格式化 JSON 以显示高图表的格式

我正在运行一个servlet，它从doGet上的DB中提取数据，并使用JSON格式的字符串进行响应以填充Highchart.js时间序列图表：

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String json = "";
        String sDate = request.getParameter("start");
        String eDate = request.getParameter("end");
        String app = request.getParameter("app");
        String env = request.getParameter("env");

            if (sDate != null && eDate != null) {
                Timestamp from = TimestampUtils.parseTimestamp(sDate, null);
                Timestamp to = TimestampUtils.parseTimestamp(eDate, null);
                try {
                    throughPutList = interop.getThroughputEntriesInTimespan(env, app, from, to);
                } catch (Exception e) {
                    e.printStackTrace();
                }
                int counter = 1;
                if (throughPutList != null) {
                    json += "[";
                }
                assert throughPutList != null;
                for (ThroughputEntry chartModel : throughPutList) {
                    json += "[" + (chartModel.getRetrieved().getEpochSecond()* TimestampUtils.MILLIS_PER_SECOND + "," + chartModel.getThroughput() +  "]");
                    if (counter < throughPutList.size()) {
                        json += ",";
                    }
                    counter++;
                }
                if (throughPutList != null) {
                    json += "]";
                }
                if (throughPutList == null) {
                    json = "No record found";
                }
            } else {
                json = "Date must be selected." + "App : " + app + " " + eDate;
            }
            response.getWriter().write(json);
        }
}

我是javascript、highchart和JSON的新手，是否可以对其进行优化以使用实际的JSON对象/数组而不是字符串，或者我有合理的方法来解决这个问题。