Realm background operation with Retrofit2 in AsyncTask

realm-background-operation-example-retrofit2.java

public class GetNewsPostAsyncTask
        extends AsyncTask<Void, Void, Void> {
    private Retrofit retrofit;
    private ApiService apiService;

    private long postId;

    public GetNewsPostAsyncTask(Retrofit retrofit, ApiService apiService, long postId) {
        this.retrofit = retrofit;
        this.apiService = apiService;
        this.postId = postId;
    }

    @Override
    protected Void doInBackground(Void... voids) {
        Realm realm = null;
        try {
            realm = Realm.getDefaultInstance();        // NOT RealmManager.getRealm()!
            Call<NewsPost> postCall = apiService.downloadPost(postId);
            Response<NewsPost> response = postCall.execute(); // sync download
            if(handleRetrofitError(retrofit, response)) {
                // error occurred, do something with error
                return null;
            }
            final NewsPost newsPost = response.body();
            realm.executeTransaction(new Realm.Transaction() {
                @Override
                public void execute(Realm realm) {
                    realm.insertOrUpdate(newsPost);
                    // assuming you can directly use RealmObject as JSON class
                    // typically I map between a dedicated JSON class and a RealmObject
                    // so that would mean `realm.insertOrUpdate(mapper.toRealm(newsPostJSON));`
                }
            });
        } finally {
            if(realm != null) {
                realm.close(); // ALWAYS CLOSE the background Realm
            }
        }
        return null; // NO NEED FOR `onPostExecute()`, the RealmChangeListener handles it automatically!
    }

    public boolean handleRetrofitError(Retrofit retrofit, Response<?> response) {
        // beautiful retrofit2 error handling
        if(response == null) {
            // do something with failure
            return true;
        }
        if(response != null && !response.isSuccessful() && response.errorBody() != null) {
            Converter<ResponseBody, ErrorResponse> converter = retrofit.responseBodyConverter(ErrorResponse.class,
                    new Annotation[0]); // <3 that empty array
            try {
                ErrorResponse errorResponse = converter.convert(response.errorBody());
                // do something with error
            } catch(IOException e) {
                // do something with failure
            }
            return true;
        }
        return false;
    }
}