ElementalJsonDeserializer.java

public class ElementalJsonDeserializer extends JsonDeserializer<JsonValue> {

    @Override
    protected JsonValue doDeserialize(JsonReader reader, JsonDeserializationContext ctx, JsonDeserializerParameters params) {
        if (reader.hasNext()) {
            String nextValue = reader.nextValue();
            JsonValue value = Json.instance().parse(nextValue);
            value = makeCastableToJavaScriptObject(value);
            return value;
        }
        return null;
    }

    static native JsonValue makeCastableToJavaScriptObject(JsonValue value) /*-{
        return Object(value);
    }-*/;
}

ElementalJsonSerializer.java

public class ElementalJsonSerializer extends JsonSerializer<Object> {

    @Override
    protected void doSerialize(JsonWriter writer, Object value, JsonSerializationContext ctx, JsonSerializerParameters params) {
        if (value instanceof JsonValue) {
            JsonValue jsonValue = (JsonValue) value;
            writer.rawValue(jsonValue.toJson());
        } else {
            // If elemental gives us a JS primitive, use JS serialization
            writer.rawValue(stringify(value));
        }
    }

    final public native String stringify(Object value) /*-{
        return $wnd.JSON.stringify(value);
    }-*/;

}