过滤上传文件的扩展名

/**//// <summary>
        /// 取文件的扩展名：例如：aspx ,asp  ,asa  .......
        /// </summary>
        /// <param name="strOriginal"></param>
        /// <param name="strSymbol"></param>
        /// <returns></returns>
        public string GetLastStr(string strOriginal,string strSymbol)
        ...{
            int strPlace=strOriginal.LastIndexOf(strSymbol)+strSymbol.Length;
            strOriginal=strOriginal.Substring(strPlace);
            return strOriginal;
        }

        /**//// <summary>
        /// 事件
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Button1_Click(object sender, System.EventArgs e)
        ...{
            try
            ...{
                string noFile = "aspx|asp|asa|exe|dll|js|vbs|bat|htm|html|shtml|xhtml";  
                string strname = GetLastStr(File1.PostedFile.FileName,".");
                int n =noFile.IndexOf(strname.ToLower());
                if(noFile.IndexOf(strname.ToLower()) >= 0)
                ...{
                    Response.Write("<script>alert(' 请不要上传非法文件....')</script>");
                }
            }
            catch(System.Exception er)
            ...{
                Response.Write("<font color=red>"+er.Message+"</font>");
            }
        }