Clase para hacer peticion post y get desde java Android es necesario usar el patron de diseño observador

SendPostRequest.java

import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.util.Log;
import com.pcflex.android.patrones.ObjObervador;
import com.pcflex.android.patrones.ObjObservable;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.util.Iterator;
import javax.net.ssl.HttpsURLConnection;

/**
 * Created by Juan on 18/09/2017.
 */

public class SendPostRequest extends AsyncTask<String, Void, String> implements ObjObservable {

    private String  url;
    private JSONObject parametros;
    private String respuesta;
    private ObjObervador obervador;
    private ProgressDialog pDialog;

    public SendPostRequest(String url, JSONObject parametros, ProgressDialog dialog){
        this.url = url;
        this.parametros = parametros;
        this.pDialog = dialog;

    }

    public void setObervador(ObjObervador obervador) {
        this.obervador = obervador;
    }



    protected void onPreExecute(){
        if(this.pDialog !=null) {
            pDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
            pDialog.setCancelable(false);
            pDialog.show();
        }
    }

    protected String doInBackground(String... arg0) {

        try {
            URL url = new URL(this.url); // here is your URL path
            Log.e("Respuesta URL",this.url);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(15000 /* milliseconds */);
            conn.setConnectTimeout(15000 /* milliseconds */);
            conn.setRequestMethod("POST");
            conn.setDoInput(true);
            conn.setDoOutput(true);

            OutputStream os = conn.getOutputStream();
            BufferedWriter writer = new BufferedWriter(
                    new OutputStreamWriter(os, "UTF-8"));
            writer.write(getPostDataString());

            writer.flush();
            writer.close();
            os.close();

            int responseCode=conn.getResponseCode();

            if (responseCode == HttpsURLConnection.HTTP_OK) {

                Log.e("resultado","Ok");

                BufferedReader in=new BufferedReader(
                        new InputStreamReader(
                                conn.getInputStream()));
                StringBuffer sb = new StringBuffer("");
                String line="";

                while((line = in.readLine()) != null) {

                    sb.append(line);
                    break;
                }

                in.close();

                return sb.toString();

            }
            else {
                Log.e("resultado","no 200");
                return new String("201");
            }
        }
        catch(Exception e){
            Log.e("resultado","Fallo en la conexion");
            return new String("500");
        }

    }

    @Override
    protected void onPostExecute(String result) {
        pDialog.dismiss();
        this.respuesta = result;
        this.notificar();
    }


    public String getPostDataString() throws Exception {

        StringBuilder result = new StringBuilder();
        boolean first = true;

        Iterator<String> itr = this.parametros.keys();

        while(itr.hasNext()){

            String key= itr.next();
            Object value = this.parametros.get(key);

            if (first)
                first = false;
            else
                result.append("&");

            result.append(URLEncoder.encode(key, "UTF-8"));
            result.append("=");
            result.append(URLEncoder.encode(value.toString(), "UTF-8"));

        }
        return result.toString();
    }

    @Override
    public void notificar() {
        this.obervador.update(this.respuesta);
    }
}

Uso

ProgressDialog pDialog = new ProgressDialog(this);
        pDialog.setMessage("Cargando...");
        JSONObject postDataParams = new JSONObject();
        try {
            //Se agregan parametros
            postDataParams.put("device_token",gcm_token);
        } catch (JSONException e) {
            e.printStackTrace();
        }
        SendPostRequest send = new SendPostRequest(Config.SERVER_URL+"/check",postDataParams,pDialog);
        send.setObervador(new ObjObervador() {
            @Override
            public void update(String respuesta) {
                Log.d(TAG,"respuesta"+respuesta);         
                }
            }
        });
        send.execute();