Retrofitヘッダブロック

public class HttpUtils {
    public final Api api;
    private HttpUtils() {
        OkHttpClient client = new OkHttpClient.Builder().addNetworkInterceptor(new logging()).build();
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(Contast.url)
                .addConverterFactory(GsonConverterFactory.create())
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .client(client)
                .build();
        api = retrofit.create(Api.class);
    }

    // 
    class logging implements Interceptor {
        @Override
        public Response intercept(Chain chain) throws IOException {
            Request request = chain.request();
            Request.Builder builder = chain.request().newBuilder().addHeader("source", "android");
            Log.d("xxxxxx", "request:" + request);
            Response proceed = chain.proceed(request);
            return proceed;
        }
    }

    private static class GetDataNet{
        private static HttpUtils httpUtils=new HttpUtils();
    }
    public static HttpUtils getdatanet(){
        return GetDataNet.httpUtils;
    }
}