需求说明：

      实际项目中，有必要上传附件（包括图片、文档、解压文件等）对数据库数据完善，这里实现的功能就是，上传附件到数据库，然后从数据读出来之后，可以“点击下载”之前上传的附件内容。

asp.net代码如下：

//用FileUpload控件，上传附件之后，导入数据库操作
        protected void btnUp_Click(object sender, EventArgs e)
        {
            DbSql db = new DbSql();  //数据操作类
            string fileName = "";
            string fielurl = "";
            if (filePhoto.HasFile)
            {
                fileName = filePhoto.FileName;

                if (!ValidateFileType(fileName))  //上传文件类型判断
                {
                    Response.Write("<script>alert('不支持文件！')</script>");
                    return;
                }

                fileName = fileName.Replace(":", "_").Replace(" ", "_").Replace("\\", "_").Replace("/", "_");
                fileName = DateTime.Now.Ticks.ToString() + "_" + fileName;

                filePhoto.SaveAs(Server.MapPath("~/upload/" + fileName));



                string strr = "~/upload/" + fileName + "";
                fielurl = "<a href=http://www.mamicode.com/MidDownFile.aspx?fileUrl=" + Server.UrlEncode(strr) + ">点击下载";//用MidDownFile页面，处理对上传文件的下载>下面是判断上传文件类型的一个使用方法
#region 上传文件类型判断
        protected readonly static List<string> VALID_FILE_TYPES = new List<string> { "jpg", "bmp", "gif", "jpeg", "png", "rar", "txt", "doc", "docx" };

        protected static bool ValidateFileType(string fileName)
        {
            string fileType = String.Empty;
            int lastDotIndex = fileName.LastIndexOf(".");
            if (lastDotIndex >= 0)
            {
                fileType = fileName.Substring(lastDotIndex + 1).ToLower();
            }

            if (VALID_FILE_TYPES.Contains(fileType))
            {
                return true;
            }
            else
            {
                return false;
            }
        }
        #endregion
接下来是MidDownFile.aspx页面处理对上传文件的下载
 protected void Page_Load(object sender, EventArgs e)
        {
            string fileName = Server.UrlDecode(Request.QueryString["fileUrl"]);
            WriteF(fileName);
        }
        public void WriteF(string fileName)
        {
            if (System.IO.File.Exists(Server.MapPath(fileName)))
            {
                Response.ContentType = "application/x-zip-compressed";
                Response.AddHeader("Content-Disposition", "attachment;filename=" + System.IO.Path.GetFileName(fileName) + "");
                string filename = Server.MapPath(fileName);
                Response.TransmitFile(filename);
            }
            else
            {
                Response.Write("文件不存在！");
            }
        }