????????????????????????1.txt???1.jpg?????????????????????????????????????????????????????????????

    Boolean fileOk = false;
              string path = Server.MapPath("~/images/");
              //?ж????????????
              if (FileUpload1.HasFile)
              {
                  //??????????????????????Сд
                  string fileExtension = System.IO.Path.GetExtension(FileUpload1.FileName).ToLower();
                  //?????????jpg??gif??
                  string[] allowExtension = { ".jpg"?? ".gif" };
                  //???????????????????????????
                  int j = 0;
                  for (int i = 0; i < allowExtension.Length; i++)
                  {
                      if (fileExtension == allowExtension[i])
                      {
                          fileOk = true;
                          return;
                      }
                      else
                      {
                          j++;
                      }
                  }
                  if (j > 0)
                  {
                      Response.Write("<script>alert('???????????');</script>");
                      return;
                  }
              }
              else
              {
                  Response.Write("<script>alert('???????????');</script>");
                  return;
              }
              //???????????????????????
              if (fileOk)
              {
                  FileUpload1.PostedFile.SaveAs(path + FileUpload1.FileName);
                  Response.Write("<script>alert('??????');</script>");
              }

????????????????????????????MIME?????????

    Boolean fileOk = false;
               string path = Server.MapPath("~/images/");
               //?ж????????????
               if (FileUpload1.HasFile)
               {
                   //??????MIME????????
                   string type = this.FileUpload1.PostedFile.ContentType.ToLower();
                   if (type.Contains("image"))    //????MIME?????"image/xxx"????????ж????????
                   {
                       fileOk = true;
     
                   }
                   else
                   {
                       Response.Write("<script>alert('????????')</script>");
                   }
               }
               else
               {
                   Response.Write("<script>alert('???????????');</script>");
               }
               //???????????????????????
               if (fileOk)
               {
                   FileUpload1.PostedFile.SaveAs(path + FileUpload1.FileName);
                   Response.Write("<script>alert('??????');</script>");
               }