java代码转发文件流，前端下载文件流

后端文件流转发代码
public static void doGetFile(HttpServletResponse httpResponse,String url) {
        CloseableHttpClient httpClient = null;
        CloseableHttpResponse response = null;
        byte[] result = null;
        try {
            // 通过址默认配置创建一个httpClient实例
            httpClient = HttpClients.createDefault();
            HttpGet httpGet = new HttpGet(url);
            // 设置请求头信息，鉴权
            //httpGet.setHeader("Authorization", "Bearer da3efcbf-0845-4fe3-8aba-ee040be542c0");
            // 设置配置请求参数
            RequestConfig requestConfig = RequestConfig.custom().setConnectTimeout(35000)// 连接主机服务超时时间
                    .setConnectionRequestTimeout(35000)// 请求超时时间
                    .setSocketTimeout(60000)// 数据读取超时时间
                    .build();
            if (summaryVer != null) {
                httpGet.setHeader("sd-summary-ver", summaryVer);
                httpGet.setHeader("sd-summary", summary);
            }
            // 为httpGet实例设置配置
            httpGet.setConfig(requestConfig);
            // 执行get请求得到返回对象
            response = httpClient.execute(httpGet);
            // 通过返回对象获取返回数据
            HttpEntity entity = response.getEntity();
            InputStream content = entity.getContent();
            byte[] buffer = new byte[1024*4];
            int n = 0;
            ServletOutputStream outputStream = httpResponse.getOutputStream();
            while (-1 != (n = content.read(buffer))) {
                outputStream.write(buffer, 0, n);
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 关闭资源
            if (null != response) {
                try {
                    response.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (null != httpClient) {
                try {
                    httpClient.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

前端代码
function downloadFile() {

const xhr = new XMLHttpRequest();
xhr.open('POST', 'url(下载接口地址)', true);
xhr.responseType = "blob";
xhr.onload = () => {
    openProgressBar("close", true, "下载");
    const blob = xhr.response;
    const blobUrl = URL.createObjectURL(blob);
    const a = document.createElement('a');
    a.style.display = 'none';
    a.download="数据列表.xls"
    a.href = blobUrl;
    a.target = '_blank';
    a.click();
}
var params2 = {"flowType":3,"pageNum":1,"pageSize":10}
xhr.setRequestHeader("Content-Type","application/json;charset=UTF-8");
xhr.send(JSON.stringify(params2));
}