文件（图片生产缩略图）的上传与下载

一、文件（图片）保存到数据库
//得到用户要上传的文件名
            string strFilePathName = loFile.PostedFile.FileName;
            string strFileName = Path.GetFileName(strFilePathName);
            int FileLength = loFile.PostedFile.ContentLength;
            if(FileLength<=0)
                return;
            try
            {//上传文件
                Byte[] FileByteArray = new Byte[FileLength]; //图象文件临时储存Byte数组
                Stream StreamObject = loFile.PostedFile.InputStream; //建立数据流对像
                //读取图象文件数据，FileByteArray为数据储存体，0为数据指针位置、FileLnegth为数据长度
                StreamObject.Read(FileByteArray,0,FileLength); 
                //建立SQL Server链接
                string strCon = System.Configuration.ConfigurationSettings.AppSettings["DSN"];
                SqlConnection Con = new SqlConnection(strCon);
                String SqlCmd = "INSERT INTO ImageStore (ImageData, ImageContentType, ImageDescription, ImageSize) VALUES (@Image, @ContentType, @ImageDescription, @ImageSize)";
                SqlCommand CmdObj = new SqlCommand(SqlCmd, Con);
                CmdObj.Parameters.Add("@Image",SqlDbType.Binary, FileLength).Value = FileByteArray;
                CmdObj.Parameters.Add("@ContentType", SqlDbType.VarChar,50).Value = loFile.PostedFile.ContentType; //记录文件类型
                //把其它单表数据记录上传
                CmdObj.Parameters.Add("@ImageDescription", SqlDbType.VarChar,200).Value = tbDescription.Text;
                //记录文件长度，读取时使用
                CmdObj.Parameters.Add("@ImageSize", SqlDbType.BigInt,8).Value = FileLength;
                Con.Open();
                CmdObj.ExecuteNonQuery(); 
                Con.Close();
                //跳转页面
                Response.Redirect("ShowAll.aspx");
            }
            catch
            {
            }

取出来显示：
int ImgID = Convert.ToInt32(Request.QueryString["ID"]); //ID为图片ID 
            //建立数据库链接
            string strCon = System.Configuration.ConfigurationSettings.AppSettings["DSN"];
            SqlConnection Con = new SqlConnection(strCon);
            String SqlCmd = "SELECT * FROM ImageStore WHERE ImageID = @ImageID";
            SqlCommand CmdObj = new SqlCommand(SqlCmd, Con);
            CmdObj.Parameters.Add("@ImageID", SqlDbType.Int).Value = ImgID;
            Con.Open();
            SqlDataReader SqlReader = CmdObj.ExecuteReader();
            SqlReader.Read(); 
            Response.ContentType = (string)SqlReader["ImageContentType"];//设定输出文件类型
            //输出图象文件二进制数制
            Response.OutputStream.Write((byte[])SqlReader["ImageData"], 0, (int)SqlReader["ImageSize"]); 
            Response.End();
            //也可以保存为图像
//            FileStream fs = new FileStream(@"C:\aa.BMP", FileMode.OpenOrCreate, FileAccess.Write);
//            fs.Write((byte[])SqlReader["ImageData"], 0,(int)SqlReader["ImageSize"]);
//            fs.Close();

            Con.Close();

二、文件（图片）保存到硬盘   
方法一  /// <summary>
 2        /// 下载文件
 3        /// </summary>
 4        /// <param name="filename">文件物理地址</param>
 5        protected void DownloadFile(string filename)
 6        {
 7
 8            string saveFileName = "test.xls";
 9            int intStart = filename.LastIndexOf("\\")+1;
10            saveFileName = filename.Substring(intStart,filename.Length-intStart);
11
12            System.IO.FileInfo fi=new System.IO.FileInfo(filename);
13            string fileextname=fi.Extension;
14            string DEFAULT_CONTENT_TYPE = "application/unknown";
15            RegistryKey regkey,fileextkey;
16            string filecontenttype;
17            try 
18            {                
19                regkey=Registry.ClassesRoot;                
20                fileextkey=regkey.OpenSubKey(fileextname);                
21                filecontenttype=fileextkey.GetValue("Content Type",DEFAULT_CONTENT_TYPE).ToString();
22            }
23            catch
24            {
25                filecontenttype=DEFAULT_CONTENT_TYPE;
26            }      
27
28
29            Response.Clear();
30            Response.Charset = "utf-8";
31            Response.Buffer= true;
32            this.EnableViewState = false;
33            Response.ContentEncoding = System.Text.Encoding.UTF8;
34
35            Response.AppendHeader("Content-Disposition","attachment;filename=" + saveFileName); 
36            Response.ContentType=filecontenttype;
37
38            Response.WriteFile(filename); 
39            Response.Flush();
40            Response.Close();
41
42            Response.End();
43        }
44    
方法二
  /// <summary>
 2        /// 下载文件
 3        /// </summary>
 4        /// <param name="filename">文件物理地址</param>
 5        protected void DownloadFile(string filename)
 6        {
 7            string saveFileName = "test.xls";
 8            int intStart = filename.LastIndexOf("\\")+1;
 9            saveFileName = filename.Substring(intStart,filename.Length-intStart);
10
11            Response.Clear();
12            Response.Charset = "utf-8";
13            Response.Buffer= true;
14            this.EnableViewState = false;
15            Response.ContentEncoding = System.Text.Encoding.UTF8;
16
17            Response.AppendHeader("Content-Disposition","attachment;filename=" + saveFileName); 
18            Response.WriteFile(filename); 
19            Response.Flush();
20            Response.Close();
21
22            Response.End();
23        }文件的ContentType类型 小全
出现提示框

