public class MyNotificationManager {

public static final int ID_BIG_NOTIFICATION = 234;
public static final int ID_SMALL_NOTIFICATION = 235;

private Context mCtx;

public MyNotificationManager(Context mCtx) {
    this.mCtx = mCtx;
}

//the method will show a big notification with an image
//parameters are title for message title, message for message text, url of the big image and an intent that will open
//when you will tap on the notification
public void showBigNotification(String title, String message, Bitmap image, Intent intent) {
    int requestID = (int) System.currentTimeMillis();
    PendingIntent resultPendingIntent =
            PendingIntent.getActivity(
                    mCtx,
                    requestID,
                    intent,
                    0
            );
   Notification.BigPictureStyle bigPictureStyle = new Notification.BigPictureStyle();
    bigPictureStyle.bigPicture(image);
    bigPictureStyle.setSummaryText(message);
    Notification.Builder mBuilder = new Notification.Builder(mCtx);
    Notification notification;
    notification = mBuilder.setSmallIcon(R.drawable.notification_icon).setTicker(title).setWhen(0)
            .setAutoCancel(true)
            .setContentTitle(title)
            .setStyle(bigPictureStyle)
            .setSmallIcon(R.drawable.notification_icon)
            .setLargeIcon(BitmapFactory.decodeResource(mCtx.getResources(),R.drawable.mr_hot_circle))
            .addAction(R.drawable.logout_icon,"Open App",resultPendingIntent)
            //.setContentIntent(resultPendingIntent)
            .build();


    notification.flags |= Notification.FLAG_AUTO_CANCEL;

    NotificationManager notificationManager = (NotificationManager) mCtx.getSystemService(Context.NOTIFICATION_SERVICE);
    notificationManager.notify(requestID, notification);
}

//the method will show a small notification
//parameters are title for message title, message for message text and an intent that will open
//when you will tap on the notification
public void showSmallNotification(String title, String message, Intent intent) {
    int requestID = (int) System.currentTimeMillis();
    PendingIntent resultPendingIntent =
            PendingIntent.getActivity(
                    mCtx,
                    requestID,
                    intent,
                    0
            );


    Notification.Builder mBuilder = new Notification.Builder(mCtx);
    Notification notification;
    notification = mBuilder.setSmallIcon(R.drawable.notification_icon).setTicker(title).setWhen(0)
            .setAutoCancel(true)
            .setContentIntent(resultPendingIntent)
            .setContentTitle(title)
            .setSmallIcon(R.drawable.notification_icon)
            .setLargeIcon(BitmapFactory.decodeResource(mCtx.getResources(),R.drawable.mr_hot_circle))
            .setContentText(message)
            .build();

    notification.flags |= Notification.FLAG_AUTO_CANCEL;

    NotificationManager notificationManager = (NotificationManager) mCtx.getSystemService(Context.NOTIFICATION_SERVICE);
    notificationManager.notify(requestID, notification);
}

//The method will return Bitmap from an image URL

public class MyFirebaseMessagingService extends FirebaseMessagingService {
private static final String TAG = "MyFirebaseMsgService";
MyNotificationManager mNotificationManager;
String title,message,imageUrl;
Intent intent;
@Override
public void onMessageReceived(RemoteMessage remoteMessage) {
    if (remoteMessage.getData().size() > 0) {
        Log.e(TAG, "Data Payload: " + remoteMessage.getData().toString());
        try {

            if (remoteMessage.getNotification() != null) {
                Log.d(TAG, "Message Notification Body: " + remoteMessage.getNotification().getBody());
            }
            title = remoteMessage.getData().get("title");
            message = remoteMessage.getData().get("message");
            imageUrl = remoteMessage.getData().get("image");

            //creating MyNotificationManager object
            mNotificationManager = new MyNotificationManager(getApplicationContext());

            //creating an intent for the notification
            intent = new Intent(getApplicationContext(), HomeActivity.class);
            intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP|Intent.FLAG_ACTIVITY_SINGLE_TOP);
            /*TaskStackBuilder stackBuilder = TaskStackBuilder.create(this);
            stackBuilder.addParentStack(Welcome.class);
            stackBuilder.addNextIntent(intent);*/

            //if there is no image
            if(imageUrl.equals("")){
                //displaying small notification
                mNotificationManager.showSmallNotification(title, message, intent);
            }else{
                //if there is an image
                //displaying a big notification
                getBitmapFromURL(imageUrl);

            }
        } catch (Exception e) {
            Log.e(TAG, "Exception: " + e.getMessage());
        }
    }
}



private void getBitmapFromURL(String strURL) {
    try {
        URL url = new URL(strURL);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setDoInput(true);
        connection.connect();
        InputStream input = connection.getInputStream();
        Bitmap myBitmap = BitmapFactory.decodeStream(input);
        mNotificationManager.showBigNotification(title, message, myBitmap, intent);
    } catch (IOException e) {
        e.printStackTrace();

    }
}