public class GsonVsJackson {


    public static void main(String[] args) throws Exception {
        testGson();
        System.out.println("========================");
        testJackson();
    }

    public static void testGson() {
        System.out.println("Testing Gson 2.8");
        Gson gson = new Gson();
        HashMap<String, Object> newTest = new HashMap<>();
        newTest.put("first", 6906764140092371368L);
        String jsonString = gson.toJson(newTest);
        System.out.println(jsonString); // output ok: {"first":6906764140092371368}
        Map<String, Object> mapFromJson = gson.fromJson(jsonString, Map.class);
        Number numberFromJson = (Number) mapFromJson.get("first");
        System.out.println(numberFromJson.getClass() + " = " + numberFromJson); // java.lang.Double val 6.9067641400923709E18
        long longVal = numberFromJson.longValue();
        System.out.println(longVal); // output rounded: 6906764140092370944
    }

    public static void testJackson() throws Exception {
        System.out.println("Testing Jackson");
        ObjectMapper jackson = new ObjectMapper();
        HashMap<String, Object> newTest = new HashMap<>();
        newTest.put("first", 6906764140092371368L);
        String jsonString = jackson.writeValueAsString(newTest);
        System.out.println(jsonString); // output ok: {"first":6906764140092371368}
        Map<String, Object> mapFromJson = jackson.readValue(jsonString, Map.class);
        Number numberFromJson = (Number) mapFromJson.get("first");
        System.out.println(numberFromJson.getClass() + " = " + numberFromJson); // java.math.BigInteger = 6906764140092371368
        long longVal = numberFromJson.longValue();
        System.out.println(longVal); // output OK: 6906764140092371368
    }

}