/**
     * 打包成zip包
     */
    public static void generateZip(OutputStream os, List<File> files) throws Exception {
        ZipOutputStream out = null;
        try {
            byte[] buffer = new byte[1024];
            //生成的ZIP文件名为Demo.zip
            out = new ZipOutputStream(os);
            //需要同时下载的两个文件result.txt ，source.txt
            for (File file : files) {
                FileInputStream fis = new FileInputStream(file);
                out.putNextEntry(new ZipEntry(file.getName()));
                int len;
                //读入需要下载的文件的内容，打包到zip文件
                while ((len = fis.read(buffer)) != -1) {
                    out.write(buffer, 0, len);
                }
                out.flush();
                out.closeEntry();
                fis.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (out != null) {
                out.close();
            }
        }
    }