upload上传单张图片

protected void btnpic_upload_Click(object sender, EventArgs e)
  { 
   #region 上传文件
   Boolean fileOk = false;
   if (pic_upload.HasFile)//验证是否包含文件
   {
    //取得文件的扩展名,并转换成小写
    string fileExtension = Path.GetExtension(pic_upload.FileName).ToLower();
    //验证上传文件是否图片格式
    fileOk = IsImage(fileExtension);

    if (fileOk)
    {
     //对上传文件的大小进行检测，限定文件最大不超过8M
     if (pic_upload.PostedFile.ContentLength < 8192000)
     {

      string filepath = "~/Admin/I_Institution/Images/";
      if (Directory.Exists(Server.MapPath(filepath)) == false)//如果不存在就创建file文件夹
      {
       Directory.CreateDirectory(Server.MapPath(filepath));
      }
      string virpath = filepath + CreatePasswordHash(pic_upload.FileName, 4) + fileExtension;//这是存到服务器上的虚拟路径
      string mappath = Server.MapPath(virpath);//转换成服务器上的物理路径
      pic.Visible = true;

      pic_upload.PostedFile.SaveAs(mappath);//保存图片
      //显示图片
      pic.ImageUrl = virpath;
      lbl_pic.Visible = true;
      //清空提示
      lbl_pic.Text = "上传成功";
     }
     else
     {
      pic.Visible = false;
      lbl_pic.Visible = true;
      pic.ImageUrl = "";
      lbl_pic.Text = "文件大小超出8M！请重新选择！";
     }
    }
    else
    {
     lbl_pic.Visible = false;
     pic.ImageUrl = "";
     lbl_pic.Text = "要上传的文件类型不对！请重新选择！";
    }
   }
   else
   {
    lbl_pic.Visible = false;
    pic.ImageUrl = "";
    lbl_pic.Text = "请选择要上传的图片！";
   }
   #endregion
  }

  /// <summary>
  /// 验证是否指定的图片格式
  /// </summary>
  /// <param name="str"></param>
  /// <returns></returns>
  public bool IsImage(string str)
  {
   bool isimage = false;
   string thestr = str.ToLower();
   //限定只能上传jpg和gif图片
   string[] allowExtension = { ".jpg", ".gif", ".bmp", ".png" };
   //对上传的文件的类型进行一个个匹对
   for (int i = 0; i < allowExtension.Length; i++)
   {
    if (thestr == allowExtension[i])
    {
     isimage = true;
     break;
    }
   }
   return isimage;
  }

  /// <summary>
  /// 创建一个指定长度的随机salt值
  /// </summary>
  public string CreateSalt(int saltLenght)
  {
   //生成一个加密的随机数
   RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
   byte[] buff = new byte[saltLenght];
   rng.GetBytes(buff);
   //返回一个Base64随机数的字符串
   return Convert.ToBase64String(buff);
  }

  /// <summary>
  /// 返回加密后的字符串
  /// </summary>
  public string CreatePasswordHash(string pwd, int saltLenght)
  {
   string strSalt = CreateSalt(saltLenght);
   //把密码和Salt连起来
   string saltAndPwd = String.Concat(pwd, strSalt);
   //对密码进行哈希
   string hashenPwd = FormsAuthentication.HashPasswordForStoringInConfigFile(saltAndPwd, "sha1");
   //转为小写字符并截取前16个字符串
   hashenPwd = hashenPwd.ToLower().Substring(0, 16);
   //返回哈希后的值
   return hashenPwd;
  }

tr>
      <td height="25" width="30%" align="right">
       机构图标路径 
      </td>
      <td height="25" width="" align="left">
       <asp:Image ID="pic" runat="server" Width="200px" Visible="False" /><br />
       <asp:FileUpload ID="pic_upload" runat="server" />
       <asp:Button ID="btnpic_upload" runat="server" Text="图片开始上传" OnClick="btnpic_upload_Click" /><br />
       <asp:Label ID="lbl_pic" runat="server" Text="" Visible="False"></asp:Label>
      </td>
     </tr>