//on create

   Button button = (Button) findViewById(R.id.button);

        login = findViewById((R.id.Login));
        password = findViewById(R.id.Password);
        button.setOnClickListener( new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                sendPost();
                try {
                    TimeUnit.SECONDS.sleep(2);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                sendPost();
            }
        });



public void sendPost() {
        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    URL url = new URL("http://cargoalgps.cba.pl/api/uzytkownik/login.php");
                    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                    conn.setRequestMethod("POST");
                    conn.setRequestProperty("Content-Type", "application/json;charset=UTF-8");
                    conn.setRequestProperty("Accept","application/json");
                    conn.setDoOutput(true);
                    conn.setDoInput(true);

                    JSONObject jsonParam = new JSONObject();
                    jsonParam.put("login", login.getText());
                    jsonParam.put("haslo", password.getText());

                    Log.i("JSON", jsonParam.toString());
                    DataOutputStream os = new DataOutputStream(conn.getOutputStream());
                    //os.writeBytes(URLEncoder.encode(jsonParam.toString(), "UTF-8"));
                    os.writeBytes(jsonParam.toString());

                    os.flush();
                    os.close();
                    if(conn.getResponseCode() == 200){
                        text.setText("zalogowano");
                    }
                   else{
                        text.setText("bledne dane");
                    }


                    conn.disconnect();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });

        thread.start();
    }