Java 通过网络流转发文件到浏览器

public void downloadVideoById(HttpServletRequest request, HttpServletResponse response) throws Exception {
        logger.info("下载请求start>>");
        String fileName = request.getParameter("fileName");//文件名
        String filePath = request.getParameter("filePath");//文件名
        try {
            if (StringUtil.isEmpty(fileName) || StringUtil.isEmpty(filePath)) {
                response.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
                response.setCharacterEncoding("UTF-8");
                response.setContentType("application/json;charset=UTF-8");
                response.getWriter().print("参数错误，请联系管理员!");
                response.flushBuffer();
                return;
            }

            URL pathUrl = new URL(filePath);
            HttpURLConnection urlcon = (HttpURLConnection) pathUrl.openConnection();
            if(urlcon.getResponseCode()>=400){
                response.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
                response.setCharacterEncoding("UTF-8");
                response.setContentType("application/json;charset=UTF-8");
                response.getWriter().print("文件不存在，请联系管理员!");
                response.flushBuffer();
                return;
            }
            //获取输入流对象（用于读文件） 网络流
            InputStream inputStream = new URL(filePath).openStream();
            //本地流文件
            // FileInputStream fis = new FileInputStream(new File(filePath));
            //动态设置响应类型，根据前台传递文件类型设置响应类型
            response.setContentType("application/" + fileName.substring(fileName.lastIndexOf(".")+1));
            //设置响应头,attachment表示以附件的形式下载，inline表示在线打开
            response.setHeader("content-disposition", "attachment;fileName=" + URLEncoder.encode(fileName, "UTF-8"));//下载时浏览器显示的名称
            //获取输出流对象（用于写文件）
            ServletOutputStream os = response.getOutputStream();
            //下载文件,使用spring框架中的FileCopyUtils工具
            FileCopyUtils.copy(inputStream, os);

        } catch (Exception e) {
            logger.error("下载失败 start >>",e);
            response.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
            response.setCharacterEncoding("UTF-8");
            response.setContentType("application/json;charset=UTF-8");
            response.getWriter().print("下载失败，请联系管理员!");
            response.flushBuffer();
        }


    }