Retrofit

Util 

public class HttpUtil {

    public final Api api;

    public HttpUtil() {
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(Contest.UTL)
                .addConverterFactory(GsonConverterFactory.create())
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .build();

        api = retrofit.create(Api.class);

    }
    private static class GetDataNet{

        public static HttpUtil httpUtils = new HttpUtil();

    }
    public static HttpUtil getInstence(){
        return GetDataNet.httpUtils;
    }

}

model

public  static  Observable<HomeCommodityBean> getData(String page){
        Observable<HomeCommodityBean> commodity = HttpUtil.getInstence().api.getCommodity(page);
        return commodity;
    }

拦截器

 private HttpUtils(){
        OkHttpClient client = new OkHttpClient.Builder().addNetworkInterceptor(new Logging()).build();

        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(Contest.url)
                .addConverterFactory(GsonConverterFactory.create())
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .client(client)
                .build();

        api = retrofit.create(Api.class);
    }
            
    private class Logging implements Interceptor {
        @Override
        public Response intercept(Chain chain) throws IOException {
            Request request = chain.request();
            Request.Builder builder = request.newBuilder().addHeader("soucre", "android");
            Response proceed = chain.proceed(request);
            return proceed;
        }
    }