Ajax异步请求返回文件流eg：导出文件时，直接将导出数据用文件流的形式返回客户端供客户下载

在异步请求中要返回文件流，不能使用JQuery，因为$.ajax,$.post 不支持返回二进制文件流的类型，可以看到下图，dataType只支持xml，json，script，html这几种格式，没有blob类型。所以只能选择使用原生Ajax XMLReques对象进行处理

前端代码

function output() {
            var branchCode = $("#currentBranchCode").val();
            var transDate = $("#currentTransDate").val();
            if (branchCode == "" || transDate == "") {
                layer.msg("暂无记录，无法导出",{ icon: 7,time: 1000 });
                return;
            }
            var fileName = $("table caption").html() + ".xls";//设置下载时候的文件名
            //要请求的Url和携带的参数
            var url = "/SellAnalyze/Export?currentBranchCode=" + branchCode + "&currentTransDate=" + transDate;
            var xhr = new XMLHttpRequest();
            //设置响应类型为blob类型
            xhr.responseType = "blob";
            xhr.onload = function () {
                if (this.status == "200") {
　　　　　　　　　　　　//获取响应文件流　　 var blob = this.response;
                    var aElem = document.getElementById("exportUrl");
　　　　　　　　　　　　//将文件流保存到a标签
                    aElem.href = window.URL.createObjectURL(blob);
                    aElem.download = fileName;
                    aElem.onload = function (e) {
                            window.URL.revokeObjectURL(aElem.href);
                        };
                    $("#exportUrl").removeClass("hidden");
                    layer.confirm(‘文件已导出,立即下载？‘,function (index) {
                        $("#download").click();
                        
                        layer.close(index);
                        });
                }
            }

            xhr.open("post",url,true);
            xhr.send();
        }

后端代码

　　　　 public ActionResult Export(int? currentBranchCode,DateTime currentTransDate)
        {@H_404_125@
            MemoryStream ms = NPOIExcelWrite(datas);
            ms.Seek(0,SeekOrigin.Begin);
            return File(ms,"application/vnd.ms-excel"@H_404_125@);
        }
        
        /// <param name="datas">写入的数据</param>
        /// <returns></returns>
        private MemoryStream NPOIExcelWrite(SellDTO[] datas)
        {
            string[] titles = { "货品类别","货品类别描述","销售额","同比","环比" };
            NPOI.hssf.usermodel.hssfWorkbook book = new NPOI.hssf.usermodel.hssfWorkbook();
            NPOI.SS.usermodel.ISheet sheet = book.CreateSheet("Sheet1");
            NPOI.SS.usermodel.IRow row = sheet.CreateRow(0);
            for (int i = 0; i < titles.Length; i++)
            {
                row.CreateCell(i).SetCellValue(titles[i]);
            }
            for (int i = 0; i < datas.Length; i++)
            {
                row = sheet.CreateRow(i + 1);
                row.CreateCell(0).SetCellValue(datas[i].JewelryType);
                row.CreateCell(1).SetCellValue(datas[i].JewelryTypeDesc);
                row.CreateCell(2).SetCellValue(datas[i].CurrentMonthSaleroom.ToString("F2"));
                row.CreateCell(3).SetCellValue(datas[i].YearOverYear);
                row.CreateCell(4).SetCellValue(datas[i].LinkRelative);
            }

            @H_404_125@MemoryStream ms @H_404_125@= new MemoryStream();
            book.Write(ms);
            ms.Flush();
            book = null;
            return@H_404_125@ ms;
        }

 参考：https://blog.csdn.net/swl979623074/article/details/77855629/

https://www.cnblogs.com/cdemo/p/5225848.html

https://blog.csdn.net/fangchen12312/article/details/55271296