To be clear, let introduse some model:
interface A { boolean isSomeCase(); } class AAdapter implements JsonSerializer<A> { public JsonElement serialize(A src, Type typeOfSrc, JsonSerializationContext context) { if (src.isSomeCase()) { /* some logic */ return result; } else { JsonObject json = new JsonObject(); JsonElement valueJson = <???>; // TODO serialize src like POJO json.add(src.getClass().getSimpleName(), valueJson); return json; } } } Gson gson = new GsonBuilder() .registerTypeHierarchyAdapter(A.class. new AAdapter()) .create();
How it is possible to serealize some instance of A, which isSomeCase() = false, like any other object, that is serialized by ReflectiveTypeAdapterFactory.Adapter.
You can write a custom TypeAdapterFactory and handle incoming object's isSomeCase() result in its TypeAdapter's write() method and apply your logic there:
public class ATypeAdapterFactory implements TypeAdapterFactory { public TypeAdapter<A> create(Gson gson, TypeToken type) { if (!A.class.isAssignableFrom(type.getRawType())) { // Check if incoming raw type is an instance of A interface return null; } final TypeAdapter<A> delegate = gson.getDelegateAdapter(this, type); return new TypeAdapter<A>() { @Override public void write(JsonWriter out, A value) throws IOException { if(value.isSomeCase()) { // your custom logic here out.beginObject(); out.name("x").value(0); out.endObject(); } else { // default serialization here delegate.write(out, value); } } @Override public A read(JsonReader in) throws IOException { return delegate.read(in); } }; } }
Test:
final GsonBuilder gsonBuilder = new GsonBuilder(); // Register custom type adapter factory gsonBuilder.registerTypeAdapterFactory(new ATypeAdapterFactory()); final Gson gson = gsonBuilder.create(); A aSomeCaseTrue = new AImpl(true); System.out.print("aSomeCaseTrue:" + gson.toJson(aSomeCaseTrue)); // writes; aSomeCaseTrue:{"x":0} A aSomeCaseFalse = new AImpl(false); System.out.print("aSomeCaseFalse:" + gson.toJson(aSomeCaseFalse);); // writes; aSomeCaseFalse:{"someCase":false}
Extras:
1) Your interface:
interface A { boolean isSomeCase(); }
2) A sample class which implements your sample interface:
class AImpl implements A { boolean someCase; public AImpl(boolean value) { this.someCase = value; } @Override public boolean isSomeCase() { return someCase; } }
