Complete MainActivity.java code with solution for http and location

Step 1)

add dependency:

implementation 'com.loopj.android:android-async-http:1.4.9' 

read documentation at
http://loopj.com/android-async-http/

Step 2) Add Code for Activity: 

public class MainActivity extends AppCompatActivity {
    AsyncHttpClient client;
    TextView tv;
    SeekBar sb;
    ProgressBar pb;
    String url = "http://172.168.22.15/control?lightno=1&state=";

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

        Button btnHttp = findViewById(R.id.btnHttp);
        client = new AsyncHttpClient();
        tv = findViewById(R.id.txtv);
        sb = findViewById(R.id.seekBar);
        pb = findViewById(R.id.progressBar2);

        pb.setVisibility(View.GONE);

        sb.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            int val = 0;

            @Override
            public void onProgressChanged(SeekBar seekBar, int i, boolean b) {
                val = i;
            }

            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {
            }

            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {
                pb.setVisibility(View.VISIBLE);
                RequestParams params = new RequestParams();

                params.put("lightno", "1");//URL parameter in Object form
                params.put("state", val);

                //http://172.168.22.15/control?lightno=1&state=85
                client.get(url, params, new TextHttpResponseHandler() {
                    @Override
                    public void onFailure(int statusCode, Header[] headers, String responseString, Throwable throwable) {
                        pb.setVisibility(View.GONE);
                    }

                    @Override
                    public void onSuccess(int statusCode, Header[] headers, String responseString) {
                        //Toast.makeText(MainActivity.this,"",Toast.LENGTH_LONG);
                        Log.d("http", "happening" + responseString);
                        tv.setText(responseString);
                        pb.setVisibility(View.GONE);

                    }
                });
            }
        });

        Button bt = findViewById(R.id.btnLocation);//Button for getting Location Data from GPS sensor

        bt.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
                LocationListener ll = new LocationListener() {
                    @Override
                    public void onLocationChanged(Location location) {
                        double lt = location.getLatitude();
                        double ln = location.getLongitude();
                        tv.setText(lt+","+ln);
                    }

                    @Override
                    public void onStatusChanged(String s, int i, Bundle bundle) {

                    }

                    @Override
                    public void onProviderEnabled(String s) {

                    }

                    @Override
                    public void onProviderDisabled(String s) {

                    }
                };
                if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {

                    lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, ll);
                    return;
                }
                String lp = LocationManager.GPS_PROVIDER;
                Location lastLocation = lm.getLastKnownLocation(lp);
                double ltt=lastLocation.getLatitude();
                double lon=lastLocation.getLongitude();
                tv.setText(ltt+","+lon);
                Log.d("Location############ ",""+ltt);

            }
        });

        btnHttp.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                pb.setVisibility(View.VISIBLE);
                RequestParams params = new RequestParams();
                params.put("lightno","1");
                params.put("state","56");
                //http://172.168.22.15/control?lightno=1&state=1
                client.get("http://www.iocare.in/testurl", params, new TextHttpResponseHandler() {
                    @Override
                    public void onFailure(int statusCode, Header[] headers, String responseString, Throwable throwable) {
                        pb.setVisibility(View.GONE);
                    }

                    @Override
                    public void onSuccess(int statusCode, Header[] headers, String responseString) {
                        //Toast.makeText(MainActivity.this,"",Toast.LENGTH_LONG);
                        Log.d("http","happening"+responseString);
                        tv.setText(responseString);
                        pb.setVisibility(View.GONE);

                    }
                });
            }
        });
    }
}

Step 3 ) Update your UI as per requirement of Code

UI needs 6 controls

1) Button to test AsyncHttp library http request to NodeMCU

2) Second Button to test Location service and get latitude and Longitude

4) SeekBar control to send dimming data to NodeMCU with AsyncHttp library

5) A progressbar Control to show progress of request.

6) A textView to hold some result data.