#region 取得文件后缀
        /// <summary> 
        /// 取得文件后缀 
        /// </summary> 
        /// <param name="filename">文件名称</param> 
        /// <returns></returns> 
        public static string GetFileExtends(string filename)
        {
            string ext = null;
            if (filename.IndexOf('.') > 0)
            {
                string[] fs = filename.Split('.');
                ext = fs[fs.Length - 1];
            }
            return ext;
        }
        #endregion

        #region 获取链接字符串
        /// <summary>
        /// 获取链接字符串
        /// </summary>
        /// <param name="filepath">相对路径</param>
        /// <returns>链接字符串</returns>
        private static string getconstring(string filepath)
        {
            string constring;
            if (filepath.EndsWith(".xls"))
            {
                // Excel 97-2003
                constring = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source={0};Extended Properties='Excel 8.0;HDR=YES;IMEX=1'";
            }
            else
            {
                // Excel 2007
                constring = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties='Excel 12.0 Xml;HDR=YES;'";
            }
            return string.Format(constring, System.Web.HttpContext.Current.Server.MapPath(filepath));
        }
        #endregion

        #region 读取excel表格sheet的名称
        /// <summary>
        /// 读取excel表格sheet的名称
        /// </summary>
        /// <param name="filepath">相对路径</param>
        /// <returns>excel表格sheet的名称数组</returns>
        public static string[] getexcelsheetnames(string filepath)
        {
            using (OleDbConnection con = new OleDbConnection(getconstring(filepath)))
            {
                con.Open();
                DataTable dt = con.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, null);
                con.Close();
                if (dt == null)
                {
                    return null;
                }
                string[] excelsheetnames = new string[dt.Rows.Count];
                int i = 0;
                foreach (DataRow dr in dt.Rows)
                {
                    excelsheetnames[i++] = dr["table_name"].ToString();
                }
                return excelsheetnames;
            }
        }
        #endregion

        #region 读取excel文件
        /// <summary>
        /// 读取excel文件
        /// </summary>
        /// <param name="filepath">相对路径</param>
        /// <param name="sheetname">查询Excel表格sheet的名称</param>
        /// <returns>DataTable</returns>
        public static DataTable readexcel(string filepath, string sheetname)
        {
            using (OleDbConnection con = new OleDbConnection(getconstring(filepath)))
            {
                if (string.IsNullOrEmpty(sheetname))
                {
                    sheetname = getexcelsheetnames(filepath)[0];//如果Excel表格sheet的名称为空，给个默认值
                }
                using (OleDbDataAdapter oda = new OleDbDataAdapter(string.Format("select * from [{0}]", sheetname), con))
                {
                    DataTable dt = new DataTable();
                    
                    con.Open();
                    oda.Fill(dt);
                    con.Close();
                    return dt;
                }
            }
        }
        #endregion