流保存为文件

　　　　　this.http.post(URL, p, {responseType: 'blob'}).then(res => {
          if (res.type === 'application/octet-stream') {
            loading.close();
            var blob = new Blob([res], {type: res.type});
            var downloadUrl = window.URL.createObjectURL(blob);
            var anchor = document.createElement("a");
            anchor.href = downloadUrl;
            // 默认代开乱码是正常的，用户知道自己所需的格式去更改扩展名
            anchor.download = "default.txt";
            anchor.click();
            window.URL.revokeObjectURL(blob);
          } else {
            loading.close();
          }
        });