@Configuration(proxyBeanMethods = false)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@ConditionalOnClass(ServletRequest.class)
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(ServerProperties.class)
@Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
    ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
    ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
    ServletWebServerFactoryConfiguration.EmbeddedUndertow.class })
public class ServletWebServerFactoryAutoConfiguration {

  // ...
  
  /**
   * Registers a {@link WebServerFactoryCustomizerBeanPostProcessor}. Registered via
   * {@link ImportBeanDefinitionRegistrar} for early registration.
   */
  public static class BeanPostProcessorsRegistrar implements ImportBeanDefinitionRegistrar, BeanFactoryAware {

    private ConfigurableListableBeanFactory beanFactory;

    // 實(shí)現(xiàn)BeanFactoryAware的方法，設(shè)置BeanFactory
    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
      if (beanFactory instanceof ConfigurableListableBeanFactory) {
        this.beanFactory = (ConfigurableListableBeanFactory) beanFactory;
      }
    }

    // 注冊(cè)一個(gè)WebServerFactoryCustomizerBeanPostProcessor
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
        BeanDefinitionRegistry registry) {
      if (this.beanFactory == null) {
        return;
      }
      registerSyntheticBeanIfMissing(registry, "webServerFactoryCustomizerBeanPostProcessor",
          WebServerFactoryCustomizerBeanPostProcessor.class);
      registerSyntheticBeanIfMissing(registry, "errorPageRegistrarBeanPostProcessor",
          ErrorPageRegistrarBeanPostProcessor.class);
    }

    // 檢查并注冊(cè)Bean
    private void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry, String name, Class<?> beanClass) {
      // 檢查指定類型的Bean name數(shù)組是否存在，如果不存在則創(chuàng)建Bean并注入到容器中
      if (ObjectUtils.isEmpty(this.beanFactory.getBeanNamesForType(beanClass, true, false))) {
        RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass);
        beanDefinition.setSynthetic(true);
        registry.registerBeanDefinition(name, beanDefinition);
      }
    }
  }

@Documented
@Inherited
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER})
public @interface Mapper {
}

@Mapper
public class UserMapper {
}

public class MapperAutoConfigureRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware {
  
  private ResourceLoader resourceLoader;

  @Override
  public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
    MapperBeanDefinitionScanner scanner = new MapperBeanDefinitionScanner(registry, false);
    scanner.setResourceLoader(resourceLoader);
    scanner.registerFilters();
    scanner.addIncludeFilter(new AnnotationTypeFilter(Mapper.class));
    scanner.doScan("com.secbro2.learn.mapper");
  }

  @Override
  public void setResourceLoader(ResourceLoader resourceLoader) {
    this.resourceLoader = resourceLoader;
  }
}

public class MapperBeanDefinitionScanner extends ClassPathBeanDefinitionScanner {

  public MapperBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters) {
    super(registry, useDefaultFilters);
  }

  protected void registerFilters() {
    addIncludeFilter(new AnnotationTypeFilter(Mapper.class));
  }

  @Override
  protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
    return super.doScan(basePackages);
  }
}

@Configuration
@Import(MapperAutoConfigureRegistrar.class)
public class MapperAutoConfig {
}

@RunWith(SpringRunner.class)
@SpringBootTest
public class MapperAutoConfigureRegistrarTest {

  @Autowired
  UserMapper userMapper;

  @Test
  public void contextLoads() {
    System.out.println(userMapper.getClass());
  }
}