public class RetrofitFactory {

    private final Gson mGson;

    public RetrofitFactory() {
        mGson = new GsonBuilder()
                .setDateFormat("yyyy-MM-dd hh:mm:ss")
                .create();
    }

    private static class SingleOnHolder {
        private static final RetrofitFactory INSTANCE = new RetrofitFactory();
    }

    public static RetrofitFactory getInstance() {
        return SingleOnHolder.INSTANCE;
    }

    public <S> S createService(Class<S> serviceClass) {
        String baseUrl = "";
        try {
            Field field = serviceClass.getField("BASE_URL");
            try {
                baseUrl = (String) field.get(field);
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        }

        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(baseUrl)
                .client(getOkHttp())
                .addConverterFactory(GsonConverterFactory.create(mGson))
                .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
                .build();
        return retrofit.create(serviceClass);
    }

    private final static long DEFAULT_TIMEOUT = 10;

    private OkHttpClient getOkHttp() {
        HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor(new HttpLoggingInterceptor.Logger() {
            @Override
            public void log(String message) {
                Log.i("OkHttp", message);
            }
        });
        interceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
        OkHttpClient.Builder okhttp = new OkHttpClient.Builder();
        okhttp.addInterceptor(interceptor);
        okhttp.addNetworkInterceptor(new CacheInterceptor());
        okhttp.connectTimeout(DEFAULT_TIMEOUT, TimeUnit.SECONDS);
        okhttp.writeTimeout(DEFAULT_TIMEOUT, TimeUnit.SECONDS);
        okhttp.readTimeout(DEFAULT_TIMEOUT, TimeUnit.SECONDS);
        okhttp.cache(new Cache(new File(Constant.CACHE), 10 * 1024 * 1024));
        return okhttp.build();
    }
}


public interface GankService {

    String BASE_URL = "http://gank.io/";

    @GET("api/data/{type}/{size}/{page}")
    Observable<GankDataBean> getGankData(@Path("type") String type, @Path("size") int size, @Path("page") int page);
}

RetrofitFactory.getInstance().createService(GankService.class).getGankData(xxxx);