NPOI 库 C# List<T> 操作类

编写背景：
网上有返回DataTable和DataTable导入Excel的操作，目前系统是以List泛型，所以改成List泛型版的。写的不好请多指教！

public class operateExcel<T>
{
    public operateExcel()
    { 
    }
    /// <summary>
    /// 导出Excel
    /// </summary>
    /// <param name="lists"></param>
    /// <param name="head">中文列名对照</param>
    /// <param name="workbookFile">保存路径</param>
    public void getExcel(List<T> lists,Hashtable head, string workbookFile)
    { 
        try
        {
            HSSFWorkbook workbook = new HSSFWorkbook();
            MemoryStream ms = new MemoryStream();
            HSSFSheet sheet = workbook.CreateSheet() as HSSFSheet;
            HSSFRow headerRow = sheet.CreateRow(0) as HSSFRow;
            bool h = false;
            int j = 1;
            Type type = typeof(T);
            PropertyInfo[] properties = type.GetProperties();

            foreach (T item in lists)
            {
                HSSFRow dataRow = sheet.CreateRow(j) as HSSFRow;
                int i = 0;
                foreach (PropertyInfo column in properties)
                {
                    if (!h)
                    {
                        headerRow.CreateCell(i).SetCellValue(head[column.Name] == null ? column.Name : head[column.Name].ToString());
                        dataRow.CreateCell(i).SetCellValue(column.GetValue(item, null) == null ? "" : column.GetValue(item, null).ToString());
                    }
                    else
                    {
                        dataRow.CreateCell(i).SetCellValue(column.GetValue(item, null) == null ? "" : column.GetValue(item, null).ToString());
                    }

                    i++;
                }
                h = true;
                j++;
            }
            workbook.Write(ms);
            ms.Flush();
            ms.Position = 0;
            sheet = null;
            headerRow = null;
            workbook = null;
            FileStream fs = new FileStream(workbookFile, FileMode.Create, FileAccess.Write);
            byte[] data = ms.ToArray();
            fs.Write(data, 0, data.Length);
            fs.Flush();
            fs.Close();
            data = null;
            ms = null;
            fs = null;
        }
        catch (Exception ee)
        {
            string see = ee.Message;
        }
    }
    /// <summary>
    /// 导入Excel
    /// </summary>
    /// <param name="lists"></param>
    /// <param name="head">中文列名对照</param>
    /// <param name="workbookFile">Excel所在路径</param>
    /// <returns></returns>
    public List<T> fromExcel(Hashtable head, string workbookFile)
    {
        try
        {
            HSSFWorkbook hssfworkbook;
            List<T> lists = new List<T>();
            using (FileStream file = new FileStream(workbookFile, FileMode.Open, FileAccess.Read))
            {
                hssfworkbook = new HSSFWorkbook(file);
            }
            HSSFSheet sheet = hssfworkbook.GetSheetAt(0) as HSSFSheet;
            IEnumerator rows = sheet.GetRowEnumerator();
            HSSFRow headerRow = sheet.GetRow(0) as HSSFRow;
            int cellCount = headerRow.LastCellNum;
            //Type type = typeof(T);
            PropertyInfo[] properties ;
            T t = default(T);
            for (int i = sheet.FirstRowNum + 1; i <= sheet.LastRowNum; i++)
            {
                HSSFRow row = sheet.GetRow(i) as HSSFRow;
                t = Activator.CreateInstance <T>();  
                properties = t.GetType().GetProperties();
                foreach (PropertyInfo column in properties)
                {
                    int j = headerRow.Cells.FindIndex(delegate(Cell c)
                            {
                                return c.StringCellValue==(head[column.Name] == null ? column.Name : head[column.Name].ToString());
                            });
                    if (j>=0&&row.GetCell(j) != null)
                    {
                        object value =valueType(column.PropertyType, row.GetCell(j).ToString());  
                        column.SetValue(t, value, null);
                    }
                }
                lists.Add(t);
            }
            return lists;
        }
        catch (Exception ee)
        {
            string see = ee.Message;
            return null;
        }
    }
    object valueType(Type t, string value)
    {
        object o=null;
        string strt = "String";
        if (t.Name == "Nullable`1")
        {
           strt= t.GetGenericArguments()[0].Name;
        }
        switch (strt)
        {
            case "Decimal":
                o=decimal.Parse(value);
                break;
            case "Int":
                o = int.Parse(value);
                break;
            case "Float":
                o = float.Parse(value);
                break;
            case "DateTime":
                o = DateTime.Parse(value);
                break;
            default:
                o = value;
                break;
        }
        return o;
    }
}