下载文件（支持移动端）

    @RequestMapping(value = "download",method = RequestMethod.GET)
    public ResponseEntity<byte[]> download(HttpServletResponse response, HttpServletRequest request) throws Exception{

        //预下载文件路径******
        String preDownload_path = "C:/新建文件夹/记事本.txt";

        int index = preDownload_path.lastIndexOf("/");
        //下载后的文件名
        String downloadName = preDownload_path.substring(index+1);
        System.out.println(index);
        System.out.println(downloadName);

        response.setCharacterEncoding("utf-8");
        response.setContentType("application/octet-stream");
        response.setHeader("Content-Disposition", "attachment;fileName="+java.net.URLEncoder.encode("a.txt","UTF-8"));

        InputStream is = null;
        OutputStream os = null;
        try {
            is = new FileInputStream(new File(preDownload_path));
            os = response.getOutputStream();
            byte[] b = new byte[2048];
            int length;
            while ((length = is.read(b)) > 0) {
                os.write(b, 0, length);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            os.close();
            is.close();
        }
        return null;
    }