Spring Import

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

    /**
     * {@link Configuration @Configuration}, {@link ImportSelector},
     * {@link ImportBeanDefinitionRegistrar}, or regular component classes to import.
     *
     * 需要导入的类
     */
    Class<?>[] value();
}

public interface ImportBeanDefinitionRegistrar {

    /**
     * Register bean definitions as necessary based on the given annotation metadata of
     * the importing {@code @Configuration} class.
     * <p>Note that {@link BeanDefinitionRegistryPostProcessor} types may <em>not</em> be
     * registered here, due to lifecycle constraints related to {@code @Configuration}
     * class processing.
     *
     * 对import value属性的注册
     * @param importingClassMetadata annotation metadata of the importing class
     * @param registry               current bean definition registry
     */
    void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry);

}

public class AutoProxyRegistrar implements ImportBeanDefinitionRegistrar {

    private final Log logger = LogFactory.getLog(getClass());

    /**
     * 注册import bean定义
     */
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        boolean candidateFound = false;
        // 获取注解
        Set<String> annTypes = importingClassMetadata.getAnnotationTypes();
        for (String annType : annTypes) {
            // 注解属性
            AnnotationAttributes candidate = AnnotationConfigUtils.attributesFor(importingClassMetadata, annType);
            if (candidate == null) {
                continue;
            }
            // 获取 mode 属性
            Object mode = candidate.get("mode");
            // 获取代理对象
            Object proxyTargetClass = candidate.get("proxyTargetClass");
            if (mode != null && proxyTargetClass != null && AdviceMode.class == mode.getClass() &&
                    Boolean.class == proxyTargetClass.getClass()) {
                candidateFound = true;
                if (mode == AdviceMode.PROXY) {
                    // 注册
                    AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
                    if ((Boolean) proxyTargetClass) {
                        AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
                        return;
                    }
                }
            }
        }
        if (!candidateFound && logger.isInfoEnabled()) {
            String name = getClass().getSimpleName();
            logger.info(String.format("%s was imported but no annotations were found " +
                    "having both 'mode' and 'proxyTargetClass' attributes of type " +
                    "AdviceMode and boolean respectively. This means that auto proxy " +
                    "creator registration and configuration may not have occurred as " +
                    "intended, and components may not be proxied as expected. Check to " +
                    "ensure that %s has been @Import'ed on the same class where these " +
                    "annotations are declared; otherwise remove the import of %s " +
                    "altogether.", name, name, name));
        }
    }

}