public class UploadController : Controller

    {

        private IHostingEnvironment _hostingEnv;

        public UploadController(IHostingEnvironment hostingEnv)

        {

            _hostingEnv = hostingEnv;

        }

        [HttpPost]

        public IActionResult Index()

        {

            var file = Request.Form.Files;

            if (file.Sum(f => f.Length) > )

            {

                foreach (var pic in file)

                {

                    var picname = ContentDispositionHeaderValue

                                .Parse(pic.ContentDisposition)

                                .FileName

                                .Trim('"');

                    var exname = picname.Substring(picname.LastIndexOf("."));

                    var picfullname = DateTime.Now.ToString() + exname;

                    picname = _hostingEnv.WebRootPath + $@"\UploadImg\{picfullname}";

                    using (FileStream fs = System.IO.File.Create(picname))

                    {

                        pic.CopyTo(fs);

                        fs.Flush();

                    }

                }

            }

            return Content("ok");

        }

    }

 public class UploadController : Controller

    {

        [HttpPost]

        public ActionResult Index(HttpPostedFileBase picture)

        {

            if (picture.ContentLength > )

            {

                string filePath = Path.Combine(HttpContext.Server.MapPath("../UploadImg"),

                   Path.GetFileName(picture.FileName));

                picture.SaveAs(filePath);

            }

            return Content("ok");

        }

    }

<form method="post" enctype = "multipart/form-data">

 <div class="form-group">

<label class="control-label col-md-2">预览图</label>

<div class="col-md-4">

  <div class="fileupload fileupload-new" data-provides="fileupload">

    <div class="fileupload-new img-thumbnail" style="width: 200px; height: 150px;">

       <img src="~/Images/AAAAAA&amp;text=no+image.png" />

               </div>

      <div class="fileupload-preview fileupload-exists img-thumbnail" style="width: 200px; max-height: 150px"></div>

       <div>

     <span class="btn btn-default btn-file"><span class="fileupload-new">选择图片</span><span class="fileupload-exists">更换</span><input type="file" name="pic" id="picture"></span><a class="btn btn-default fileupload-exists" data-dismiss="fileupload" href="#">清除</a>

      </div>

    </div>

      </div>

 </div>

</form>