POI组件的详细介绍文档：
https://www.cnblogs.com/huajiezh/p/5467821.html
.xls 对应 HSSFWorkbook book=new HSSFWorkbook(io);
<dependency>
<groupId>org.apache.poi</groupId>
<artifactId>poi</artifactId>
<version>3.17</version>
</dependency>
.xlsx 对应 XSSFWorkbook book=new XSSFWorkbook(io)）
<dependency>
<groupId>org.apache.poi</groupId>
<artifactId>poi-ooxml</artifactId>
<version>3.17</version>
</dependency>
原文：https://www.cnblogs.com/domi22/p/9742839.html