??????????????????????????????????ж?

    try
                {
                    //?ж????????????
                    if (FileUpload1.HasFile)
                    {
                        if (IsAllowedExtension(FileUpload1))
                        {
                            string path = Server.MapPath("~/images/");
                            FileUpload1.PostedFile.SaveAs(path + FileUpload1.FileName);
                            Response.Write("<script>alert('??????');</script>");
                        }
                        else
                        {
                            Response.Write("<script>alert('????????jpg????gif??');</script>");
                        }
     
                    }
                    else
                    {
                        Response.Write("<script>alert('???????????');</script>");
                    }
                }
                catch (Exception error)
                {
                    Response.Write(error.ToString());
                }
                #endregion
            }
    //?????ж???????????????
            public static bool IsAllowedExtension(FileUpload hifile)
            {
                System.IO.FileStream fs = new System.IO.FileStream(hifile.PostedFile.FileName?? System.IO.FileMode.Open?? System.IO.FileAccess.Read);
                System.IO.BinaryReader r = new System.IO.BinaryReader(fs);
                string fileclass = "";
                //?????λ????????ж?.
                byte buffer;
                try
                {
                    buffer = r.ReadByte();
                    fileclass = buffer.ToString();
                    buffer = r.ReadByte();
                    fileclass += buffer.ToString();
     
                }
                catch
                {
     
                }
                r.Close();
                fs.Close();
                if (fileclass == "255216" || fileclass == "7173")//???255216??jpg;7173??gif;6677??BMP??13780??PNG;7790??exe??8297??rar
                {
                    return true;
                }
                else
                {
                    return false;
                }
     
            }