"date": {
    "type": "date",
    "format": "yyyy-MM-dd'T'HH:mm:ss.SSSZ"
}

client.prepareIndex(INDEX, TYPE, id))
        .setSource(gson.toJson(object), XContentType.JSON)
        .setRefreshPolicy(RefreshPolicy.IMMEDIATE)
        .get();

public class ZonedDateTimeAdapter implements JsonSerializer<ZonedDateTime> {

    public JsonElement serialize(ZonedDateTime date, Type typeOfSrc, JsonSerializationContext context) {
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSSZ");
        return new JsonPrimitive(date.format(formatter));
    }

}