static string ReadExcel()
        {
            DataTable dtTable = new DataTable();
            List<string> rowList = new List<string>();
            ISheet sheet;
            using (var stream = new FileStream("TestData.xlsx", FileMode.Open))
            {
                stream.Position = 0;
                XSSFWorkbook xssWorkbook = new XSSFWorkbook(stream);
                sheet = xssWorkbook.GetSheetAt(0);
                IRow headerRow = sheet.GetRow(0);
                int cellCount = headerRow.LastCellNum;
                for (int j = 0; j < cellCount; j++)
                {
                    ICell cell = headerRow.GetCell(j);
                    if (cell == null || string.IsNullOrWhiteSpace(cell.ToString())) continue;
                    {
                        dtTable.Columns.Add(cell.ToString());
                    } 
                }
                for (int i = (sheet.FirstRowNum + 1); i <= sheet.LastRowNum; i++)
                {
                    IRow row = sheet.GetRow(i);
                    if (row == null) continue;
                    if (row.Cells.All(d => d.CellType == CellType.Blank)) continue;
                    for (int j = row.FirstCellNum; j < cellCount; j++)
                    {
                        if (row.GetCell(j) != null)
                        {
                            if (!string.IsNullOrEmpty(row.GetCell(j).ToString()) && !string.IsNullOrWhiteSpace(row.GetCell(j).ToString()))
                            {
                                rowList.Add(row.GetCell(j).ToString());
                            }
                        }
                    }
                    if(rowList.Count>0)
                    dtTable.Rows.Add(rowList.ToArray());
                    rowList.Clear(); 
                }
            }
            return JsonConvert.SerializeObject(dtTable);
        }

static void WriteExcel()
        {
            List<UserDetails> persons = new List<UserDetails>()
            {
                new UserDetails() {ID="1001", Name="ABCD", City ="City1", Country="USA"},
                new UserDetails() {ID="1002", Name="PQRS", City ="City2", Country="INDIA"},
                new UserDetails() {ID="1003", Name="XYZZ", City ="City3", Country="CHINA"},
                new UserDetails() {ID="1004", Name="LMNO", City ="City4", Country="UK"},
           };

            // Lets converts our object data to Datatable for a simplified logic.
            // Datatable is most easy way to deal with complex datatypes for easy reading and formatting.

            DataTable table = (DataTable)JsonConvert.DeserializeObject(JsonConvert.SerializeObject(persons), (typeof(DataTable)));
            var memoryStream = new MemoryStream();
             
            using (var fs = new FileStream("Result.xlsx", FileMode.Create, FileAccess.Write))
            {
                IWorkbook workbook = new XSSFWorkbook();
                ISheet excelSheet = workbook.CreateSheet("Sheet1");

                List<String> columns = new List<string>();
                IRow row = excelSheet.CreateRow(0);
                int columnIndex = 0;
               
                foreach (System.Data.DataColumn column in table.Columns)
                {
                    columns.Add(column.ColumnName);
                    row.CreateCell(columnIndex).SetCellValue(column.ColumnName);
                    columnIndex++;
                }

                int rowIndex = 1;
                foreach (DataRow dsrow in table.Rows)
                {
                    row = excelSheet.CreateRow(rowIndex);
                    int cellIndex = 0;
                    foreach (String col in columns)
                    {
                        row.CreateCell(cellIndex).SetCellValue(dsrow[col].ToString());
                        cellIndex++;
                    }

                    rowIndex++;
                }
                workbook.Write(fs);
            }

        }