import okhttp3.RequestBody;
import okhttp3.Response;

public class PostExample {
  public static final MediaType JSON = MediaType.get("application/json; charset=utf-8");

  final OkHttpClient client = new OkHttpClient();

  String post(String url, String json) throws IOException {
    RequestBody body = RequestBody.create(json, JSON);
    Request request = new Request.Builder()
        .url(url)
        .post(body)
        .build();