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>