npoi导出excel 导出List<T>

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

namespace CommonHelper
{
   public class ExcelHelper 
    {

       public ExcelHelper() { }

       /// <summary>
       /// 文件流初始化对象
       /// </summary>
       /// <param name="stream"></param>
       public ExcelHelper(Stream stream) 
       {
           _IWorkbook = CreateWorkbook(stream);
       }

       /// <summary>
       /// 传入文件名
       /// </summary>
       /// <param name="fileName"></param>
       public ExcelHelper(string fileName) 
       {
           using (FileStream fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read))
           {
               _IWorkbook = CreateWorkbook(fileStream);
           }
       }

       /// <summary>
       /// 工作薄
       /// </summary>
       private IWorkbook _IWorkbook;

       /// <summary>
       /// 创建工作簿对象
       /// </summary>
       /// <param name="stream"></param>
       /// <returns></returns>
       private IWorkbook CreateWorkbook(Stream stream) 
       {
           try 
           {
              return new XSSFWorkbook(stream); //07
           }
           catch
           {
              return new HSSFWorkbook(stream); //03
           }
          
       }

       /// <summary>
       /// 把Sheet中的数据转换为DataTable
       /// </summary>
       /// <param name="sheet"></param>
       /// <returns></returns>
       private DataTable ExportToDataTable(ISheet sheet) 
       {
           DataTable dt = new DataTable();

           //默认，第一行是字段
           IRow headRow = sheet.GetRow(0);

           //设置datatable字段
           for (int i = headRow.FirstCellNum, len = headRow.LastCellNum; i < len; i++)
           {
               dt.Columns.Add(headRow.Cells[i].StringCellValue);
           }
           //遍历数据行
           for (int i = (sheet.FirstRowNum + 1), len = sheet.LastRowNum + 1; i < len; i++)
           {
               IRow tempRow = sheet.GetRow(i);
               DataRow dataRow = dt.NewRow();

               //遍历一行的每一个单元格
               for (int r = 0, j = tempRow.FirstCellNum, len2 = tempRow.LastCellNum; j < len2; j++, r++)
               {

                   ICell cell = tempRow.GetCell(j);

                   if (cell != null)
                   {
                       switch (cell.CellType)
                       {
                           case CellType.STRING:
                               dataRow[r] = cell.StringCellValue;
                               break;
                           case CellType.NUMERIC:
                               dataRow[r] = cell.NumericCellValue;
                               break;
                           case CellType.BOOLEAN:
                               dataRow[r] = cell.BooleanCellValue;
                               break;
                           default: dataRow[r] = "ERROR";
                               break;
                       }
                   }
               }
               dt.Rows.Add(dataRow);
           }
           return dt;
       }

       /// <summary>
       /// Sheet中的数据转换为List集合
       /// </summary>
       /// <param name="sheet"></param>
       /// <param name="fields"></param>
       /// <returns></returns>
       private IList<T> ExportToList<T>(ISheet sheet,string[] fields) where T:class,new()
       {
            IList<T> list = new List<T>();

           //遍历每一行数据
           for (int i = sheet.FirstRowNum + 1, len = sheet.LastRowNum + 1; i < len; i++) 
           {
               T t=new T();
               IRow row = sheet.GetRow(i);

               for (int j = 0, len2 = fields.Length; j < len2; j++)
               {
                   ICell cell=row.GetCell(j);
                   object cellValue= null;

                   switch (cell.CellType) 
                   {
                       case CellType.STRING: //文本
                           cellValue = cell.StringCellValue;
                           break;
                       case CellType.NUMERIC: //数值
                           cellValue =Convert.ToInt32(cell.NumericCellValue);//Double转换为int
                           break;
                       case CellType.BOOLEAN: //bool
                           cellValue = cell.BooleanCellValue;
                           break;
                       case CellType.BLANK: //空白
                           cellValue = "";
                           break;
                       default: cellValue = "ERROR";
                           break;
                   }

                   typeof(T).GetProperty(fields[j]).SetValue(t,cellValue,null);
               }
               list.Add(t);
           }

               return list;
       }

       /// <summary>
       /// 获取第一个Sheet的第X行，第Y列的值。起始点为1
       /// </summary>
       /// <param name="X">行</param>
       /// <param name="Y">列</param>
       /// <returns></returns>
       public string GetCellValue(int X, int Y) 
       {
           ISheet sheet = _IWorkbook.GetSheetAt(0);

           IRow row = sheet.GetRow(X-1);

           return row.GetCell(Y-1).ToString();
       }

       /// <summary>
       /// 获取一行的所有数据
       /// </summary>
       /// <param name="X">第x行</param>
       /// <returns></returns>
       public string[] GetCells(int X) 
       {
           List<string> list = new List<string>();

           ISheet sheet = _IWorkbook.GetSheetAt(0);

           IRow row = sheet.GetRow(X-1);

           for (int i = 0, len = row.LastCellNum; i < len; i++) 
           {
               list.Add(row.GetCell(i).StringCellValue);//这里没有考虑数据格式转换，会出现bug
           }
           return list.ToArray();
       }

       /// <summary>
       /// 第一个Sheet数据，转换为DataTable
       /// </summary>
       /// <returns></returns>
       public DataTable ExportExcelToDataTable() 
       {
           return ExportToDataTable(_IWorkbook.GetSheetAt(0));
       }

       /// <summary>
       /// 第sheetIndex表数据，转换为DataTable
       /// </summary>
       /// <param name="sheetIndex">第几个Sheet，从1开始</param>
       /// <returns></returns>
       public DataTable ExportExcelToDataTable(int sheetIndex) 
       {
           return ExportToDataTable(_IWorkbook.GetSheetAt(sheetIndex-1));
       }


       /// <summary>
       /// Excel中默认第一张Sheet导出到集合
       /// </summary>
       /// <param name="fields">Excel各个列，依次要转换成为的对象字段名称</param>
       /// <returns></returns>
       public IList<T> ExcelToList<T>(string[] fields) where T:class,new ()
       {
           return ExportToList<T>(_IWorkbook.GetSheetAt(0),fields);
       }

       /// <summary>
       /// Excel中指定的Sheet导出到集合
       /// </summary>
       /// <param name="sheetIndex">第几张Sheet,从1开始</param>
       /// <param name="fields">Excel各个列，依次要转换成为的对象字段名称</param>
       /// <returns></returns>
       public IList<T> ExcelToList<T>(int sheetIndex,string[] fields) where T:class,new()
       {
          return ExportToList<T>(_IWorkbook.GetSheetAt(sheetIndex-1), fields);
       }

    }
}