%@ Page Language="C#" AutoEventWireup="true" CodeFile="upload.aspx.cs" Inherits="upload" %>

 !DOCTYPE html>

 html xmlns="http://www.w3.org/1999/xhtml">
 head runat="server">
     meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
     title>/title>
     style type="text/css">
         li
         {
             list-style: none;
             padding-top: 10px;
         }
     /style>
     script type="text/javascript" src="js/jquery-1.6.2.min.js">/script>
     script type="text/javascript">
         function ValidImage(id, msg) {
             $(id).parent().append("span>" + msg + "/span>");
             return false;
         }
     /script>
 /head>
 body>
     form id="form1" runat="server" enctype="multipart/form-data" method="post">
         div>
                       ul>
                 li>
                     input type="file" id="upload1" name="upload" />
                 /li>
                 li>
                     input type="file" id="upload2" name="upload" />
                 /li>
                 li>
                     input type="file" id="upload3" name="upload" />
                 /li>
                 li>
                     input type="file" id="upload4" name="upload" />/li>
                 li>
                     input type="file" id="upload5" name="upload" />

                 /li>
                 li>
                     input type="submit" id="btnPostFile" runat="server" onserverclick="btnPostFile_ServerClick" value="开始上传" />
                 /li>
             /ul>
         /div>
     /form>
 /body>
 /html>

  protected void btnPostFile_ServerClick(object sender, EventArgs e)
     {
         string filePath = Server.MapPath("/uploadImg");
         const int size = 5242880;
         if (!Directory.Exists(filePath))
         {
             Directory.CreateDirectory(filePath);
         }
         if (Request.Files.Count > 0)
         {
             for (int i = 0; i Request.Files.Count; i++)
             {
                 HttpPostedFile postFile = Request.Files[i];
                 string uploadFileID = string.Format("#upload{0}", i + 1);  //当前的上传控件ID,因为jquery要调用就加了#
                 string msg = null;                 //提示信息
                 if (postFile.FileName.Trim().Length = 0)
                 {
                     continue;
                 }
                 if (postFile.ContentLength > size)
                 {
                     msg = "文件太大";
                     Page.ClientScript.RegisterStartupScript(GetType(), "", "ValidImage(" + uploadFileID + "," + msg + ")", true);//将提示信息发送到客户端
                     continue;
                 }
                 string savePath = Path.Combine(filePath, postFile.FileName);        //图片的保存地址
                 if (!File.Exists(savePath))
                 {
                     postFile.SaveAs(Path.Combine(filePath, postFile.FileName));     //如果文件不存在就保存
                 }
                 else
                 {
                     msg = "文件" + postFile.FileName + "已经存在";
                     Page.ClientScript.RegisterStartupScript(GetType(), "", "ValidImage(" + uploadFileID + "," + msg + ")", true);//将提示信息发送到客户端
                     continue;
                 }
                 if (IsImg(savePath))            //通过IsImg方法验证文件是否是图片，或者格式是否正确
                 {
                     SmallImg(postFile.InputStream, postFile.FileName);
                 }
                 else
                 {
                     msg = "只能上传JGP、PNG类型的图片，请检查文件格式是否正确";
                     Page.ClientScript.RegisterStartupScript(GetType(), "", "ValidImage(" + uploadFileID + "," + msg + ")", true);//将提示信息发送到客户端
                     File.Delete(savePath);  //如果不是图片就删除
                 }
             }
         }
     }

  #region 验证上传文件的格式
     /// summary>
     /// 验证上传文件是否是图片
     /// /summary>
     /// param name="FilePath">文件的保存路径/param>
     /// returns>/returns>
     private bool IsImg(string FilePath)
     {
         using (FileStream fs = new FileStream(FilePath, FileMode.Open, FileAccess.Read))
         {
             bool result = false;
             BinaryReader br = new BinaryReader(fs, System.Text.Encoding.UTF8);
             string strImg = "";
             byte buffer;
             try
             {
                 buffer = br.ReadByte();
                 strImg = buffer.ToString();
                 buffer = br.ReadByte();
                 strImg += buffer.ToString();
             }
             catch
             {
                 fs.Close();
                 br.Close();

             }
             if (strImg == "255216" || strImg == "13780")//说明255216是jpg;7173是gif;6677是BMP,13780是PNG;7790是exe,8297是rar
             {
                 result = true;
             }
             return result;
         }
     }
     #endregion

   #region 将图片生成缩略图
     /// summary>
     /// 生成缩略图
     /// /summary>
     private void SmallImg(Stream oStream, string FileName)
     {
         using (System.Drawing.Image img = System.Drawing.Image.FromStream(oStream))
         {
             int newWidth = 100;
             int newHeight = 80;
             int oldWidth = img.Width;
             int oldHeight = img.Height;
             if (oldWidth > oldHeight)
             {
                 newHeight = (int)Math.Floor((double)oldHeight * (double)newWidth / (double)oldWidth);
             }
             else
             {
                 newWidth = (int)Math.Floor((double)oldWidth * (double)newHeight / (double)oldHeight);
             }
             using (Bitmap bmp = new Bitmap(newWidth, newHeight))
             {
                 using (Graphics g = Graphics.FromImage(bmp))
                 {
                     g.Clear(Color.Transparent);
                     g.InterpolationMode = InterpolationMode.High;
                     g.CompositingQuality = CompositingQuality.HighQuality;
                     g.SmoothingMode = SmoothingMode.HighQuality;
                     g.DrawImage(img, new Rectangle(0, 0, newWidth, newHeight), new Rectangle(0, 0, oldWidth, oldHeight), GraphicsUnit.Pixel);
                     string newFileName = Path.GetFileNameWithoutExtension(FileName) + "_small" + Path.GetExtension(FileName);   //缩略图名称
                     string filePath = Server.MapPath("/uploadImg/") + newFileName;
                     bmp.Save(filePath);
                 }
             }

         }
     }
     #endregion