NPOI2.0 ExcelToDataTable工具类分享。支持合并单元格数据处理

项目需要，重拾NPOI.不会组织语言，直接分享代码。

 public enum CellDataType
    {
        Date,
        Time,
        DateTime,
        String
    }

    public class ExcelHelper
    {

        /// <summary>    
        /// 由Excel导入DataTable    
        /// </summary>    
        /// <param name="excelStream">Excel文件流</param>   
        /// <param name="sheetName">Excel工作表</param>    
        /// <param name="sheetIndex">Excel工作表</param>    
        /// <param name="headerRowIndex">Excel表头行索引</param>    
        /// <returns>DataTable</returns>    
        private static DataTable ExcelToDataTable(Stream excelStream,string sheetName, int sheetIndex, int headerRowIndex)
        {
            IWorkbook workbook = WorkbookFactory.Create(excelStream);
            ISheet sheet = null;
            if (!string.IsNullOrEmpty(sheetName))
            {
                sheet = workbook.GetSheet(sheetName);
            }
            else
            {
                sheet = workbook.GetSheetAt(sheetIndex);
            }
            DataTable table = new DataTable();
            IRow headerRow = sheet.GetRow(headerRowIndex);
            int cellCount = headerRow.LastCellNum;
            for (int i = headerRow.FirstCellNum; i < cellCount; i++)
            {
                DataColumn column = new DataColumn(headerRow.GetCell(i).ToString());
                table.Columns.Add(column);
            }
            for (int i = (sheet.FirstRowNum + 1); i <= sheet.LastRowNum; i++)
            {
                IRow row = sheet.GetRow(i);
                DataRow dataRow = table.NewRow();
                for (int j = row.FirstCellNum; j < cellCount; j++)
                {
                    ICell cell = row.GetCell(j);
                    dataRow[j] = GetText(cell);
                }
                table.Rows.Add(dataRow);
            }

            #region 处理合并单元格

            int ij = sheet.NumMergedRegions;

            for (int i = 0; i < ij; i++)
            {
                CellRangeAddress r = sheet.GetMergedRegion(i);
                if (r.FirstRow <= headerRowIndex)
                    continue;
                object o = table.Rows[r.FirstRow - (headerRowIndex + 1)][r.FirstColumn];
                for (int jr = r.FirstRow; jr <= r.LastRow; jr++)
                {
                    if ((jr - (headerRowIndex + 1)) < table.Rows.Count)//处理合并列大于数据总列时这种不规范的EXCEL文本，
                    {
                        for (int jc = r.FirstColumn; jc <= r.LastColumn; jc++)
                        {
                            table.Rows[jr - (headerRowIndex + 1)][jc] = o;
                        }
                    }
                }

            }

            #endregion
            excelStream.Close();
            workbook = null;
            sheet = null;
            return table;
        }

        /// <summary>    
        /// 由Excel导入DataTable   
        /// </summary>   
        ///  <param name="excelFilePath">Excel文件路径，为物理路径。</param>   
        /// <param name="sheetName">Excel工作表名称</param>    
        /// <param name="headerRowIndex">Excel表头行索引</param>    
        /// <returns>DataTable</returns>    
        public static DataTable ExcelToDataTable(string excelFilePath, string sheetName, int headerRowIndex)
        {
            using (FileStream stream = System.IO.File.OpenRead(excelFilePath))
            {
                return ExcelToDataTable(stream, sheetName,-1, headerRowIndex);
            }
        }

        /// <summary>    
        /// 由Excel导入DataTable    
        /// </summary>    
        /// <param name="excelFilePath">Excel文件路径，为物理路径。</param>    
        /// <param name="sheetName">Excel工作表索引</param>    
        /// <param name="headerRowIndex">Excel表头行索引</param>    
        /// <returns>DataTable</returns>    
        public static DataTable ExcelToDataTable(string excelFilePath, int sheetIndex, int headerRowIndex)
        {
            using (FileStream stream = System.IO.File.OpenRead(excelFilePath))
            {
                return ExcelToDataTable(stream,null, sheetIndex, headerRowIndex);
            }
        }


        private static CellDataType GetCellDataType(ICell cell)
        {
            string dataFormatString = cell.CellStyle.GetDataFormatString();

            if (dataFormatString.ToLower().IndexOf("y") != -1 && dataFormatString.ToLower().IndexOf("h") != -1)
            {
                return CellDataType.DateTime;
            }
            else if (dataFormatString.ToLower().IndexOf("y") != -1 && dataFormatString.ToLower().IndexOf("h") == -1)
            {
                return CellDataType.Date;
            }
            else if (dataFormatString.ToLower().IndexOf("y") == -1 && dataFormatString.ToLower().IndexOf("h") != -1)
            {
                return CellDataType.Time;
            }
            else
            {
                return CellDataType.String;
            }
        }

        private static string GetText(ICell cell)
        {
            if (cell == null)
            {
                return "";
            }

            string value = null;
            switch (cell.CellType)
            {
                case CellType.ERROR:
                    value = ErrorEval.GetText(cell.ErrorCellValue);
                    break;
                case CellType.FORMULA:
                    value = GetFormulaText(cell);
                    break;
                case CellType.NUMERIC:
                    CellDataType cdt = GetCellDataType(cell);
                    if (cdt == CellDataType.DateTime)
                    {
                        value = cell.DateCellValue.ToString("yyyy-MM-dd HH:mm:ss");
                    }
                    else if (cdt == CellDataType.Date)
                    {
                        value = cell.DateCellValue.ToString("yyyy-MM-dd");
                    }
                    else if (cdt == CellDataType.Time)
                    {
                        value = cell.DateCellValue.ToString("HH:mm:ss");
                    }
                    else
                    {
                        value = cell.NumericCellValue.ToString();
                    }
                    break;
                case CellType.STRING:
                    value = cell.StringCellValue;
                    break;
                default:
                    value = cell.ToString();
                    break;
            }
            return value;
        }

        private static string GetFormulaText(ICell cell)
        {
            string value = null;
            switch (cell.CachedFormulaResultType)
            {
                case CellType.ERROR:
                    value = ErrorEval.GetText(cell.ErrorCellValue);
                    break;
                case CellType.NUMERIC:
                    value = cell.NumericCellValue.ToString();
                    break;
                case CellType.STRING:
                    value = cell.StringCellValue;
                    break;
                default:
                    value = cell.ToString();
                    break;
            }
            return value;
        }