Bagaimana untuk Membuat Deserializer JSON Tersuai untuk Gson?

public class User {
    int id;
    String name;
    Timestamp updateDate;
}

[{"id":1,"name":"Jonas","update_date":"1300962900226"},
{"id":5,"name":"Test","date_date":"1304782298024"}]

import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import java.lang.reflect.Type;
import java.sql.Timestamp;

public class UserDeserializer implements JsonDeserializer<User> {
    @Override
    public User deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
        throws JsonParseException {
        long time = json.getAsJsonPrimitive().getAsLong();
        return new User(
            json.get("id").getAsInt(),
            json.get("name").getAsString(),
            new Timestamp(time));
    }
}

GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapter(User.class, new UserDeserializer());
Gson gson = gsonBuilder.create();