public interface Api {
 @POST("product/getProductDetail")
 Observable<Goods_Bean> getGoods(@QueryMap Map<String,String> map);
 @POST("product/addCart")
 Observable<Add_Bean> getAdd(@QueryMap Map<String,String> map);
 @POST("product/getCarts")
 Observable<Query_bean> getShopCar(@QueryMap Map<String,String> map);
}

/**
 * 自定義攔截器.使用的是okhttp來定義的攔截器
 */
public class MyInterceptor implements Interceptor {
 @Override
 public Response intercept(Chain chain) throws IOException {
 Request request = chain.request();
 HttpUrl httpUrl = request
  .url()
  .newBuilder()
  .addQueryParameter("source", "android")
  .build();
 Request requestNew = request
  .newBuilder()
  .url(httpUrl)
  .build();
 return chain.proceed(requestNew);
 }
}

public class RetrofitUtil { 
 public static volatile Retrofit instance; 
 public static Retrofit getInstance(String baseUrl){ 
 if (instance==null){ 
  synchronized (RetrofitUtil.class){ 
  //攔截器 
  OkHttpClient client = new OkHttpClient.Builder() 
   .addInterceptor(new MyInterceptor()) 
   .build(); 
  //創(chuàng)建retrofit對象 
  instance = new Retrofit.Builder() 
   .baseUrl(baseUrl) 
   .client(client) 
   .addConverterFactory(GsonConverterFactory.create()) 
   .addCallAdapterFactory(RxJava2CallAdapterFactory.create()) 
   .build(); 
  } 
 } 
 return instance; 
 } 
}