Api.java

public interface Api {

    String API_BASE_URL = "http://your.domain.here";

    class Factory {

        public static <S> S create(Class<S> service) {

            OkHttpClient.Builder httpClient = new OkHttpClient.Builder();

            //JacksonConverterFactory adding  TaskDeserializer to SimpleModule
            SimpleModule module = new SimpleModule();
            module.addDeserializer(TaskDeserializer.class, new TaskDeserializer());

            ObjectMapper objectMapper = new ObjectMapper();
            objectMapper.registerModule(module);

            Retrofit.Builder builder =
                    new Retrofit.Builder()
                            .baseUrl(API_BASE_URL)
                            .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                            .addConverterFactory(JacksonConverterFactory.create(objectMapper));

            Retrofit retrofit = builder.client(httpClient.build())
                    .build();

            return retrofit.create(service);
        }
    }
}