ByteArrayOutputStream out = new ByteArrayOutputStream();
        File outputFile = new File(templateName + ".xlsx");
        OutputStream fileOutputStream = new FileOutputStream(outputFile);
        SimpleXlsxReportConfiguration configuration = new SimpleXlsxReportConfiguration();
        configuration.setOnePagePerSheet(true);
        configuration.setIgnoreGraphics(false);
        Exporter exporter = new JRXlsxExporter();
        exporter.setExporterInput(new SimpleExporterInput(print));
        exporter.setExporterOutput(new SimpleOutputStreamExporterOutput(out));
        exporter.setConfiguration(configuration);
        exporter.exportReport();
        out.writeTo(fileOutputStream);
        return out.toByteArray();

String content = new String(file); // file - это то, что я получаю из сервиса
res.setContentType("text/html");
res.setCharacterEncoding("UTF-8");
OutputStream out = res.getOutputStream();
out.write(content.getBytes("UTF-8"));
out.flush();
out.close();

    let xhr = new XMLHttpRequest();
    xhr.open("POST", url, true);
    xhr.setRequestHeader('Content-type','application/json; charset=utf-8');
    xhr.onload = function () {// здесь я получаю ответ от контроллера, в данном случае - html файл
        $("#report-content").html(xhr.responseText);
    }

    @PostMapping(value = "getReportXlsx")
    public ResponseEntity<Resource> getReportXlsx(@RequestBody MainRequest<WebReportRequestDTO> request) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException, IOException {
        WebReportRequestDTO req = request.getRequest();
        ReportExcelDataDTO report = webReportService.createReportFile(req.getParams(), req.getTemplateName());
        byte[] reportData = report.getOut();
        ByteArrayResource resource = new ByteArrayResource(reportData);
        return ResponseEntity.ok()
                .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + URLEncoder.encode(report.getFileName(), charset ) + "\"")
                .contentLength(reportData.length)
                .contentType(MediaType.parseMediaType("application/octet-stream; charset=" + charset))
                .body(resource);

 public ReportExcelDataDTO createReportFile(List<WebReportParamsDTO> params, String templateName) throws IOException, ParseException, JRException {
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        File outputFile = new File(templateName + ".xlsx");
        OutputStream fileOutputStream = new FileOutputStream(outputFile);
        SimpleXlsxReportConfiguration configuration = new SimpleXlsxReportConfiguration();
        configuration.setOnePagePerSheet(true);
        configuration.setIgnoreGraphics(false);
        Exporter exporter = new JRXlsxExporter();
        exporter.setExporterInput(new SimpleExporterInput(getSalesDebetCardMkbReportPrint(params, templateName)));
        exporter.setExporterOutput(new SimpleOutputStreamExporterOutput(out));
        exporter.setConfiguration(configuration);
        exporter.exportReport();
        out.writeTo(fileOutputStream);
        ReportExcelDataDTO result = new ReportExcelDataDTO();
        result.setFileName(templateName + ".xlsx");
        result.setOut(out.toByteArray());
        return result;
    }

let xhr = new XMLHttpRequest();
    xhr.open("POST", url, true);
    xhr.setRequestHeader('Content-type','application/json; charset=utf-8');
    xhr.onload = function () {
        console.log(xhr.response);
    }
    xhr.send(getJSONParams());