html5 新特性 

 <input id="imgsf" type="file" name="imgsf" multiple  />

input  file 中增加 multiple   属性可以选择多文件。IE9以下版本不兼容

    <form id="form1" method="post" action="upload_json.ashx" enctype="multipart/form-data">

    <div>

     <input id="imgsf" type="file" name="imgsf" multiple  />

        <input type="text" name="ceshi" value="panlitao" >

        <input type="submit" value="提交" />

    </div>

    </form>

//预览js

  <div id="imgrq">

    </div>

     <script type="text/javascript">

         $("#imgsf").change(function () {

             var filedx = 0;

             for (var i = 0, j = this.files.length; i < j; i++) {

                 $("#imgrq").append("<img  src=\"" + window.URL.createObjectURL(this.files[i]) + "\" width=\"100\" height=\"100\" />");

             }

         });

    </script>

C# 代码

 public class upload_json : IHttpHandler

    {

       // private HttpContext context;

        public void ProcessRequest(HttpContext context)

        {

            String aspxUrl = context.Request.Path.Substring(0, context.Request.Path.LastIndexOf("/") + 1);

            //文件保存目录路径

            String savePath = "attached/";

            //文件保存目录URL

            String saveUrl = aspxUrl + "attached/";

            //定义允许上传的文件扩展名

            Hashtable extTable = new Hashtable();

            extTable.Add("image", "gif,jpg,jpeg,png,bmp");

            //extTable.Add("flash", "swf,flv");

            //extTable.Add("media", "swf,flv,mp3,wav,wma,wmv,mid,avi,mpg,asf,rm,rmvb");

            //extTable.Add("file", "doc,docx,xls,xlsx,ppt,htm,html,txt,zip,rar,gz,bz2");

            //最大文件大小

            int maxSize = 1000000;

          //  this.context = context;

            String newFileName = "";

            for (int i = 0; i < context.Request.Files.Count;i++ )

            {

                HttpPostedFile imgFile = context.Request.Files[i];

                if (imgFile == null)

                {

                    showError("请选择文件。");

                }

                String dirPath = context.Server.MapPath(savePath);

                if (!Directory.Exists(dirPath))

                {

                    showError("上传目录不存在。");

                }

                String dirName = context.Request.QueryString["dir"];

                if (String.IsNullOrEmpty(dirName))

                {

                    dirName = "image";

                }

                if (!extTable.ContainsKey(dirName))

                {

                    showError("目录名不正确。");

                }

                String fileName = imgFile.FileName;

                String fileExt = Path.GetExtension(fileName).ToLower();

                if (imgFile.InputStream == null || imgFile.InputStream.Length > maxSize)

                {

                    showError("上传文件大小超过限制。");

                }

                //修改为文件流去判断文件格式

                // string exPath = mall_bll.Common.isfilltype(stream: imgFile.InputStream).ToLower();

                //  if (exPath != "jpg" && exPath != "gif" && exPath != "bmp" && exPath != "png")

                //   { showError("上传文件扩展名是不允许的扩展名。\n只允许" + ((String)extTable[dirName]) + "格式。"); }

                //if (String.IsNullOrEmpty(fileExt) || Array.IndexOf(((String)extTable[dirName]).Split(','), fileExt.Substring(1).ToLower()) == -1)

                //{

                //    showError("上传文件扩展名是不允许的扩展名。\n只允许" + ((String)extTable[dirName]) + "格式。");

                //}

                //创建文件夹

                dirPath += dirName + "/";

                saveUrl += dirName + "/";

                if (!Directory.Exists(dirPath))

                {

                    Directory.CreateDirectory(dirPath);

                }

                String ymd = DateTime.Now.ToString("yyyyMMdd", DateTimeFormatInfo.InvariantInfo);

                dirPath += ymd + "/";

                saveUrl += ymd + "/";

                if (!Directory.Exists(dirPath))

                {

                    Directory.CreateDirectory(dirPath);

                }

                 newFileName = DateTime.Now.ToString("yyyyMMddHHmmss_ffff", DateTimeFormatInfo.InvariantInfo) + fileExt;

                String filePath = dirPath + newFileName;

                imgFile.SaveAs(filePath);

            }

            String fileUrl = saveUrl + newFileName;

            Hashtable hash = new Hashtable();

            hash["error"] = 0;

            hash["url"] = fileUrl;

            context.Response.AddHeader("Content-Type", "text/html; charset=UTF-8");

         //   context.Response.Write(JsonMapper.ToJson(hash));

            context.Response.End();

        }

        private void showError(string message)

        {

            Hashtable hash = new Hashtable();

            hash["error"] = 1;

            hash["message"] = message;

         //   context.Response.AddHeader("Content-Type", "text/html; charset=UTF-8");

         //   context.Response.Write(JsonMapper.ToJson(hash));

       //     context.Response.End();

        }

        public bool IsReusable

        {

            get

            {

                return true;

            }

        }

    }