java - 如何做条件Gson反序列化默认值

Question

想象一下，如果我有以下 JSON

{"game":"football", "people":"elevent"}
{"game":"badminton", "people":"two"}

我的类(class)如下

class Sport {
    String game;
    String people;
}

我可以对 Json 进行反序列化，如下所示

Sport mySport = Gson().fromJson(json, Sport.class);

但是，如果我的 JSON 只是

{"game":"football"}
{"game":"badminton"}

我希望它自动将 people 初始化为“elevent”或“two”，等待第一个字段。有没有办法配置我的 GsonBuilder() 以在反序列化期间自动实现该目标？

Answer 1

您可以创建自定义JsonDeserializer:

public class SportDeserializer implements JsonDeserializer<Sport> {
    @Override
    public Sport deserialize(final JsonElement json, final Type typeOfT, final JsonDeserializationContext context) throws JsonParseException {
        JsonObject jsonObject = (JsonObject) json;

        String game = jsonObject.get("game").getAsString();
        JsonElement nullablePeople = jsonObject.get("people");
        String people = nullablePeople == null ? null : nullablePeople.getAsString();

        if (people == null || people.isEmpty()) {
            if (game.equals("football")) {
                people = "elevent";
            }
            else if (game.equals("badminton")) {
                people = "two";
            }
        }

        Sport sport = new Sport();
        sport.game = game;
        sport.people = people;

        return sport;
    }
}

然后使用自定义的JsonDeserializer:

GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapter(Sport.class, new SportDeserializer());
Gson gson = gsonBuilder.create();
Sport sport = gson.fromJson(jsonString, Sport.class);