Java , android app. Can not send post request HttpURLConnection conn

Question

i'm trying to send post request contain mac address of scanned devices by the following steps: 1/ scan devices 2/ send device mac addr to server 3/ return response with "1" and "-1"

-----if 1 -> device is correct

-----if -1 -> device is incorrect

By listing device is ok, but sending post request does not working, captured server, no request was made

private void scanLeDevice(final boolean enable) {
    final Button cancelButton = (Button) findViewById(R.id.btn_cancel);
    if (enable) {
        // Stops scanning after a pre-defined scan period.
        mHandler.postDelayed(new Runnable() {
            @Override
            public void run() {
                mScanning = false;
                uhf.stopScanBTDevices();
                cancelButton.setText(R.string.scan);
            }
        }, SCAN_PERIOD);

        mScanning = true;
        uhf.startScanBTDevices(new ScanBTCallback() {
            @Override
            public void getDevices(final BluetoothDevice bluetoothDevice, final int rssi, byte[] bytes) {
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        URL url = null;
                        HttpURLConnection conn = null;
                        String correct_device = "";
                        String device_mac     = bluetoothDevice.getAddress();
                        String device_name    = bluetoothDevice.getName();
                        // response correct_device = 1   == correct device, will available in list
                        // response correct_device = -1  == incorrect, does not need to appear in list
                        
                        try {
                            url = new URL("http://10.10.10.212/api/is_correct_device/");
                            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);

                            DataOutputStream os = new DataOutputStream(conn.getOutputStream());
                            os.writeBytes("{ \"check_update\" : " + device_mac + " }");

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

                            correct_device = conn.getResponseMessage();

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

                        if (correct_device.equals("1")) {
                            MyDevice myDevice = new MyDevice(device_mac, device_name);
                            addDevice(myDevice, rssi);
                        }
                        conn.disconnect();
                    }
                });
            }
        });
        cancelButton.setText(R.string.cancel);
    } else {
        mScanning = false;
        uhf.stopScanBTDevices();
        cancelButton.setText(R.string.scan);
    }
}

Thanks for save me!

Answer 1

You are calling url.openConnection() from runOnUiThread .

That is not possible!
All network communication code in Android must run in a background thread.

https://developer.android.com/training/basics/network-ops