Асинхронные Http запросы

import org.json.JSONObject;
 
import javax.xml.bind.DatatypeConverter;
import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.*;
 
 
public abstract class abstractRESTAPITest {
    protected String apiUrl;
 
 
    public abstractRESTAPITest() {
    }
 
    protected byte[] sendRequest(JSONObject jsonObject) throws IOException {
        return this.sendRequest(jsonObject, (String) null, (String) null);
    }
    protected byte[] sendRequest(JSONObject jsonObject, String username, String password) throws IOException {
        HttpURLConnection httpURLConnection = (HttpURLConnection) (new URL(this.apiUrl)).openConnection();
        if (username != null && password != null) {
            String userPassword = username + ":" + password;
            httpURLConnection.setRequestProperty("Authorization", "Basic " + DatatypeConverter.printBase64Binary(userPassword.getBytes()));
        }
 
        httpURLConnection.setRequestProperty("Content-Type", "application/json");
        httpURLConnection.setDoOutput(true);
        DataOutputStream dataOutputStream = new DataOutputStream(httpURLConnection.getOutputStream());
        dataOutputStream.write(jsonObject.toString().getBytes());
        dataOutputStream.flush();
        System.out.println("REST send: " + jsonObject.toString());
        if (httpURLConnection.getResponseCode() != 200) {
            System.out.println("REST send error, http code " + httpURLConnection.getResponseCode() + " " + httpURLConnection.getResponseMessage());
            throw new IOException();
        } else {
            byte[] responseBody = null;
            StringBuilder data = new StringBuilder();
            BufferedReader br = new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream()));
            String line = "";
 
            while ((line = br.readLine()) != null) {
                data.append(line);
                responseBody = data.toString().getBytes();
            }
 
            if (br != null) {
                br.close();
            }
            return responseBody;
        }
    }
 
    public abstract boolean test();
 
}