1   Retrofit retrofit = new Retrofit.Builder()
                            .addConverterFactory(ScalarsConverterFactory.create())  //请求返回字符串，如需返回对象，需使用converter-gson
                            .baseUrl("http://www.baidu.com").build();

   DataService service = retrofit.create(DataService.class);  

 public interface DataService {

     @GET("/")

     Call<String> getData();

 }

 Call<String> data = service.getData();

  //String msg=data.execute().body().toString();//同步执行

　　//异步执行

　  data.enqueue(new Callback<String>() {

          @Override

          public void onResponse(Call<String> call, Response<String> response) {

          }

          @Override

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

          }

          });