Log：日志工具输出log的使用

　　日志的简单使用，三种方式。

1. org.apache.commons.logging.Log

   //import org.apache.commons.logging.Log;
   //import org.apache.commons.logging.LogFactory;
   private static final Log log = LogFactory.getLog(xxxServiceImpl.class);
   
   log.info(Object msg);

2. log4j 1.x 版本：org.apache.log4j.Logger

   //org.apache.log4j.Logger;
   private final Logger logger = Logger.getLogger(this.getClass());
   
   logger.info(Object msg);

3. log4j 2.x 版本：org.apache.logging.log4j.Logger

   private static final Logger logger = LogManager.getLogger(xxxClass.class);
   
   logger.info(String msg);