RuntimeTypeAdapterFactory<Base> with JsonDeserializer<Derived> is unsupported

[dbirkman-paloalto]

Hi,

I want the RuntimeTypeAdapterFactory to differentiate between the derived class types and then deserialize the derived instance using a JsonDeserializer.
However, if I register RuntimeTypeAdapterFactory and JsonDeserializer, Gson does not serialize the derived class using the RuntimeTypeAdapterFactory.

Minimal not working example:

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.paloaltonetworks.mag.dms.utils.gson.RuntimeTypeAdapterFactory;

import java.lang.reflect.Type;
import java.util.Arrays;
import java.util.List;

class Base {}
class Derived1 extends Base {}
class Derived2 extends Base {}


class Derived1Deserializer implements JsonDeserializer<Derived1> {
    @Override
    public Derived1 deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        System.out.println("Can customize deserializing Derived1");
        return null;
    }
}

public class Test {
    private List<Base> bases;

    public static void main(String[] args) {
        RuntimeTypeAdapterFactory<Base> baseRuntimeTypeAdapterFactory = RuntimeTypeAdapterFactory.of(Base.class)
                .registerSubtype(Derived1.class)
                .registerSubtype(Derived2.class);

        GsonBuilder gsonBuilder = new GsonBuilder();
        final Gson gson = gsonBuilder
                .registerTypeAdapter(Derived1.class, new Derived1Deserializer())
                .registerTypeAdapterFactory(baseRuntimeTypeAdapterFactory)
                .create();

        Test test = new Test();
        test.bases = Arrays.asList(new Derived1(), new Derived2());

        String json = gson.toJson(test);
        System.out.println(json); 
        gson.fromJson(json, Test.class);
    }
}

The toJson returns
{"bases":[{},{"type":"Derived2"}]}
instead of:
{"bases":[{"type":"Derived1"},{"type":"Derived2"}]}

and of course fromJson fails afterwards with "JsonParseException: cannot deserialize class Base because it does not define a field named type".

TIA,
Dror

[tlf30]

I am seeing the same issue, does anyone know a solution?

[dbirkman-paloalto]

I didn't find any solution except for making my own copy of RuntimeTypeAdapterFactory.java and patching the code like this:

public <R> TypeAdapter<R> create(Gson gson, TypeToken<R> type) {
    if (type.getRawType() != baseType
            // Workaround for https://github.com/google/gson/issues/1570 - START
            && !labelToSubtype.values().contains(type.getRawType())) {
            // Workaround for https://github.com/google/gson/issues/1570 - END
        return null;
    }
...

[Marcono1234]

Does #2032 describe your issue? (edit: it is related)

[Marcono1234]

This issue unfortunately still exists, even with #1787 being merged. For backward compatibility this specific case was not fixed, see #1787 (comment).

As workaround for the specific case described in this issue it might be possible to use RuntimeTypeAdapterFactory.recognizeSubtypes(), which was added by #2160.