npoi的使用方法

　　　　　private static MemoryStream RenderToExcel(DataTable dt)
        {
            if (Equals(dt, null))
            {
                return null;
            }

            MemoryStream ms = new MemoryStream();
            using (dt)
            {
                IWorkbook workbook = new HSSFWorkbook();
                ISheet sheet = workbook.CreateSheet();
                IRow headerRow = sheet.CreateRow(0);
                foreach (DataColumn column in dt.Columns)
                {
                    headerRow.CreateCell(column.Ordinal).SetCellValue(column.Caption);
                }
               
                int rowIndex = 1;
                foreach (DataRow row in dt.Rows)
                {
                    IRow dataRow = sheet.CreateRow(rowIndex);

                    foreach (DataColumn column in dt.Columns)
                    {
                        dataRow.CreateCell(column.Ordinal).SetCellValue(row[column.Caption].ToString());
                    }
                    rowIndex++;
                }

                workbook.Write(ms);
                ms.Flush();
                ms.Position = 0;

            }

            return ms;
        }

        private static void SaveToFile(MemoryStream ms, string dirPath, string fileName)
        {
            if (string.IsNullOrEmpty(dirPath) || string.IsNullOrEmpty(fileName))
            {
                return;
            }

            if (!Directory.Exists(dirPath))
            {
                Directory.CreateDirectory(dirPath);
            }

            using (FileStream fs = new FileStream(string.Format("{0}{1}", dirPath, fileName), FileMode.Create))
            {
                byte[] data = ms.ToArray();
                fs.Write(data, 0, data.Length);
                fs.Flush();

                data = null;
            }
        }

　　　　 public static void SaveExcel(DataTable dt, string dirPath, string fileName)
        {
            SaveToFile(RenderToExcel(dt), dirPath, fileName);
        }