how can I work with wrapped data using moshi, retrofit and java?

I'm working with an API where all data are wrapped in a custom object (see below), so I cannot use moshi to convert the retrofit body direct to my models. What is the best way to work with moshi in this case?

#COLLECTIONS ENDPOINT

{
    "status": 200,
    "data": [
        {
            "id": 28122,
            "name": "Abandonei",
            "counts": {
                "books": 3
            }
        },
        {
            "id": 21091,
            "name": "Lendo",
            "counts": {
                "books": 6
            }
        },
    ],
    "errors": [],
    "pagination": {
        "after": 2,
        "hasNextPage": true
    }
}

The same json structure is used in all api endpoints, the default fields are:

{
    "status": 200,
    "data": [],
    "errors": [],
    "pagination": {
        "after": 1,
        "hasNextPage": true
    }
}

My Collection model:

public class BookCollection {
    public long id;
    public String name;
    public ArrayList<Book> books;

    public BookCollection(long id, String name) {
        this.id = id;
        this.name = name;
    }
}

To avoid create a parent class to each model, I have implemented a way to use a class that receive a generic type.

To put this to work I've changed the Moshi class to Gson.

My model:

public class BookCollection {
    public long id;
    public String name;
    public ArrayList<Book> books;

    public BookCollection(long id, String name) {
        this.id = id;
        this.name = name;
    }
}

The wrapper class used to unwrap the json data:

public class ApiWrapper<T> {
public final int status;
public final T data;
public final List<ApiError> errors = new ArrayList<>();
public ApiWrapper(int status, T data, List<ApiError> errors) {
this.status = status;
this.data = data;
this.errors.addAll(errors);
}
}

The Errors class, referenced in the class above:

public class ApiError {
public int code;
public String message;
public String error;
}

Usage:

public interface NetAPI {
@GET("me/collections")
Call<ResponseBody> getCollections(@Header("Authorization") String auth);
}
public class CollectionViewModel extends ViewModel {
private final MutableLiveData<List<Collection>> collections = new MutableLiveData<>();
private final MutableLiveData<Boolean> loading = new MutableLiveData<>();
private final MutableLiveData<Boolean> collectionError = new MutableLiveData<>();
private Call<ResponseBody> call;
private void fetchCollections() {
loading.setValue(true);
call = Api.getInstance().getCollections(TOKEN);
call.enqueue(new Callback<ResponseBody>() {
@Override
public void onResponse(Call<ResponseBody> call, Response<ResponseBody> response) {
try {
collectionError.setValue(false);
//THE SECRET
Gson gson = new Gson();
ApiWrapper<List<Collection>> apiResponse = null;
apiResponse = gson.fromJson(response.body().string(), new TypeToken<ApiWrapper<List<Collection>>>(){}.getType());
collections.setValue(apiResponse.data);
loading.setValue(false);
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
public void onFailure(Call<ResponseBody> call, Throwable t) {
Log.e(getClass().getSimpleName(), "Error loading data", t);
collectionError.setValue(true);
loading.setValue(false);
}
});
}
}

At this way I can reuse my ApiWrapper class to any model (Books, Users, Login, etc).

Thanks.

You will need to setup gson/moshi to use your classes that you have created for the json to object mapping. Here is an example of what those java classes would look like. You can use data classes in kotlin as well. For moshi, you will have to create the adapter to help with the json to object mapping.

publci class CollectionResponse {
public int status;
public List<BookCollection> data;
public List<Error> errors;
public Pagination pagination;
}
public class Pagination {
public int after;
public boolean hasNextPage;
}
public class BookCollection {
public long id;
public String name;
public Count counts;
}
public Count {
public int books;
}
public class Error {
}