Retrofit and Centralized Error Handling

Issue

Each request to the server may return error_code. I want to handle these error in one place when I was using AsyncTask I had a BaseAsyncTask like that

public abstract class BaseAsyncTask<Params, Progress, Result> extends AsyncTask<Params, Progress, Result> {

    protected Context context;
    private ProgressDialog progressDialog;
    private Result result;

    protected BaseAsyncTask(Context context, ProgressDialog progressDialog) {
        this.context = context;
        this.progressDialog = progressDialog;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected void onPostExecute(Result result) {
        super.onPostExecute(result);
        HttpResponse<ErrorResponse> response = (HttpResponse<ErrorResponse>) result;
     if(response.getData().getErrorCode() != -1) {
                handleErrors(response.getData());
        }else 
            onResult(result);

    }

    private void handleErrors(ErrorResponse errorResponse) {
    }
     public abstract void onResult(Result result);
    }

But, using retrofit each request has its error handling callback:

                    git.getFeed(user,new Callback<gitmodel>() {
                    @Override
                    public void success(gitmodel gitmodel, Response response) {

                    }

                    @Override
                    public void failure(RetrofitError error) {

                    }
                });
            }
        });

How can I handle all errors in one place?

Solution

If you need to get some 'logic' error, then you need some Java logic since it's not a Retrofit feature so basically:

1. Create a Your implementation Callback that implements the Retrofit Callback
2. Create a base object that define the method 'isError'
3. Modify Retrofit RestAdapter in order to get your Callback instead of the Retrofit One
   

MyCallback.java

import android.util.Log;
import retrofit.Callback;
import retrofit.client.Response;

public abstract class MyCallback<T extends MyObject> implements Callback<T> {

    @Override
    public final void success(T o, Response response) {
        if (o.isError()) {
            // [..do something with error]
            handleLogicError(o);
        }
        else {
            handleSuccess(o, response);
        }
    }

    abstract void handleSuccess(T o, Response response);

    void handleLogicError(T o) {
        Log.v("TAG", "Error because userId is " + o.id);
    }
}

MyObject.java (the base class for all your objects you get from Retrofit)

public class MyObject {
    public long id;
    public boolean isError() {
        return id == 1;
    }
}

MyRealObject.java - a class that extends the base object

public class MyRealObject extends MyObject {
    public long userId;
    public String title;
    public String body;
}

RetroInterface.java - the interface used by retrofit you should be familiar with

import retrofit.http.GET;
import retrofit.http.Path;

public interface RetroInterface {

    @GET("/posts/{id}")
    void sendGet(@Path("id") int id, MyCallback<MyRealObject> callback);

}

And finally the piece of code where you use all the logic

RestAdapter adapter = new RestAdapter.Builder()
    .setEndpoint("http://jsonplaceholder.typicode.com")
    .build();

RetroInterface itf = adapter.create(RetroInterface.class);
itf.sendGet(2, new MyCallback<MyRealObject>() {
    @Override
    void handleSuccess(MyRealObject o, Response response) {
        Log.v("TAG", "success");
    }

    @Override
    public void failure(RetrofitError error) {
        Log.v("TAG", "failure");
    }
});

If you copy and paste this code, you'll get an error when you'll execute the itf.sendGet(1, new MyCallback..) and a success for itf.sendGet(2, new MyCallback...)

Answered By - Mimmo Grottoli