Gson不能反序列化继承类吗？

Question

我有一个简单的Json结构,如:

{"MessageType":"TimeData","TimeData":{"hh":12,"mm":13,"ms":15,"ss":14}}

我设计了以下类来反序列化它:

public class JsonMessage
{
    public enum MessageTypes{
        WhoAreYou,
        TimeData
    }
    JsonMessage(){
    }
    public MessageTypes MessageType;
}

class TimeData extends JsonMessage{
    int hh;
    int mm;
    int ss;
    int ms;

    TimeData() {
    }    
}

我需要将反序列化分为两个阶段:

1-反序列化阅读MessageType.

2-继续基于的反序列化 MessageType

代码很简单:

public void dispatch(Object message, IoSession session)
    {

            Gson gson = new Gson();
            JsonMessage result = gson.fromJson(message.toString(), JsonMessage.class);
            System.out.println(result.MessageType.toString());
            switch (result.MessageType)
                {
                    case WhoAreYou:{
                    //.....
                    break;
                    }
                    case TimeUpdate:
                        TimeData res = new Gson().fromJson(message.toString(), TimeData.class);
                        System.out.println(res.hh);
                        break;
                    default:break;
        }
    }

我的程序可以输入正确的switch-case(这是TimeUpdate)但它没有正确解析它(println打印0而不是12)

你认为我做错了什么？谢谢

Answer 1

问题是,当您的Java只是一个对象时,您的JSON代表一个包含您感兴趣的另一个对象的Object.

实际上,您可以为每种类型编写反序列化器,并在确定后使用它们MessageType:

public static void main(String[] args)
{
    Gson gson = new GsonBuilder().registerTypeAdapter(TimeData.class, new TimeDataDeserializer()).create();
    String json = "{\"MessageType\":\"TimeData\",\"TimeData\":{\"hh\":12,\"mm\":13,\"ms\":15,\"ss\":14}}";
    JsonMessage message = gson.fromJson(json, JsonMessage.class);

    switch(message.MessageType)
    {
        case TimeData:
            TimeData td = new GsonBuilder()
                            .registerTypeAdapter(TimeData.class, new TimeDataDeserializer())
                            .create()
                            .fromJson(json, TimeData.class);
            td.MessageType = message.MessageType
            System.out.println(td.hh);
            break;
        default:
            break;
    }
}

class TimeDataDeserializer implements JsonDeserializer<TimeData>
{
    @Override
    public TimeData deserialize(JsonElement je, Type type, JsonDeserializationContext jdc)  
        throws JsonParseException
    {
        JsonObject jo = je.getAsJsonObject().getAsJsonObject("TimeData");
        Gson g = new Gson();
        return g.fromJson(jo, TimeData.class);
    }
}