Show Current Location In A Google Map For Android

Here is a full Activity class that places a Marker at the current location, and also moves the camera to the current position.
There are a few things going on in sequence here:

Check Location permission
Once Location permission is granted, call setMyLocationEnabled(), build the GoogleApiClient, and connect it
Once the GoogleApiClient is connected, request location updates

MapLocationActivity.java

public class MapLocationActivity extends AppCompatActivity implements OnMapReadyCallback,
        GoogleApiClient.ConnectionCallbacks,
        GoogleApiClient.OnConnectionFailedListener,
        LocationListener {
          
    GoogleMap mGoogleMap;
    SupportMapFragment mapFrag;
    LocationRequest mLocationRequest;
    GoogleApiClient mGoogleApiClient;
    Location mLastLocation;
    Marker mCurrLocationMarker;
          
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState); setContentView(R.layout.activity_main);
        getSupportActionBar().setTitle("Map Location Activity");
        mapFrag = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
        mapFrag.getMapAsync(this);
    }
          
    @Override
    public void onPause() {
        super.onPause();
        //stop location updates when Activity is no longer active
        if (mGoogleApiClient != null) {
          LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, this);
        }
    }
          
    @Override
    public void onMapReady(GoogleMap googleMap) {
        mGoogleMap=googleMap;
        mGoogleMap.setMapType(GoogleMap.MAP_TYPE_HYBRID);
        //Initialize Google Play Services
        if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) { 
          if (ContextCompat.checkSelfPermission(this,
                    Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED) { 
            //Location Permission already granted 
            buildGoogleApiClient(); 
            mGoogleMap.setMyLocationEnabled(true);
          } else {
            //Request Location Permission
            checkLocationPermission();
          }
    } else {
        buildGoogleApiClient();
        mGoogleMap.setMyLocationEnabled(true); }
  }
          
  protected synchronized void buildGoogleApiClient() { 
      mGoogleApiClient = new GoogleApiClient.Builder(this).addConnectionCallbacks(this).addOnConnectionFailedListener(this).addApi(LocationServices.API).build();
        mGoogleApiClient.connect();
  }
          
  @Override
  public void onConnected(Bundle bundle) {
      mLocationRequest = new LocationRequest();
      mLocationRequest.setInterval(1000);
      mLocationRequest.setFastestInterval(1000);
      mLocationRequest.setPriority(LocationRequest.PRIORITY_BALANCED_POWER_ACCURACY);
      if (ContextCompat.checkSelfPermission(this,
                Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED) {
            LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this); 
      }
  }
          
  @Override
  public void onConnectionSuspended(int i) {}
          
  @Override
  public void onConnectionFailed(ConnectionResult connectionResult) {}
          
  @Override
  public void onLocationChanged(Location location) {
      mLastLocation = location;
      if (mCurrLocationMarker != null) {
          mCurrLocationMarker.remove();
      }
      //Place current location marker
      LatLng latLng = new LatLng(location.getLatitude(), location.getLongitude()); 
      MarkerOptions markerOptions = new MarkerOptions(); markerOptions.position(latLng);
      markerOptions.title("Current Position");
      markerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_MAGENTA));         mCurrLocationMarker = mGoogleMap.addMarker(markerOptions);
      //move map camera
      mGoogleMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
      mGoogleMap.animateCamera(CameraUpdateFactory.zoomTo(11));
    
    //stop location updates
    if (mGoogleApiClient != null) {
      LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, this); 
    }
  }
  
  public static final int MY_PERMISSIONS_REQUEST_LOCATION = 99; 

  private void checkLocationPermission() {
    if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
      // Should we show an explanation?
      if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.ACCESS_FINE_LOCATION)) {
      // Show an explanation to the user *asynchronously* -- don't block 
      // this thread waiting for the user's response! After the user
      // sees the explanation, try again to request the permission.
      new AlertDialog.Builder(this).setTitle("Location Permission Needed").setMessage("This app needs the Location permission, please accept to use location functionality").setPositiveButton("OK", new DialogInterface.OnClickListener() { 
        @Override
        public void onClick(DialogInterface dialogInterface, int i) { 
          //Prompt the user once explanation has been shown
          ActivityCompat.requestPermissions(MapLocationActivity.this, 
                new String[]{
                  Manifest.permission.ACCESS_FINE_LOCATION 
                }, MY_PERMISSIONS_REQUEST_LOCATION );
        } 
      }).create().show();
        
  } else {
  // No explanation needed, we can request the permission.
      ActivityCompat.requestPermissions(this,
            new String[]{
              Manifest.permission.ACCESS_FINE_LOCATION
            }, MY_PERMISSIONS_REQUEST_LOCATION );
      } 
    }
  }
          
  @Override
  public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
    switch (requestCode) {
      case MY_PERMISSIONS_REQUEST_LOCATION: {
        // If request is cancelled, the result arrays are empty.
        if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
              // permission was granted, yay! Do the
              // location-related task you need to do.
              if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)
                          == PackageManager.PERMISSION_GRANTED) {
                  if (mGoogleApiClient == null) { 
                    buildGoogleApiClient();
              }
              mGoogleMap.setMyLocationEnabled(true); 
          }
        } else {
            // permission denied, boo! Disable the
            // functionality that depends on this permission. 
            Toast.makeText(this, "permission denied", Toast.LENGTH_LONG).show();
        }
            return; 
      }
        // other 'case' lines to check for other
        // permissions this app might request
    } 
  }
}

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent">
        <fragment xmlns:android="http://schemas.android.com/apk/res/android"
              xmlns:tools="http://schemas.android.com/tools"
              xmlns:map="http://schemas.android.com/apk/res-auto"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:id="@+id/map"
              tools:context="com.example.app.MapLocationActivity"
              android:name="com.google.android.gms.maps.SupportMapFragment"/>
</LinearLayout>

Result:

Show explanation if needed on Marshmallow and Nougat using an AlertDialog (this case happens when the user had previously denied a permission request, or had granted the permission and then later revoked it in the settings):