@RestController
public class TesteController {
    @RequestMapping(value = "/teste123", method = RequestMethod.POST)
    public Programa test(@RequestBody Programa prog) {
        System.out.println(prog);
        return new Programa();
    }
}

$http.post("/teste123", {id: 'asd', txtPrograma: 'adsadasd'})
        .then(function (response) {
            console.log(response);
        }, function (response) {
            console.log(response);
        })

public interface ExecucaoService {

@POST("execucao/gravaLote")
public Call<Programa> gravaLote(@Body Programa programa);}

private static OkHttpClient.Builder httpClient = new OkHttpClient.Builder();
private static Retrofit.Builder builder =
        new Retrofit.Builder()
                .baseUrl(baseUrlWS)
                .addConverterFactory(GsonConverterFactory.create());
        String credentials = username + ":" + password;
        final String basic = "Basic " + Base64.encodeToString(credentials.getBytes(), Base64.NO_WRAP);

        httpClient.addInterceptor(new Interceptor() {
            @Override
            public okhttp3.Response intercept(Interceptor.Chain chain) throws IOException {
                Request original = chain.request();

                Request.Builder requestBuilder = original.newBuilder()
                        .header("Authorization", basic)
                        .header("Accept", "application/json")
                        .method(original.method(), original.body());
                Request request = requestBuilder.build();
                return chain.proceed(request);
            }
        });
      OkHttpClient client = httpClient.build();
    Retrofit retrofit = builder.client(client).build();
    // retrofit.create(serviceClass); aqui pego a instancia do serviço criada.