ASP .NET 导入导出EXCEL(NPOI)

1.兼容 excel2003版 或excel2007+版  

using NPOI.HSSF.UserModel;
using NPOI.SS.UserModel;
using NPOI.XSSF.UserModel;
using System;
using System.Collections.Generic;
using System.Data;
using System.IO;

namespace WindowsFormsApplicationExcel
{
    public static class NPOIExcelHelper
    {
        /// <summary>
        /// Excel导入成Datable
        /// </summary>
        /// <param name="file">导入路径(包含文件名与扩展名)</param>
        /// <returns></returns>
        public static DataTable ExcelToTable(string file)
        {
            try
            {
                DataTable dt = new DataTable();
                IWorkbook workbook;
                string fileExt = Path.GetExtension(file).ToLower();
                using (FileStream fs = new FileStream(file, FileMode.Open, FileAccess.Read))
                {
                    //XSSFWorkbook 适用XLSX格式，HSSFWorkbook 适用XLS格式
                    if (fileExt == ".xlsx") { workbook = new XSSFWorkbook(fs); } else if (fileExt == ".xls") { workbook = new HSSFWorkbook(fs); } else { workbook = null; }
                    if (workbook == null) { return null; }
                    ISheet sheet = workbook.GetSheetAt(0);

                    //表头  
                    IRow header = sheet.GetRow(sheet.FirstRowNum);
                    List<int> columns = new List<int>();
                    for (int i = 0; i < header.LastCellNum; i++)
                    {
                        object obj = GetValueType(header.GetCell(i));
                        if (obj == null || obj.ToString() == string.Empty)
                        {
                            dt.Columns.Add(new DataColumn("Columns" + i.ToString()));
                        }
                        else
                            dt.Columns.Add(new DataColumn(obj.ToString()));
                        columns.Add(i);
                    } 
                    //数据  
                    for (int i = sheet.FirstRowNum + 1; i <= sheet.LastRowNum; i++)
                    {
                        DataRow dr = dt.NewRow();
                        bool hasValue = false;
                        foreach (int j in columns)
                        {
                            dr[j] = GetValueType(sheet.GetRow(i).GetCell(j));
                            if (dr[j] != null && dr[j].ToString() != string.Empty)
                            {
                                hasValue = true;
                            }
                        }
                        if (hasValue)
                        {
                            dt.Rows.Add(dr);
                        }
                    }
                }
                return dt;
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

        /// <summary>
        /// Datable导出成Excel
        /// </summary>
        /// <param name="dt"></param>
        /// <param name="file">导出路径(包括文件名与扩展名)</param>
        public static MemoryStream TableToExcel(DataTable dt, string file)
        {
            try
            {
                IWorkbook workbook;
                string fileExt = Path.GetExtension(file).ToLower();
                if (fileExt == ".xlsx") { workbook = new XSSFWorkbook(); } else if (fileExt == ".xls") { workbook = new HSSFWorkbook(); } else { workbook = null; }
                if (workbook == null) { return null; }
                ISheet sheet = string.IsNullOrEmpty(dt.TableName) ? workbook.CreateSheet("Sheet1") : workbook.CreateSheet(dt.TableName);

                //表头  
                IRow row = sheet.CreateRow(0);
                for (int i = 0; i < dt.Columns.Count; i++)
                {
                    ICell cell = row.CreateCell(i);
                    cell.SetCellValue(dt.Columns[i].ColumnName);
                }
                ////表头  
                //IRow row = sheet.CreateRow(0);
                //string[] ColumnName = { "列名1", "列名2", "列名3", "列名4" };
                //for (int i = 0; i < dt.Columns.Count; i++)
                //{
                //    ICell cell = row.CreateCell(i);
                //    foreach (var item in ColumnName)
                //    {
                //        cell.SetCellValue(item);
                //    } 
                //}
                //数据  
                for (int i = 0; i < dt.Rows.Count; i++)
                {
                    IRow row1 = sheet.CreateRow(i + 1);
                    for (int j = 0; j < dt.Columns.Count; j++)
                    {
                        ICell cell = row1.CreateCell(j);
                        cell.SetCellValue(dt.Rows[i][j].ToString());
                    }
                }

                //转为字节数组  
                using (MemoryStream stream = new MemoryStream())
                {
                    workbook.Write(stream);
                    stream.Flush();

                    return stream; 
                }  
            }
            catch (Exception ex)
            {
                throw ex;
            }
        } 

        //获取单元格值
        private static object GetValueType(ICell cell)
        {
            if (cell == null)
                return null;
            switch (cell.CellType)
            {
                case CellType.Blank: //BLANK:  
                    return null;
                case CellType.Boolean: //BOOLEAN:  
                    return cell.BooleanCellValue;
                case CellType.Numeric: //NUMERIC:  
                    return cell.NumericCellValue;
                case CellType.String: //STRING:  
                    return cell.StringCellValue;
                case CellType.Error: //ERROR:  
                    return cell.ErrorCellValue;
                case CellType.Formula: //FORMULA:  
                default:
                    return "=" + cell.CellFormula;
            }
        }

    }

}