gistfile1.txt

        Map<String, Object> criteria = new LinkedHashMap<>();
        criteria.put("categories", Arrays.asList("feedhenry"));
        Map<String, Object> jsonContainer = new LinkedHashMap<>();
        jsonContainer.put("alert", "Hello Luke, This is from MQTT");
        jsonContainer.put("criteria", criteria);

        String jsonPayload = new Gson().toJson(jsonContainer);