下载文件的代码为：

response.setContentType("text/html; charset=UTF-8");
        response.setCharacterEncoding("UTF-8");
        FileInputStream fis = null;
        BufferedInputStream buff = null;
        OutputStream myout = null;
        File file = new File(download_file_path + uuid, filename);
        try {
            if (!file.exists()) {
                response.sendError(404, "File not found!!");
                return "";
            } else {
                response.setContentType("APPLICATION/OCTET-STREAM");
                response.setContentLength((int) file.length());
                response.setHeader("Content-Disposition", "attachment;filename=" + filename);
            }
            fis = new FileInputStream(file);
            buff = new BufferedInputStream(fis);
            byte[] b = new byte[1024];
            long k = 0;
            myout = response.getOutputStream();
            while (k < file.length()) {
                int j = buff.read(b, 0, 1024);
                k += j;
                myout.write(b, 0, j);
            }
            myout.flush();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (fis != null) {
                    fis.close();
                }
                if (buff != null)
                    buff.close();
                if (myout != null)
                    myout.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }