1、获取要下载文件的ID

    function btn_downfile() {
        var rows = $("#gridTable").datagrid('getChecked');
        if (rows.length == 0) {
            dialogMsg("至少勾选一条数据", 1);
            return false;
        }
        var fileIds = "";
        for (var i = 0; i < rows.length; i++) {
            fileIds += rows[i]["AttachmentID"] + ",";
        }
        fileIds = fileIds.substr(0, fileIds.length - 1);
        $("#formexcel").remove();
        var $form = $("<form id='formexcel' method='post' action='/HR/Employee/DownDocumentFile' style='display:none;'>");
        var $input = $("<input type='hidden' name='FileIds' value='" + fileIds + "'>");
        $("body").append($form);
        $form.append($input);
        $form.submit();
    }

2、根据文件ID获取文件的请求地址

		/// <summary>
        /// 文件打包下载
        /// </summary>
        /// <param name="EmpNo">工号</param>
        /// <param name="FileIds">文件ID</param>
        /// <returns></returns>
        [HttpPost]
        public ActionResult DownDocumentFile(string EmpNo, string FileIds)
        {
            if (string.IsNullOrEmpty(FileIds))
            {
                return Error("请勾选数据！");
            }
            if (string.IsNullOrEmpty(EmpNo))
            {
                EmpNo = "file";
            }
            AttachmentBiz attBiz = new AttachmentBiz();
            var fileList = attBiz.GetListEntity(FileIds);//根据文件ID获取文件地址数据
            if (fileList.Count > 0)
            {
                var streamList= GetFileStreamList(fileList);
                //zip 文件名称
                var zipFileName = EmpNo + "_" + DateTime.Now.ToString("yyyyMMddHHmmss") + ".zip";
                MemoryStream ms = new MemoryStream();
                byte[] buffer;
                using (ZipFile file = ZipFile.Create(ms))
                {
                    file.BeginUpdate();
                    foreach (var item in streamList)
                    {
                        StreamDataSource sd = new StreamDataSource(item.FileStream);
                        file.Add(sd, item.Name);
                    }
                    file.CommitUpdate();
                    buffer = new byte[ms.Length];
                    ms.Position = 0;
                    ms.Read(buffer, 0, buffer.Length);

                }
                return File(ms.ToArray(), "application/zip", zipFileName);
            }
            else
            {
                throw new Exception("文件不能为空！");
            }
        }

3、通过请求文件地址获取文件流

		/// <summary>
        /// 获取文件流
        /// </summary>
        /// <param name="list"></param>
        private List<DownloadModel> GetFileStreamList(List<AttachmentEntity> list)
        {
            try
            {
                EmployeeBiz employeeBiz = new EmployeeBiz();
                var empList = employeeBiz.GetAllEmployeeList();//获取用户数据
                List<DownloadModel> downloadList = new List<DownloadModel>();
                foreach (var item in list)
                {
                    var empentity = empList.Where(x => x.UserID == item.DocumentID).First();
                    string filename = item.AttachmentType + "_" + empentity.EmployeeNo + "_" + empentity.FullNameCN + "_" + item.Title;
                    WebRequest req = WebRequest.Create(item.Url);
                    req.Method = "GET";
                    //读取到内存
                    MemoryStream stmMemory = new MemoryStream();
                    using (WebResponse webRes = req.GetResponse())
                    {
                        int length = (int)webRes.ContentLength;
                        HttpWebResponse response = webRes as HttpWebResponse;
                        Stream stream = response.GetResponseStream();
                        byte[] buffer = new byte[length];
                        int i;
                        //将字节逐个放入到Byte中
                        while ((i = stream.Read(buffer, 0, buffer.Length)) > 0)
                        {
                            stmMemory.Write(buffer, 0, i);
                        }
                    }
                    DownloadModel downloadModel = new DownloadModel();
                    downloadModel.ID = Guid.NewGuid().ToString();
                    downloadModel.Name = filename;
                    downloadModel.FileStream = stmMemory;
                    downloadList.Add(downloadModel);
                }
                return downloadList;
            }
            catch (System.Exception ex)
            {
                throw ex;
            }
        }