代码实现单例设计模式：Bill Pugh 在 Retrofit 对象上

Question

我一直在尝试使用私有静态类来实现 Bill Pugh 单例设计模式，以返回单例改造实例。到目前为止，我已经能够提出以下代码。有人可以帮我检查这段代码并确认这是否是 Bill Pugh 先生自己建议的单例设计模式的正确实现，或者建议我一种正确的实现方式。

public class SingletonRetrofit {

    private SingletonRetrofit(){}

    private static class SingletonRetrofitHelper {

        private static OkHttpClient okHttpClient;
        private static Retrofit retrofit;

        private static Retrofit makeRetrofit() {

            HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor();
            interceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
            okHttpClient = new OkHttpClient.Builder()
            .addInterceptor(interceptor)
            .readTimeout(20, TimeUnit.SECONDS)
            .connectTimeout(15, TimeUnit.SECONDS)
            .build();

            retrofit = new Retrofit.Builder()
            .baseUrl("http://ci.draftserver.com/hornsbyapp/webservice/")
            .client(okHttpClient)
            .addConverterFactory(ScalarsConverterFactory.create())
            .addConverterFactory(GsonConverterFactory.create())
            .build();

            return retrofit;

        }
    }

    public static Retrofit getInstance() {
        return SingletonRetrofitHelper.makeRetrofit();
    }
}

Answer 1

使用这个：

public class Apiclient {

    private static final String BASE_URL ="URL";
    private static Retrofit retrofit = null;

    public static Retrofit getClient() {

        if (retrofit == null) {

          OkHttpClient.Builder httpClient2 = new OkHttpClient.Builder();
          httpClient2.addNetworkInterceptor(new Interceptor() {

            @Override
            public Response intercept(Chain chain) throws IOException {
                Request.Builder builder = chain.request().newBuilder();
                builder.addHeader("site_id","1");
                return chain.proceed(builder.build());
            }
          });
          OkHttpClient client = httpClient2.build();

            retrofit = new Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .client(client)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
         }
         return retrofit;
    }
}