两种方式 都是可以直接触发浏览器下载并显示进度条的
前提是用 超链接的方式，不能用ajax

1，利用StreamingResponseBody + ResponseEntity

    @GetMapping("/export1")
    public ResponseEntity<StreamingResponseBody> exportData1() throws IOException {
        File file = new File("D:\\Downloads\\Xshell-7.0.0164p.exe");
        InputStream inputStream = Files.newInputStream(file.toPath());

        StreamingResponseBody stream = outputStream -> {

            int numberOfBytesToWrite;
            byte[] data = new byte[64 * 1024];
            while ((numberOfBytesToWrite = inputStream.read(data, 0, data.length)) != -1) {
                outputStream.write(data, 0, numberOfBytesToWrite);
            }
            inputStream.close();
        };

        String filename = URLEncoder.encode(file.getName(), StandardCharsets.UTF_8);
        // 处理空格 文件名里的空格会变成+号
        filename = filename.replaceAll("\\+", "%20");
        System.out.println("filename:"+filename);
        return ResponseEntity.ok()
                .contentType(MediaType.APPLICATION_OCTET_STREAM)
                .contentLength(file.length())
                .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=" + filename + ";filename*=UTF_8''"+filename)
                .body(stream);
    }

2，FileCopyUtils（spring 自带的工具类） + HttpServletResponse

    @GetMapping("/export2")
    public static void exportData2(HttpServletResponse response) {
        File file = new File("D:\\Downloads\\Xshell-7.0.0164p.exe");
        try (InputStream inputStream = Files.newInputStream(file.toPath())) {
            response.setContentType("application/octet-stream");
            response.reset();

            String filename = URLEncoder.encode(file.getName(), StandardCharsets.UTF_8);
            // 处理空格 文件名里的空格会变成+号
            filename = filename.replaceAll("\\+", "%20");

            response.addHeader("Content-Disposition", "attachment;filename=" + filename);
            response.addHeader("Content-Length", "" + file.length());


            InputStream fis = new BufferedInputStream(inputStream);
            OutputStream toClient = new BufferedOutputStream(response.getOutputStream());

            FileCopyUtils.copy(fis, toClient);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

前端就这样，与下载静态资源一样

<a href="/export1">下载</a>

3，如果想用ajax的方式，要自己处理进度条

3.1 jquery 不支持

3.2 原生的xhr 支持

const request = (options = {}) => {
    const { url, method, data } = options;
    return new Promise((resolve) => {
        const xhr = new XMLHttpRequest();
        xhr.addEventListener('readystatechange', () => {
            if (xhr.readyState === xhr.DONE) {
                resolve(xhr.responseText);
            }
        })
        // 提交数据的进度
        xhr.upload.addEventListener('progress', (e) => {
            // 当前上传的字节长度，总的字节长度
            console.log(e.loaded, e.total);
        })
        // 接受数据的进度
        xhr.addEventListener('progress', (e) => {
            // 当前接受的字节长度，总的字节长度
            console.log(e.loaded, e.total);
        })
        xhr.open(method, url);
        xhr.send(data);
    })
}

3.3 fech（只能监听数据的下载进度）

const request = (options = {}) => {
    const { url, method, data } = options;
    return new Promise(async (resolve) => {
        const resp = await fetch(url, {
            body: data
        })
        const total = resp.headers.get('content-length');
        const decoder = new TextDecoder();
        let body = '';
        const reader = resp.body?.getReader();
        let loaded = 0;
        while (1) {
            const { done, value } = await reader?.read();
            if (done) {
                break;
            }
            loaded += value.length;
            body += decoder.decode(value);
            // 数据的总长度，当前接受的长度
            console.log(loaded, total)
        }
        resolve(body)
    })
}

3.4 axios

    const request = (options = {}) => {
    const { url, method, data } = options;
    const instance = axios.create({baseURL:'http://127.0.0.1:8887'})
    return new Promise(async (resolve) => {
        const res = await instance.get('/dubbodemo/tc1/export2', {
            responseType: 'blob',
            onDownloadProgress: e => {          
                const total = e.total
                const loaded = e.loaded
                // 数据的总长度，当前接受的长度
                console.log(loaded, total)
            },
            // `onUploadProgress` 允许为上传处理进度事件
            onUploadProgress: function (progressEvent) {
            // 处理原生进度事件
            },
        })
        
        resolve(res.data)
    })
}

Disposition 说明：https://blog.csdn.net/m0_46672781/article/details/143159880