

private static final String BEAN = AutoConfigurationPackages.class.getName();
public static void register(BeanDefinitionRegistry registry, String... packageNames) {
    //已经注册过 BEAN 了，代表不是第一次调用AutoConfigurationPackages.Registrar
   if (registry.containsBeanDefinition(BEAN)) {
      BeanDefinition beanDefinition = registry.getBeanDefinition(BEAN);
      ConstructorArgumentValues constructorArguments = beanDefinition.getConstructorArgumentValues();
       //将这次调用AutoConfigurationPackages.Registrar，将标注@AutoConfigurationPackage 注解的类的包名添加到 BEAN 的参数中
      constructorArguments.addIndexedArgumentValue(0, addBasePackages(constructorArguments, packageNames));
   }
   else {
       //第一次调用AutoConfigurationPackages.Registrar，注册 BEAN
      GenericBeanDefinition beanDefinition = new GenericBeanDefinition();
      beanDefinition.setBeanClass(BasePackages.class);
       //获取BasePackages构造器的参数，是个 String... ，将packageNames放到数组第一个位置
      beanDefinition.getConstructorArgumentValues().addIndexedArgumentValue(0, packageNames);
      beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
      registry.registerBeanDefinition(BEAN, beanDefinition);
   }
}

static final class BasePackages {
   private final List<String> packages;
   private boolean loggedBasePackageInfo;
   BasePackages(String... names) {
      List<String> packages = new ArrayList<>();
      for (String name : names) {
         if (StringUtils.hasText(name)) {
            packages.add(name);
         }
      }
      this.packages = packages;
   }
   List<String> get() {
      if (!this.loggedBasePackageInfo) {
         if (this.packages.isEmpty()) {
            if (logger.isWarnEnabled()) {
				...//只是输出日志
            }
         }
         else {
            if (logger.isDebugEnabled()) {
               String packageNames = StringUtils.collectionToCommaDelimitedString(this.packages);
               ...//输出日志
            }
         }
         this.loggedBasePackageInfo = true;
      }
      return this.packages;
   }
}

private static String[] addBasePackages(ConstructorArgumentValues constructorArguments, String[] packageNames) {
    //取出BasePackages构造器的参数 String... 
   String[] existing = (String[]) constructorArguments.getIndexedArgumentValue(0, String[].class).getValue();
    //创建新的集合，将原有的包名和现有的包名添加进去，用set去重，然后返回
   Set<String> merged = new LinkedHashSet<>();
   merged.addAll(Arrays.asList(existing));
   merged.addAll(Arrays.asList(packageNames));
   return StringUtils.toStringArray(merged);
}

public String[] selectImports(AnnotationMetadata annotationMetadata) {
    //不起用自动装配
   if (!isEnabled(annotationMetadata)) {
      return NO_IMPORTS;
   }
    //获得AutoConfiguration的注解元数据
   AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
         .loadMetadata(this.beanClassLoader);
   AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(autoConfigurationMetadata,
         annotationMetadata);
   return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
}

protected AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata,
      AnnotationMetadata annotationMetadata) {
   if (!isEnabled(annotationMetadata)) {
      return EMPTY_ENTRY;
   }
    //获取注解的属性
   AnnotationAttributes attributes = getAttributes(annotationMetadata);
    //获取实现EnableAutoConfiguration的类名集合
   List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
    //去重
   configurations = removeDuplicates(configurations);
    //获取要排除的类名
   Set<String> exclusions = getExclusions(annotationMetadata, attributes);
   checkExcludedClasses(configurations, exclusions);
    //排除
   configurations.removeAll(exclusions);
    //过滤
   configurations = filter(configurations, autoConfigurationMetadata);
   fireAutoConfigurationImportEvents(configurations, exclusions);
   return new AutoConfigurationEntry(configurations, exclusions);
}

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
    //利用spi获取实现了EnableAutoConfiguration的类名集合
   List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),
         getBeanClassLoader());
   Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you "
         + "are using a custom packaging, make sure that file is correct.");
   return configurations;
}

protected Class<?> getSpringFactoriesLoaderFactoryClass() {
   return EnableAutoConfiguration.class;
}

protected final <T> List<T> removeDuplicates(List<T> list) {
   return new ArrayList<>(new LinkedHashSet<>(list));
}

protected Set<String> getExclusions(AnnotationMetadata metadata, AnnotationAttributes attributes) {
   Set<String> excluded = new LinkedHashSet<>();
   excluded.addAll(asList(attributes, "exclude"));
   excluded.addAll(Arrays.asList(attributes.getStringArray("excludeName")));
   excluded.addAll(getExcludeAutoConfigurationsProperty());
   return excluded;
}

private List<String> getExcludeAutoConfigurationsProperty() {
   if (getEnvironment() instanceof ConfigurableEnvironment) {
      Binder binder = Binder.get(getEnvironment());
      return binder.bind(PROPERTY_NAME_AUTOCONFIGURE_EXCLUDE, String[].class).map(Arrays::asList)
            .orElse(Collections.emptyList());
   }
   String[] excludes = getEnvironment().getProperty(PROPERTY_NAME_AUTOCONFIGURE_EXCLUDE, String[].class);
   return (excludes != null) ? Arrays.asList(excludes) : Collections.emptyList();
}

private List<String> filter(List<String> configurations, AutoConfigurationMetadata autoConfigurationMetadata) {
   long startTime = System.nanoTime();
   String[] candidates = StringUtils.toStringArray(configurations);
   boolean[] skip = new boolean[candidates.length];
   boolean skipped = false;
   for (AutoConfigurationImportFilter filter : getAutoConfigurationImportFilters()) {
      invokeAwareMethods(filter);
      boolean[] match = filter.match(candidates, autoConfigurationMetadata);
      for (int i = 0; i < match.length; i++) {
         if (!match[i]) {
            skip[i] = true;
            candidates[i] = null;
            skipped = true;
         }
      }
   }
   if (!skipped) {
      return configurations;
   }
   List<String> result = new ArrayList<>(candidates.length);
   for (int i = 0; i < candidates.length; i++) {
      if (!skip[i]) {
         result.add(candidates[i]);
      }
   }
   if (logger.isTraceEnabled()) {
      int numberFiltered = configurations.size() - result.size();
      logger.trace("Filtered " + numberFiltered + " auto configuration class in "
            + TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startTime) + " ms");
   }
   return new ArrayList<>(result);
}

protected List<AutoConfigurationImportFilter> getAutoConfigurationImportFilters() {
   return SpringFactoriesLoader.loadFactories(AutoConfigurationImportFilter.class, this.beanClassLoader);
}