Centralized error handling retrofit 2?

Question

Before retrofit 2, there was a way of handling erros centrally -

new retrofit.RestAdapter.Builder()
        .setEndpoint(apiUrl)
        .setLogLevel(retro         


        

Answer 1

Retrofit 2.0 moved the ErrorHandler and using a new Callback which includes two methods:

/** Successful HTTP response. */
public void onResponse(Response<T> response, Retrofit retrofit)````

/** Invoked when a network or unexpected exception occurred during the HTTP request. */
public void onFailure(Throwable t)

Retrofit2.x will receive all the HTTP response in the onResponse even though the http code is not 2xx or 3xx, here you need to check the response status code in your onResponse method and check if the response success response (normally 2xx or 3xx) and do right logic processing.

I have upgraded retrofit2.x and my solution about centralized error handling is: Creating a abstract class that extends Retrofit.Callback with two methods onSuccess and onFailed, the onFailed is not abstract as I always do the same process when the business logic failed and do the different thing when the request is successful. You can refer the sample code here

then, when you need to send http request, you need to implement the onSuccess method and you can also override the onFailed method in some case, as I mentioned in my project, I process the failed with same way in most case. You can refer the example here which I used retrofit2 to send a post request.

Hope this can help you!

Answer 2

I have used similar solution as Amir proposes but I'm just wondering if this could be made even easier. I tried the following:

public void onResponse(Response<T> response) {
        if (response.isSuccess()) {
            T resp = response.body();
            handleSuccessResponse(resp);

        } else {
            Response<StatusResponse> statusResponse = response.error(response.code(), response.errorBody());
            handleHttpErrorResponse(statusResponse);
        }
    }

This way I would not need to pass Retrofit instance around. However I'm missing something as error body is not successfully parsed to StatusResponse. I'm not sure what this means in practice:

The change in 2.0.0-beta2 which provided the Retrofit instance to the onResponse callback of Callback has been reverted. There are too many edge cases around providing the Retrofit object in order to allow deserialization of the error body. To accommodate this use case, pass around the Retrofit response manually or implement a custom CallAdapter.Factory does so automatically.

2.0.0-beta3

Answer 3

Well, all you have to do is to make a custom CallAdapter with your custom callbacks, for failure cases. The Retrofit repo has a sample showing a custom CallAdapter. You can find it at retrofit/samples.

Here's a sample showing a custom CallAdapter ( NOT applicable to versions prior to 2.2.0 ):

/*
 * Copyright (C) 2015 Square, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.example.retrofit;

import java.io.IOException;
import java.lang.annotation.Annotation;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.concurrent.Executor;
import javax.annotation.Nullable;
import retrofit2.Call;
import retrofit2.CallAdapter;
import retrofit2.Callback;
import retrofit2.converter.gson.GsonConverterFactory;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.http.GET;

/**
 * A sample showing a custom {@link CallAdapter} which adapts the built-in {@link Call} to a custom
 * version whose callback has more granular methods.
 */
public final class ErrorHandlingAdapter {
  /** A callback which offers granular callbacks for various conditions. */
  interface MyCallback<T> {
    /** Called for [200, 300) responses. */
    void success(Response<T> response);
    /** Called for 401 responses. */
    void unauthenticated(Response<?> response);
    /** Called for [400, 500) responses, except 401. */
    void clientError(Response<?> response);
    /** Called for [500, 600) response. */
    void serverError(Response<?> response);
    /** Called for network errors while making the call. */
    void networkError(IOException e);
    /** Called for unexpected errors while making the call. */
    void unexpectedError(Throwable t);
  }

  interface MyCall<T> {
    void cancel();
    void enqueue(MyCallback<T> callback);
    MyCall<T> clone();

