Extension of the {@link BeanFactory} interface to be implemented by bean factories
* that can enumerate all their bean instances, rather than attempting bean lookup
* by name one by one as requested by clients. BeanFactory implementations that
* preload all their bean definitions (such as XML-based factories) may implement
* this interface.
ListableBeanFactory的接口如下:
通过接口可以获取BeanDefinition,BeanNames,Bean Instance, Bean Annotations等相关信息。