SerializeConfig config = new SerializeConfig(true); // singleton
ParserConfig parserConfig = new ParserConfig(true); // singleton

public static class Model {
    private int id;
}

Model model = new Model();
model.id = 123;
assertEquals("{\"id\":123}", JSON.toJSONString(model, config));

Model model2 = JSON.parseObject("{\"id\":123}", Model.class, parserConfig);
assertEquals(model.id, model2.id);