Serialize Java 8 LocalDate as yyyy-mm-dd with Gson

Until further notice, I have implemented a custom serializer like so:

class LocalDateAdapter implements JsonSerializer<LocalDate> {

    public JsonElement serialize(LocalDate date, Type typeOfSrc, JsonSerializationContext context) {
        return new JsonPrimitive(date.format(DateTimeFormatter.ISO_LOCAL_DATE)); // "yyyy-mm-dd"
    }
}

It can be installed e.g. like so:

Gson gson = new GsonBuilder()
        .setPrettyPrinting()
        .registerTypeAdapter(LocalDate.class, new LocalDateAdapter())
        .create();

Kotlin version which supports serializing and deserializing:

class LocalDateTypeAdapter : TypeAdapter<LocalDate>() {

    override fun write(out: JsonWriter, value: LocalDate) {
        out.value(DateTimeFormatter.ISO_LOCAL_DATE.format(value))
    }

    override fun read(input: JsonReader): LocalDate = LocalDate.parse(input.nextString())
}

Register with your GsonBuilder. Wrap using nullSafe() for null support:

GsonBuilder().registerTypeAdapter(LocalDate::class.java, LocalDateTypeAdapter().nullSafe())

I use the following, supports read/write and null values:

class LocalDateAdapter extends TypeAdapter<LocalDate> {
    @Override
    public void write(final JsonWriter jsonWriter, final LocalDate localDate) throws IOException {
        if (localDate == null) {
            jsonWriter.nullValue();
        } else {
            jsonWriter.value(localDate.toString());
        }
    }

    @Override
    public LocalDate read(final JsonReader jsonReader) throws IOException {
        if (jsonReader.peek() == JsonToken.NULL) {
            jsonReader.nextNull();
            return null;
        } else {
            return LocalDate.parse(jsonReader.nextString());
        }
    }
}

Registered as @Drux says:

return new GsonBuilder()
        .registerTypeAdapter(LocalDate.class, new LocalDateAdapter())
        .create();

EDIT 2019-04-04 A simpler implementation

private static final class LocalDateAdapter extends TypeAdapter<LocalDate> {
    @Override
    public void write( final JsonWriter jsonWriter, final LocalDate localDate ) throws IOException {
        jsonWriter.value(localDate.toString());
    }

    @Override
    public LocalDate read( final JsonReader jsonReader ) throws IOException {
        return LocalDate.parse(jsonReader.nextString());
    }
}

Which you can add null support to by registering the nullSafe() wrapped version:

new GsonBuilder()
      .registerTypeAdapter(LocalDate.class, new LocalDateAdapter().nullSafe())