在SpringBoot项目中，如果我们想要下载多个文件，可以考虑将文件打成zip压缩包，通过ZipOutputStream流的方式进行下载，不保存压缩后的文件。

下面是工具类 ZipFileUtils 代码：

public class ZipFileUtils {

    /**
     * web下载打成压缩包的文件--流方式
     *
     * @param response 响应
     * @param fileList 文件列表
     * @param zipName  压缩包名
     */
    public static void downloadZipFiles(HttpServletResponse response, List<String> fileList, String zipName) {
        ZipOutputStream zipOutputStream = null;
        try {
            //设置响应头
            response.reset();
            response.setContentType("application/octet-stream");
            response.setCharacterEncoding("utf-8");
            //设置文件名称
            response.setHeader("Content-Disposition", "attachment;filename=" + zipName);
            zipOutputStream = new ZipOutputStream(response.getOutputStream());
            for (String file : fileList) {
                toZip(zipOutputStream, new File(file));
            }
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        } finally {
            //关闭资源
            if (null != zipOutputStream) {
                try {
                    zipOutputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * 压缩文件
     *
     * @param zipOutputStream 压缩文件流
     * @param file            待压缩文件
     */
    private static void toZip(ZipOutputStream zipOutputStream, File file) {
        String filename = file.getName();
        BufferedInputStream bis = null;
        try {
            bis = new BufferedInputStream(Files.newInputStream(file.toPath()));
            //设置压缩包内文件的名称
            zipOutputStream.putNextEntry(new ZipEntry(filename));
            int size;
            byte[] buffer = new byte[4096];
            while ((size = bis.read(buffer)) > 0) {
                zipOutputStream.write(buffer, 0, size);
            }
            zipOutputStream.closeEntry();
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        } finally {
            //关闭资源
            if (null != bis) {
                try {
                    bis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

Controller使用示例：

    @GetMapping("/testZip")
    public void testZip(HttpServletResponse response) {
        ArrayList<String> fileList = new ArrayList<>();
        //文件路径
        fileList.add("././license/key/private.key");
        fileList.add("././license/key/public.key");
        ZipFileUtils.downloadZipFiles(response,fileList,"test.zip");
    }