    // Left as an exercise for the reader...
    // TODO MyResponse<T> execute() throws MyHttpException;
  }

  public static class ErrorHandlingCallAdapterFactory extends CallAdapter.Factory {
    @Override public @Nullable CallAdapter<?, ?> get(
        Type returnType, Annotation[] annotations, Retrofit retrofit) {
      if (getRawType(returnType) != MyCall.class) {
        return null;
      }
      if (!(returnType instanceof ParameterizedType)) {
        throw new IllegalStateException(
            "MyCall must have generic type (e.g., MyCall<ResponseBody>)");
      }
      Type responseType = getParameterUpperBound(0, (ParameterizedType) returnType);
      Executor callbackExecutor = retrofit.callbackExecutor();
      return new ErrorHandlingCallAdapter<>(responseType, callbackExecutor);
    }

    private static final class ErrorHandlingCallAdapter<R> implements CallAdapter<R, MyCall<R>> {
      private final Type responseType;
      private final Executor callbackExecutor;

      ErrorHandlingCallAdapter(Type responseType, Executor callbackExecutor) {
        this.responseType = responseType;
        this.callbackExecutor = callbackExecutor;
      }

      @Override public Type responseType() {
        return responseType;
      }

      @Override public MyCall<R> adapt(Call<R> call) {
        return new MyCallAdapter<>(call, callbackExecutor);
      }
    }
  }

  /** Adapts a {@link Call} to {@link MyCall}. */
  static class MyCallAdapter<T> implements MyCall<T> {
    private final Call<T> call;
    private final Executor callbackExecutor;

    MyCallAdapter(Call<T> call, Executor callbackExecutor) {
      this.call = call;
      this.callbackExecutor = callbackExecutor;
    }

    @Override public void cancel() {
      call.cancel();
    }

    @Override public void enqueue(final MyCallback<T> callback) {
      call.enqueue(new Callback<T>() {
        @Override public void onResponse(Call<T> call, Response<T> response) {
          // TODO if 'callbackExecutor' is not null, the 'callback' methods should be executed
          // on that executor by submitting a Runnable. This is left as an exercise for the reader.

          int code = response.code();
          if (code >= 200 && code < 300) {
            callback.success(response);
          } else if (code == 401) {
            callback.unauthenticated(response);
          } else if (code >= 400 && code < 500) {
            callback.clientError(response);
          } else if (code >= 500 && code < 600) {
            callback.serverError(response);
          } else {
            callback.unexpectedError(new RuntimeException("Unexpected response " + response));
          }
        }

        @Override public void onFailure(Call<T> call, Throwable t) {
          // TODO if 'callbackExecutor' is not null, the 'callback' methods should be executed
          // on that executor by submitting a Runnable. This is left as an exercise for the reader.

          if (t instanceof IOException) {
            callback.networkError((IOException) t);
          } else {
            callback.unexpectedError(t);
          }
        }
      });
    }

    @Override public MyCall<T> clone() {
      return new MyCallAdapter<>(call.clone(), callbackExecutor);
    }
  }
}

Here's how you may use it:

Retrofit retrofit = new Retrofit.Builder()
    .baseUrl("http://httpbin.org")
    .addCallAdapterFactory(new ErrorHandlingCallAdapterFactory())
    .addConverterFactory(GsonConverterFactory.create())
    .build();

HttpBinService service = retrofit.create(HttpBinService.class);
MyCall<Ip> ip = service.getIp();

ip.enqueue(new MyCallback<Ip>() {

    @Override public void success(Response<Ip> response) {
    System.out.println("SUCCESS! " + response.body().origin);
    }

    @Override public void unauthenticated(Response<?> response) {
    System.out.println("UNAUTHENTICATED");
    }

    @Override public void clientError(Response<?> response) {
    System.out.println("CLIENT ERROR " + response.code() + " " + response.message());
    }

    @Override public void serverError(Response<?> response) {
    System.out.println("SERVER ERROR " + response.code() + " " + response.message());
    }

    @Override public void networkError(IOException e) {
    System.err.println("NETWORK ERROR " + e.getMessage());
    }

    @Override public void unexpectedError(Throwable t) {
    System.err.println("FATAL ERROR " + t.getMessage());
    }
});

Answer 4

For handing cases specific to 401 centrally and also for retrying requests with new auth token, please refer to this stack overflow answer.