Download file with Retrofit 2, OkHttp, Okio and RxJava

DownloadFileWithRetrofit2RxJava.java

import com.squareup.okhttp.ResponseBody;
import okio.BufferedSink;
import okio.Okio;
import retrofit.Response;
import retrofit.http.GET;
import retrofit.http.Query;
import rx.Observable;

interface ApiService {

    @GET("/media/download")
    Observable<Response<ResponseBody>> download(@Query("id") String id);

}

public Observable<File> download(String id) {
    return service.download(id)
            .flatMap(this::saveFile);
}

public Observable<File> saveFile(Response<ResponseBody> response) {
    return Observable.create((Observable.OnSubscribe<File>) subscriber -> {
        try {
            // you can access headers of response
            String header = response.headers().get("Content-Disposition");
            // this is specific case, it's up to you how you want to save your file
            // if you are not downloading file from direct link, you might be lucky to obtain file name from header
            String fileName = header.replace("attachment; filename=", "");
            // will create file in global Music directory, can be any other directory, just don't forget to handle permissions
            File file = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MUSIC).getAbsoluteFile(), fileName);
            
            BufferedSink sink = Okio.buffer(Okio.sink(file));
            // you can access body of response
            sink.writeAll(response.body().source());
            sink.close();
            subscriber.onNext(file);
            subscriber.onCompleted();
        } catch (IOException e) {
            e.printStackTrace();
            subscriber.onError(e);
        }
    });
}

Up for listen download progress and download notification @lsurvila