Custom gson serializer

gistfile1.java

Gson gson = new GsonBuilder().registerTypeAdapter(ObjectId.class,
    new JsonSerializer<ObjectId>()
    {
        public JsonElement serialize(ObjectId t, Type type,
            JsonSerializationContext jsc)
        {
            return new JsonPrimitive(t.toString());
        }
    }).setDateFormat("MMMM dd, yyyy HH:mm:ss").create();