poi在java中可用，在web项目中不可用

 Servlet.service() for servlet [servlets.Upload] in context with path [/Excel] threw exception [Servlet execution threw an exception] with root cause

java.lang.ClassNotFoundException: org.apache.poi.xssf.usermodel.XSSFWorkbook

 在main函数里面和web里面不太一样

web要到web-info底下的lib目录查找 jar