调试的时候IO异常指向 using (IWorkbook workbook = new HSSFWorkbook(excelFileStream)) 报错Invalid header signature; Read 32088581144510207, expected -2226271756974174256
说明这不是一个excel文件，导入csv不用npoi，npoi只能打开excel格式
读取csv:
http://www.cnblogs.com/Clin/archive/2013/03/14/2959022.html