retrofit-custom-error-handling.java

// on error the server sends JSON
/*
 { "error": { "data": { "message":"A thing went wrong" } } } 
*/

// create model classes..

public class ErrorResponse {
  Error error;
  
  public static class Error {
    Data data;
  
    public static class Data {
       String message;
    }  
  }
}

// 

/**
 * Converts the complex error structure into a single string you can get with error.getLocalizedMessage() in Retrofit error handlers.
 * Also deals with there being no network available
 * 
 * Uses a few string IDs for user-visible error messages
 */
private static class CustomErrorHandler implements ErrorHandler {
    private final Context ctx;

    public CustomErrorHandler(Context ctx) {
        this.ctx = ctx;
    }

    @Override
    public Throwable handleError(RetrofitError cause) {
        String errorDescription;

        if (cause.isNetworkError()) {
            errorDescription = ctx.getString(R.string.error_network);
        } else {
            if (cause.getResponse() == null) {
                errorDescription = ctx.getString(R.string.error_no_response);
            } else {

                // Error message handling - return a simple error to Retrofit handlers..
                try {
                    ErrorResponse errorResponse = (ErrorResponse) cause.getBodyAs(ErrorResponse.class);
                    errorDescription = errorResponse.error.data.message;
                } catch (Exception ex) {
                    try {
                        errorDescription = ctx.getString(R.string.error_network_http_error, cause.getResponse().getStatus());
                    } catch (Exception ex2) {
                        Log.e(TAG, "handleError: " + ex2.getLocalizedMessage());
                        errorDescription = ctx.getString(R.string.error_unknown);
                    }
                }
            }
        }

        return new Exception(errorDescription);
    }
}

// When creating the Server...

retrofit.RestAdapter restAdapter = new retrofit.RestAdapter.Builder()
  .setEndpoint(apiUrl)
  .setLogLevel(retrofit.RestAdapter.LogLevel.FULL)
  .setErrorHandler(new CustomErrorHandler(ctx))  // use error handler..
  .build();
                        
server = restAdapter.create(Server.class);

// Now when calling server methods, get simple error out like this:

server.postSignIn(login, new Callback<HomePageResponse>() {
                @Override
                public void success(HomePageResponse homePageResponse, Response response) {
                  // Do success things!
                }

                @Override
                public void failure(RetrofitError error) {
                    error.getLocalizedMessage(); // <-- this is the message to show to user.
                }
            });