C#通过NPOI操作Excel的实例代码

public class ExcelHelper
  {
    /// <summary>
    /// 根据Excel和Sheet返回DataTable
    /// </summary>
    /// <param name="filePath">Excel文件地址</param>
    /// <param name="sheetIndex">Sheet索引</param>
    /// <returns>DataTable</returns>
    public static DataTable GetDataTable(string filePath, int sheetIndex)
    {
      return GetDataSet(filePath, sheetIndex).Tables[0];
    }

    /// <summary>
    /// 根据Excel返回DataSet
    /// </summary>
    /// <param name="filePath">Excel文件地址</param>
    /// <param name="sheetIndex">Sheet索引，可选，默认返回所有Sheet</param>
    /// <returns>DataSet</returns>
    public static DataSet GetDataSet(string filePath, int? sheetIndex = null)
    {
      DataSet ds = new DataSet();
      IWorkbook fileWorkbook;
      using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read))
      {
        if (filePath.Last() == 's')
        {
          try
          {
            fileWorkbook = new HSSFWorkbook(fs);
          }
          catch (Exception ex)
          {
            throw ex;
          }
        }
        else
        {
          try
          {
            fileWorkbook = new XSSFWorkbook(fs);
          }
          catch
          {
            fileWorkbook = new HSSFWorkbook(fs);
          }
        }
      }

      for (int i = 0; i < fileWorkbook.NumberOfSheets; i++)
      {
        if (sheetIndex != null && sheetIndex != i)
          continue;
        DataTable dt = new DataTable();
        ISheet sheet = fileWorkbook.GetSheetAt(i);

        //表头
        IRow header = sheet.GetRow(sheet.FirstRowNum);
        List<int> columns = new List<int>();
        for (int j = 0; j < header.LastCellNum; j++)
        {
          object obj = GetValueTypeForXLS(header.GetCell(j) as HSSFCell);
          if (obj == null || obj.ToString() == string.Empty)
          {
            dt.Columns.Add(new DataColumn("Columns" + j.ToString()));
          }
          else
            dt.Columns.Add(new DataColumn(obj.ToString()));
          columns.Add(j);
        }
        //数据
        IEnumerator rows = sheet.GetEnumerator();
        while (rows.MoveNext())
        {
          int j = sheet.FirstRowNum + 1;
          DataRow dr = dt.NewRow();
          bool hasValue = false;
          foreach (int K in columns)
          {
            dr[K] = GetValueTypeForXLS(sheet.GetRow(K).GetCell(K) as HSSFCell);
            if (dr[K] != null && dr[K].ToString() != string.Empty)
            {
              hasValue = true;
            }
          }
          if (hasValue)
          {
            dt.Rows.Add(dr);
          }
          j++;
        }
        ds.Tables.Add(dt);
      }

      return ds;
    }

    /// <summary>
    /// 根据DataTable导出Excel
    /// </summary>
    /// <param name="dt">DataTable</param>
    /// <param name="file">保存地址</param>
    public static void GetExcelByDataTable(DataTable dt, string file)
    {
      DataSet ds = new DataSet();
      ds.Tables.Add(dt);
      GetExcelByDataSet(ds, file);
    }

    /// <summary>
    /// 根据DataSet导出Excel
    /// </summary>
    /// <param name="ds">DataSet</param>
    /// <param name="file">保存地址</param>
    public static void GetExcelByDataSet(DataSet ds, string file)
    {
      IWorkbook fileWorkbook = new HSSFWorkbook();
      int index = 0;
      foreach (DataTable dt in ds.Tables)
      {
        index++;
        ISheet sheet = fileWorkbook.CreateSheet("Sheet" + index);

        //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);
        }

        //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
      MemoryStream stream = new MemoryStream();
      fileWorkbook.Write(stream);
      var buf = stream.ToArray();

      //保存为Excel文件
      using (FileStream fs = new FileStream(file, FileMode.Create, FileAccess.Write))
      {
        fs.Write(buf, 0, buf.Length);
        fs.Flush();
      }
    }

    /// <summary>
    /// 根据单元格将内容返回为对应类型的数据
    /// </summary>
    /// <param name="cell">单元格</param>
    /// <returns>数据</returns>
    private static object GetValueTypeForXLS(HSSFCell 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;
      }
    }
  }