Android activity to check for internet connection. This code not only checks if device is connected to a router or not but also determines whether internet is accessible. This is done by trying to reach a service within a specified time span.

NetworkStatusActivity.java

package com.example.arka.wifiinternet;

import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;

import java.io.IOException;
import java.lang.ref.WeakReference;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class NetworkStatusActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setImageResource(R.drawable.web_globe_solution);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                new NetworkStatus(view).execute();
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    private class NetworkStatus extends AsyncTask<String, String, String> {
        private WeakReference weakReference;

        boolean ableToConnect = false;
        boolean wifiConnected = false;
        boolean cellularDataActive = false;

        public NetworkStatus(View view) {
            weakReference = new WeakReference(view);
        }

        @Override
        protected String doInBackground(String... strings) {
            ConnectivityManager connectivityManager
                    = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();

            NetworkInfo wifi = connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
            NetworkInfo mobile = connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);

            if (wifi.isConnectedOrConnecting ()) {
                wifiConnected = true;
                cellularDataActive = false;
            } else if (mobile.isConnectedOrConnecting ()) {
                wifiConnected = false;
                cellularDataActive = true;
            } else {
                wifiConnected = false;
                cellularDataActive = false;
            }

            if (activeNetworkInfo != null && activeNetworkInfo.isConnectedOrConnecting()) {
                try {
                    URL url = new URL("http://google.com"); // keep your service here.. 
                    HttpURLConnection urlc = (HttpURLConnection) url.openConnection();
                    urlc.setConnectTimeout(2 * 1000); // set timeout here
                    urlc.connect();
                    if (urlc.getResponseCode() == 200) {
                        Log.d("Connection", "Success !");
                        ableToConnect = true;
                    } else {
                        ableToConnect = false;
                    }
                } catch (MalformedURLException e1) {
                    ableToConnect = false;
                } catch (IOException e) {
                    ableToConnect = false;
                }
            }
            return "";
        }

        @Override
        protected void onPostExecute(String values) {
            super.onPostExecute(values);

            if (weakReference == null) {
                return;
            }

            TextView textView = (TextView) findViewById(R.id.textView);
            View view = (View) weakReference.get();

            if (ableToConnect) {
                Snackbar.make(view, "Yo Internet :)", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
                textView.setText("Yo Internet :)");
            } else {
                Snackbar.make(view, "Not connected!! :(", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
                textView.setText("Not connected!! :(");
            }

            if (wifiConnected) {
                textView.setText("Connected to a Wifi");
            } else if (cellularDataActive) {
                textView.setText("Cellular Data");
            } else {
                textView.setText("Not Connected");
            }
        }
    }
}