1.第一步將Retrofit和Rxjava關聯起來
public Retrofit getRetrofit(String baseUrl){
    Retrofit retrofit=new Retrofit.Builder()
            .client(setOkHttpClick())
            .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
            .addConverterFactory(GsonConverterFactory.create())
            .baseUrl(baseUrl)
            .build();
    return retrofit;

2.把Retrofit的返回值替換為Retrofit的Observer物件

public interface BeautyServer {
    @POST
    Observable<TodayNewsRes> getBeauty(@Url String url);
}
3.呼叫介面返回資料
RetrofitClient.getInstance().getRetrofit(BASE_URL).create(BeautyServer.class).getBeauty("api/today")
        .subscribeOn(Schedulers.newThread())
        .observeOn(Schedulers.io())//工作執行緒
        .doOnNext(new Action1<TodayNewsRes>() {
            @Override
            public void call(TodayNewsRes todayNewsRes) {
                Logger.d(todayNewsRes);
            }
        })
        .observeOn(AndroidSchedulers.mainThread())//切換為主執行緒返回資料
        .subscribe(new Subscriber<TodayNewsRes>() {
            @Override
            public void onCompleted() {

            }

            @Override
            public void onError(Throwable e) {

            }

            @Override
            public void onNext(TodayNewsRes todayNewsRes) {
                toastMsg(todayNewsRes.toString());
                //Logger.d(todayNewsRes.toString());
            }
        });