Spring AutowireCandidateResolver

public interface AutowireCandidateResolver {

	/**
	 * Determine whether the given bean definition qualifies as an
	 * autowire candidate for the given dependency.
	 * <p>The default implementation checks
	 * {@link org.springframework.beans.factory.config.BeanDefinition#isAutowireCandidate()}.
	 *
	 * 是否是自动注入的候选者
	 * @param bdHolder the bean definition including bean name and aliases
	 * @param descriptor the descriptor for the target method parameter or field
	 * @return whether the bean definition qualifies as autowire candidate
	 * @see org.springframework.beans.factory.config.BeanDefinition#isAutowireCandidate()
	 */
	default boolean isAutowireCandidate(BeanDefinitionHolder bdHolder, DependencyDescriptor descriptor) {
		return bdHolder.getBeanDefinition().isAutowireCandidate();
	}

	/**
	 * Determine whether the given descriptor is effectively required.
	 * <p>The default implementation checks {@link DependencyDescriptor#isRequired()}.
	 * 是否必须
	 * @param descriptor the descriptor for the target method parameter or field
	 * @return whether the descriptor is marked as required or possibly indicating
	 * non-required status some other way (e.g. through a parameter annotation)
	 * @since 5.0
	 * @see DependencyDescriptor#isRequired()
	 */
	default boolean isRequired(DependencyDescriptor descriptor) {
		return descriptor.isRequired();
	}

	/**
	 * Determine whether the given descriptor declares a qualifier beyond the type
	 * (typically - but not necessarily - a specific kind of annotation).
	 * <p>The default implementation returns {@code false}.
	 *
	 * 以来描述符是否存在对应的对象
	 * @param descriptor the descriptor for the target method parameter or field
	 * @return whether the descriptor declares a qualifier, narrowing the candidate
	 * status beyond the type match
	 * @since 5.1
	 * @see org.springframework.beans.factory.annotation.QualifierAnnotationAutowireCandidateResolver#hasQualifier
	 */
	default boolean hasQualifier(DependencyDescriptor descriptor) {
		return false;
	}

	/**
	 * Determine whether a default value is suggested for the given dependency.
	 * <p>The default implementation simply returns {@code null}.
	 *
	 * 获取数据(可能存在默认值)
	 * @param descriptor the descriptor for the target method parameter or field
	 * @return the value suggested (typically an expression String),
	 * or {@code null} if none found
	 * @since 3.0
	 */
	@Nullable
	default Object getSuggestedValue(DependencyDescriptor descriptor) {
		return null;
	}

	/**
	 * Build a proxy for lazy resolution of the actual dependency target,
	 * if demanded by the injection point.
	 * <p>The default implementation simply returns {@code null}.
	 *
	 * 延迟加载对象
	 * @param descriptor the descriptor for the target method parameter or field
	 * @param beanName the name of the bean that contains the injection point
	 * @return the lazy resolution proxy for the actual dependency target,
	 * or {@code null} if straight resolution is to be performed
	 * @since 4.0
	 */
	@Nullable
	default Object getLazyResolutionProxyIfNecessary(DependencyDescriptor descriptor, @Nullable String beanName) {
		return null;
	}

}