how to draw the polyline of the route travelled by the assets in android?

Question

Hello I am currently working on assets tracking project in android application.

Here is what i have:

I have already implemented the assets tracking application where they broadcast their locations for every 3 sec and i used google firebase's real time database to store those data.

I have a tracking display app that will display the assets current location.
It only show the assets current location.

But i need to draw the polyline from where the assets started the service using tracking application till the current location of the assets.

I have very basic idea about google map api.

Thanks in advance. bellow is code to display the assets location.

public class DisplayActivity extends FragmentActivity implements OnMapReadyCallback {

    private static final String TAG = DisplayActivity.class.getSimpleName();
    private HashMap<String, Marker> mMarkers = new HashMap<>();
    private GoogleMap mMap;
    private AutoCompleteTextView autoCompleteTextView;

    private ArrayList<LatLng> points; //added
    Polyline line; //added

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

        autoCompleteTextView=(AutoCompleteTextView)findViewById(R.id.autoCompleteTextView);
        autoCompleteTextView.setSingleLine(true);
        autoCompleteTextView.setImeOptions(EditorInfo.IME_ACTION_SEARCH);


        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);

        points = new ArrayList<LatLng>(); //added

    }

    @Override
    public void onMapReady(GoogleMap googleMap) {
        // Authenticate with Firebase when the Google map is loaded
        mMap = googleMap;
        mMap.setMaxZoomPreference(16);
        loginToFirebase();
    }

    private void loginToFirebase() {
        String email = getString(R.string.firebase_email);
        String password = getString(R.string.firebase_password);
        // Authenticate with Firebase and subscribe to updates
        FirebaseAuth.getInstance().signInWithEmailAndPassword(
                email, password).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(Task<AuthResult> task) {
                if (task.isSuccessful()) {
                    subscribeToUpdates();
                    Log.d(TAG, "firebase auth success");
                } else {
                    Log.d(TAG, "firebase auth failed");
                }
            }
        });
    }

    private void subscribeToUpdates() {
        DatabaseReference ref = FirebaseDatabase.getInstance().getReference(getString(R.string.firebase_path));
        ref.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String previousChildName) {
                setMarker(dataSnapshot);
            }

            @Override
            public void onChildChanged(DataSnapshot dataSnapshot, String previousChildName) {
                setMarker(dataSnapshot);
            }

            @Override
            public void onChildMoved(DataSnapshot dataSnapshot, String previousChildName) {
                setMarker(dataSnapshot);
            }

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {

            }

            @Override
            public void onCancelled(DatabaseError error) {
                Log.d(TAG, "Failed to read value.", error.toException());
            }
        });
    }

    private void setMarker(DataSnapshot dataSnapshot) {
        String key = dataSnapshot.getKey();
        HashMap<String, Object> value = (HashMap<String, Object>) dataSnapshot.getValue();
        double lat = Double.parseDouble(value.get("latitude").toString());
        double lng = Double.parseDouble(value.get("longitude").toString());
        LatLng location = new LatLng(lat, lng);
        if (!mMarkers.containsKey(key)) {
            mMarkers.put(key, mMap.addMarker(new MarkerOptions().title(key).position(location)));
        } else {
            mMarkers.get(key).setPosition(location);

        }
        LatLngBounds.Builder builder = new LatLngBounds.Builder();
        for (Marker marker : mMarkers.values()) {
            builder.include(marker.getPosition());
        }
        mMap.animateCamera(CameraUpdateFactory.newLatLngBounds(builder.build(), 300));
    }
}