How to serialize Date to long using gson?

Question

I recently switched some of our serialization from Jackson to Gson. Found out that Jackson serializes dates to longs.

But, Gson serializes Date

Answer 1

First type adapter does the deserialization and the second one the serialization.

Gson gson = new GsonBuilder()
        .registerTypeAdapter(Date.class, (JsonDeserializer) (json, typeOfT, context) -> new Date(json.getAsJsonPrimitive().getAsLong()))
        .registerTypeAdapter(Date.class, (JsonSerializer) (date, type, jsonSerializationContext) -> new JsonPrimitive(date.getTime()))
        .create();

Usage:

String jsonString = gson.toJson(objectWithDate1);
ClassWithDate objectWithDate2 = gson.fromJson(jsonString, ClassWithDate.class);
assert objectWithDate1.equals(objectWithDate2);