@ResponseBody
@RequestMapping("/file")
public void findfile(String fjid, HttpServletResponse response) throws IOException {
    try {
       //獲取檔案存放的路徑
        TFGyFjxx bean = tfGyFjxxService.findByFjid(fjid);
        String url = bean.getFjdz().replace(fjid, bean.getFjmc());
        File file = new File(url);
        String newFileName = bean.getFjmc();
        if (!file.exists()) {
            //如果檔案不存在就跳出
            return;
        }
        InputStream in = new BufferedInputStream(new FileInputStream(file));
        OutputStream out = new BufferedOutputStream(response.getOutputStream());
        response.setContentType("multipart/form-data");
        response.setHeader("Content-Disposition", "attachment;fileName=" + URLEncoder.encode("合成作戰" + newFileName, "UTF-8"));
        response.setContentLength((int) file.length());
        //讀取檔案流
        int len = 0;
        byte[] buffer = new byte[1024 * 10];
        while ((len = in.read(buffer)) != -1) {
            out.write(buffer, 0, len);
        }
        out.flush();
        out.close();
        in.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

後端程式碼是這樣的，前端只要注意別用ajax提交就ok，一般用a標籤或者window.location.href就行