I'm have some project, realtime sending RSSI and MAC of Bluetooth Low Energy. I've seen questions regarding MQTT reconnecting. But I'm confused when it is applied to my origin code.

MainActivity.Java

public class MainActivity extends AppCompatActivity {

    private Button turnon, changeLayout;
    MqttAndroidClient client;
    private boolean state=false;
    private BluetoothAdapter bluetoothAdapter;
    public static final int REQUEST_ACCESS_COARSE_LOCATION = 1;
    public static final int REQUEST_ENABLE_BLUETOOTH = 11;
    public static String mqtt_server,mqtt_port,mqtt_id,mqtt_topic;
    private TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getSupportActionBar().hide();
        setContentView(R.layout.activity_main);

        Log.d("Logger", "On Create Android");

        turnon = findViewById(R.id.turnon);
        changeLayout = findViewById(R.id.mqttSet);
        bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        textView = findViewById(R.id.textView4);

        textView.setText("id "+mqtt_id+" port "+mqtt_port+" server "+mqtt_server);
        client = new MqttAndroidClient(this.getApplicationContext(), "tcp://"+mqtt_server+":"+mqtt_port,mqtt_id);

        final Handler handler = new Handler();
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                stateCheck();
                Log.d("Logger", "State Check");
                handler.postDelayed(this, 1000);
            }
        }, 1000);

        turnon.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (!state){
                    turnon.setText("Turn Off");
                    Log.d("Logger", "Turn On State");
                    if(mqtt_server!=null||mqtt_id!=null||mqtt_port!=null||mqtt_topic!=null){
                    try {
                        Log.d("Logger", "Try ");
                        IMqttToken token = client.connect();
                        token.setActionCallback(new IMqttActionListener() {
                            @Override
                            public void onSuccess(IMqttToken asyncActionToken) {
                                Log.d("Logger", "Connect MQTT");
                                Toast.makeText(MainActivity.this,"connected!!",Toast.LENGTH_LONG).show();

                            }

                            @Override
                            public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
                                Log.d("Logger", "Connect Failed");
                                Toast.makeText(MainActivity.this,"connection failed!!",Toast.LENGTH_LONG).show();
                            }
                        });
                    } catch (MqttException e) {
                        e.printStackTrace();
                        Log.d("Logger", "error"+e);
                    }}
                    state = true;
                }else{
                    turnon.setText("Turn On");
                    state = false;
                }
            }
        });

        changeLayout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startActivity(new Intent(MainActivity.this,MqttActivity.class));
            }
        });
    }

    public void stateCheck(){
    if (state){
        Log.d("Logger", "Discover");   
    }
    }

}

The code I made has not been able to reconnect when my server restarts. Can anyone help me? But I'm asking for help with indicating which code I should change. Thanks