//去掉空的children属性
for (int i = 0; i < ja1.size(); i++) {
    var jo1 = (JSONObject) ja1.get(i);
    if (jo1.getJSONArray("children").size() == 0)
        jo1.remove("children");
    if (null != jo1.get("children")) {
        var ja2 = jo1.getJSONArray("children");
        for (int j = 0; j < ja2.size(); j++) {
            var jo2 = (JSONObject) (ja2.get(j));
            if (jo2.getJSONArray("children").size() == 0)
                jo2.remove("children");
        }
    }
}