interface that loggers should implement so that the stack can log to various loggers impl such as log4j, commons logging, sl4j, ..

封装的日志类，非常标准和实用，不限平台，通用日志接口，大型项目都在使用，很值得学习-Package log type, very standard and practical, not limited to the platform, commons logging, large-scale projects are in use, it is worth learning