给前段返回文件工具

    public static ResponseEntity<FileSystemResource> export(File file) {
        if (file == null) {
            return null;
        }
        HttpHeaders headers = new HttpHeaders();
        headers.add("Cache-Control", "no-cache, no-store, must-revalidate");
        headers.add("Content-Disposition", "attachment; filename=" + System.currentTimeMillis() + ".xls");
        headers.add("Pragma", "no-cache");
        headers.add("Expires", "0");
        headers.add("Last-Modified", new Date().toString());
        headers.add("ETag", String.valueOf(System.currentTimeMillis()));
        return ResponseEntity
                .ok()
                .headers(headers)
                .contentLength(file.length())
                .contentType(MediaType.parseMediaType("application/octet-stream"))
                .body(new FileSystemResource(file));
    }

    /**
     * 下载文件
     *
     * @param request  /
     * @param response /
     * @param file     /
     */
    public static void downloadFile(HttpServletRequest request, HttpServletResponse response, File file, boolean deleteOnExit) {
        response.setCharacterEncoding(request.getCharacterEncoding());
        response.setContentType("application/octet-stream");
        FileInputStream fis = null;
        try {
            fis = new FileInputStream(file);
            response.setHeader("Content-Disposition", "attachment; filename=" + file.getName());
            IOUtils.copy(fis, response.getOutputStream());
            response.flushBuffer();
        } catch (Exception e) {
            log.error(e.getMessage(), e);
        } finally {
            if (fis != null) {
                try {
                    fis.close();
                    if (deleteOnExit) {
                        file.deleteOnExit();
                    }
                } catch (IOException e) {
                    log.error(e.getMessage(), e);
                }
            }
        }
    }