下载调用时传入文件的字节数组对象和文件名即可

 /**
     * 下载文件
     * @param response
     * @param bytes 传入字节数组对象
     * @param fileName 文件名
     * @throws Exception
     */
    public static void down(HttpServletResponse response,byte[] bytes,String fileName) {
        try (OutputStream outputStream = response.getOutputStream()) {//java7新特性 在try()语句的括号里声明和初始化资源 会对实现了Closeable的接口会自动关闭
            response.setHeader("Content-disposition", "attachment;filename=" + URLEncoder.encode(fileName, "utf-8"));    
            outputStream.write(bytes);
            outputStream.flush();    
        } catch (IOException e) {
            logger.error("Tool.down:" + e.getMessage());
        }
        
    }