string strFile="F:\\a.doc";//路径根据实际情况而定
if(!System.IO.File.Exists(strFile))
   {
    Response.Write("<script language='javascript'>alert('对不起，文件不存在！');</script>");
    return;
   }
   Response.Clear();
   Response.ClearHeaders();
   Response.Charset = "GB2312";
   Response.ContentEncoding =System.Text.Encoding.UTF8;
   Response.ContentType = "application/octet-stream"; 
   FileInfo fi=new FileInfo(strFile);
   Response.AddHeader("Content-Disposition","attachment;  filename="  +  HttpUtility.UrlEncode(fi.Name)) ;
   Response.AddHeader("Content-Length",fi.Length.ToString());
   byte[] tmpbyte=new byte[1024*8];
   FileStream fs=fi.OpenRead();
   int count;
   while((count=fs.Read(tmpbyte,0,tmpbyte.Length))>0)
   {
    Response.BinaryWrite(tmpbyte);
    Response.Flush();
   }
   fs.Close();   
   Response.End();

直接在浏览器中打开
   string strFile="F:\\a.doc";//路径根据实际情况而定
   Response.Clear();
   Response.ClearHeaders();
   Response.Charset = "GB2312";
   Response.ContentEncoding =System.Text.Encoding.UTF8;
   Response.ContentType = "application/msword"; 
   Response.WriteFile(strFile);

/// <summary>
 2        /// 上传图片
 3        /// </summary>
 4        /// <param name="sender"></param>  
 5        /// <param name="e"></param>
 6        /// <returns>操作结果</returns>
 7        private bool ImageUpload(int nWidth,int nHeight)
 8        {
 9            System.Web.HttpFileCollection files = Request.Files;
10            System.Web.HttpPostedFile pf = files[0];
11            string sOldPath = pf.FileName.ToString();
12            int i = sOldPath.LastIndexOf("\\");
13            string sOldName = sOldPath.Substring(i+1,sOldPath.Length-i-1);
14            //"L"代表大图 && "S"代表缩略图
15            string sTimeNo = System.DateTime.Now.ToString("yyMMddHHmmss");
16            string sNewNameL = "L"+sTimeNo+"_"+sOldName;
17            string sNewNameS = sNewNameL.Replace("L"+sTimeNo,"S"+sTimeNo);
18            string sNewPathL = Server.MapPath("../images/uploadfiles/")+sNewNameL;
19            string sNewPathS = Server.MapPath("../images/uploadfiles/")+sNewNameS;
20            if(System.IO.File.Exists(sNewPathL)||System.IO.File.Exists(sNewPathS))
21            {
22                Page.RegisterStartupScript("FailToUpload","<script>alert('文件名已存在！');</script>");
23                return false;
24            }
25            else
26            {
27                pf.SaveAs(sNewPathL);//保存原图
28                string strContentType = pf.ContentType.ToString();
29                if(strContentType.IndexOf("image/")<0)
30                {
31                    Page.RegisterStartupScript("KeyEro","<script>alert('无效的图片格式！');</script>");
32                    return false;
33                }
34                else
35                {
36                    this.GetThumbNail(sOldPath,strContentType,sNewPathS,nWidth, nHeight);
37                    this.Image1.ImageUrl = sNewPathS;
38                    return true;
39                }
40            }
41        }
42        /// <summary>
43        /// 生成缩略图
44        /// </summary>
45        /// <param name="FileName">待上传文件的完全限定名</param>
46        /// <param name="strContentType">待上传文件的内容类型</param>
47        /// <param name="path">路径</param>
48        /// <param name="nWidth">宽</param>
49        /// <param name="nHeight">高</param>
50        private void GetThumbNail(string FileName,string strContentType,string path,int nWidth,int nHeight)
51        {
52            System.Drawing.Image oImage;
53            oImage = System.Drawing.Image.FromFile(FileName);
54            oImage = oImage.GetThumbnailImage(nWidth,nHeight,null,IntPtr.Zero);
55            //            MemoryStream ms = new MemoryStream();
56            //            Response.ContentType = strContentType;
57            //            oImage.Save(ms,strContentType);
58            oImage.Save(path,this.GetContenType(strContentType));
59            //            ms.WriteTo(Response.OutputStream);
60        }
61        /// <summary>
62        /// 获取保存文件的格式
63        /// </summary>
64        /// <param name="strContentType">待上传文件的内容类型</param>
65        /// <returns>文件格式</returns>
66        private System.Drawing.Imaging.ImageFormat GetContenType(string strContentType)
67        {
68            //只写少数几种格式
69            if(strContentType.ToString().ToLower()== "image/bmp")
70                return System.Drawing.Imaging.ImageFormat.Bmp;
71            else if(strContentType.ToString().ToLower()== "image/gif")
72                return System.Drawing.Imaging.ImageFormat.Gif;
73            else
74            return System.Drawing.Imaging.ImageFormat.Jpeg;
75        }
For example:

Response.ContentType = "image/jpeg";Response.AppendHeader("Content-Disposition","attachment; filename=SailBig.jpg");Response.TransmitFile( Server.MapPath("~/images/sailbig.jpg") );Response.End();
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原文地址：https://www.cnblogs.com/ghd258/p/256596.html