FireFox的上传请求bug，一次提交，请求两次，其中一次是get.

   public void execute(Context context, @Param("mapdata") FileItem mapdata) throws IOException {
        brc.setBuffering(false);
        ResponseMsg rm = new ResponseMsg();
        try {
            byte[] imgData = mapdata.get();
            //...................省略
            g.drawString("Total: " + list.size(), 10, 20);
            response.setContentType("image/jpeg");
            OutputStream out = response.getOutputStream();
            JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
            encoder.encode(tagImg);
            out.flush();

        } catch (Exception e) {
            logger.error(e.getMessage());
            rm.setCode(RESPONSECODE.ERR);
            rm.setMsg(e.getMessage());
            response.reset();
            sendMsg(response, JSON.toJSONString(rm));
        }
    }