excel帮助类（泛型和datatable）

在做项目的过程中经常会遇到关于excel的导入和导出操作，所以就封装了一个excel帮助类来提升开发的速度。。。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using NPOI.HSSF.UserModel;
using NPOI.HSSF.Util;
using NPOI.XSSF.Util;
using NPOI.XSSF.UserModel;
using NPOI.SS.UserModel;
using log4net;
using System.IO;
using System.Reflection;
using System.Data;

namespace Tools
{
    public class ExcelHelper
    {
        internal static readonly log4net.ILog log = LogManager.GetLogger("log4netlogger");

        #region 导入数据
        /// 从Excel中加载数据（泛型）-  npoi   缺点：不能有datetime？类型
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="fileName">文件名称（用于判断后缀）</param>
        /// <param name="importType">importType 1物理路径上传 2文件流上传 </param>
        /// <param name="filePath">excel文件路径</param>
        /// <param name="stream">文件流</param>
        /// <param name="beginRowIndex">起始行(从0开始)，例如第一行为列头，从第二行开始为数据，则 beginRowIndex = 1</param>
        /// <param name="IsReadComments">是否读取批注 默认为false ;true 读取表头批注 false 读取表头</param>
        /// <returns>泛型列表</returns>
        public static IEnumerable<T> ImportExcel<T>(string fileName, int importType = 1, string filePath = "", Stream stream = null, int beginRowIndex = 1,bool IsReadComments=false) where T : new()
        {
            List<T> resultList = new List<T>();
            List<string> colName = new List<string>();
            Dictionary<int, string> dicColName = new Dictionary<int, string>();
            try
            {
                var fileExt = Path.GetExtension(fileName).ToLower();//获取文件后缀
                IWorkbook workbook;
                if (importType == 1)
                {
                    stream = new FileStream(filePath, FileMode.Open);
                }

                if (fileExt == ".xls")
                    workbook = new HSSFWorkbook(stream);
                else if (fileExt == ".xlsx")
                    workbook = new XSSFWorkbook(stream);
                else
                    return resultList;


                ISheet sheet = workbook.GetSheetAt(0);//获取sheet

                int rowStart = sheet.FirstRowNum;//开始行
                int rowEnd = sheet.LastRowNum;//结束行

                if (rowEnd >= 0)
                {
                    int colStart = sheet.GetRow(rowStart).FirstCellNum;//开始列
                    int colEnd = sheet.GetRow(rowStart).LastCellNum;//结束列

                    var firstRow = sheet.GetRow(rowStart);
        
                    //判断读取批注还是表头
                    if (IsReadComments == true)
                    {    
                        //处理表头 
                        for (int i = colStart; i < colEnd; i++)
                        {
                            var value = firstRow.GetCell(i);
                            dicColName[i] = value == null ? "" : value.CellComment.String.String.ToLower();//获取批注
                        }
                    }
                    else
                    {
                        for (int i = colStart; i < colEnd; i++)
                        {
                            var value = firstRow.GetCell(i);
                            dicColName[i] = value == null ? "" : value.ToString();
                        }
                    }

                    List<PropertyInfo> propertyInfoList = new List<PropertyInfo>(typeof(T).GetProperties());
                    propertyInfoList = propertyInfoList.Where(p => dicColName.Values.Contains(p.Name)).ToList();

                    for (int i = rowStart + beginRowIndex; i <= rowEnd; i++)
                    {
                        var row = sheet.GetRow(i);//获取行
                        if (row == null)