图片上传返回JSON数据，前台弹出下载保存文件框， 文件里面是JSON数据，页面上没显示图片怎么解决

       InputStream stream = file.getInputStream();
        String oldfileName = file.getOriginalFilename();
        String type = oldfileName.split("\\.")[1];// 获取文件类型
        oldfileName = new String(oldfileName.getBytes(), "utf-8");
        String filename = rootPath + sdf.format(new Date())
                + (int) ((Math.random() + 1) * 100000) + "." + type;
        OutputStream bos = new FileOutputStream(request.getServletContext()
                .getRealPath(filename));
        int bytesRead = 0;
        byte[] buffer = new byte[8192];
        while ((bytesRead = stream.read(buffer, 0, 8192)) != -1) {
            bos.write(buffer, 0, bytesRead);
        }

        bos.close();
        // close the stream
        stream.close();

        obj.put("url", filename);
        obj.put("error",0);

    } catch (Exception e) {

        obj.put("error", "1");
        obj.put("message", e.getMessage());
    }
    // 上传操作
   return obj;
}