RuntimeTypeAdapterFactory를 사용하여 Gson으로 다형성 개체 목록을 직렬화하는 방법은 무엇입니까?

<code class="java">RuntimeTypeAdapterFactory<ObixBaseObj> adapter = 
        RuntimeTypeAdapterFactory
                .of(ObixBaseObj.class)
                .registerSubtype(ObixBaseObj.class)
                .registerSubtype(ObixOp.class);

Gson gson2=new GsonBuilder().setPrettyPrinting().registerTypeAdapterFactory(adapter).create();
System.out.println(gson2.toJson(lobbyObj));</code>

<code class="java">public class ObixBaseObj {
    // ...
    private static final RuntimeTypeAdapterFactory<ObixBaseObj> adapter = 
            RuntimeTypeAdapterFactory.of(ObixBaseObj.class);

    public static void registerType(
            RuntimeTypeAdapterFactory<?> adapter) {
        GsonUtils.registerType(adapter);
    }

    // ...
}

public class ObixOp extends ObixBaseObj {
    // ...
    public ObixOp() {
        super();
        obix = "op";
    }

    // ...
}</code>

<code class="java">public class GsonUtils {
    private static final GsonBuilder gsonBuilder = new GsonBuilder()
            .setPrettyPrinting();

    public static void registerType(
            RuntimeTypeAdapterFactory<?> adapter) {
        gsonBuilder.registerTypeAdapterFactory(adapter);
    }

    public static Gson getGson() {
        return gsonBuilder.create();
    }
}</code>

<code class="java">ObixBaseObj lobbyObj = new ObixBaseObj();
lobbyObj.setIs("obix:Lobby");

ObixOp batchOp = new ObixOp();
batchOp.setName("batch");
batchOp.setIn("obix:BatchIn");
batchOp.setOut("obix:BatchOut");

lobbyObj.addChild(batchOp);

Gson gson = GsonUtils.getGson();
System.out.println(gson.toJson(lobbyObj));</code>