说明：  DBUtils提供了一个接口ResultSetHandler，它就是用来ResultSet转换成目标类型的工具。你可以自己去实现这个接口，把ResultSet转换成你想要的类型。 DBUtils提供了很多个ResultSetHandler接口的实现，这些实现已经基本够用了，我们通常不用自己去实现ResultSet接口了
(DBUtils provides an interface ResultSetHandler, which is a tool used to convert ResultSet into a target type. You can implement this interface by yourself and convert the ResultSet into the type you want. DBUtils provides many implementations of ResultSetHandler interfaces that are basically enough, and we usually do not have to implement the ResultSet interface ourselves)