public interface ICollection {

    @GET("/collection/{cid}")

    Call<ResponseBody> getCollection(@Path("cid") String cid);

}

Retrofit retrofit = new Retrofit.Builder()

                .baseUrl(baseUrl)

                .client(new OkHttpClient())//不加转换器

                .build();

        ICollection iCollection = retrofit.create(ICollection.class);

        Call<ResponseBody> call = iCollection.getCollection(ID);

        call.enqueue(new Callback<ResponseBody>() {

            @Override

            public void onResponse(Call<ResponseBody> call, retrofit2.Response<ResponseBody> response) {

                try {

                    Message msg = Message.obtain();

                    msg.what = 1;

                    msg.obj = response.body().string();

                    handler.sendMessage(msg);

                }

                catch (IOException e){e.printStackTrace();}

            }

            @Override

            public void onFailure(Call<ResponseBody> call, Throwable t) {

            }

        });