导出Excel（npoi）

public static void ExportExcel(DataTable dt, string fileName = "")
{
//生成Excel
IWorkbook book = BuildWorkbook(dt);

//web 下载
if (fileName == "")
fileName = string.Format("{0:yyyyMMddHHmmssffff}", DateTime.Now);
fileName = fileName.Trim();
string ext = Path.GetExtension(fileName);

if (ext.ToLower() == ".xls" || ext.ToLower() == ".xlsx")
fileName = fileName.Replace(ext, string.Empty);

HttpResponse httpResponse = HttpContext.Current.Response;
httpResponse.Clear();
httpResponse.Buffer = true;
httpResponse.Charset = Encoding.UTF8.BodyName;
httpResponse.AppendHeader("Content-Disposition", "attachment;filename=" + fileName + ".xls");
httpResponse.ContentEncoding = Encoding.UTF8;
httpResponse.ContentType = "application/vnd.ms-excel; charset=UTF-8";
book.Write(httpResponse.OutputStream);
httpResponse.End();
}