CreateNotification.java

private void createNotification(String title, String message) {
        int num = (int) System.currentTimeMillis();
        Intent resultIntent = new Intent(PusherService.this, MainActivity.class);
        resultIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        resultIntent.addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);

        PendingIntent resultPendingIntent =
                PendingIntent.getActivity(this, num, resultIntent, PendingIntent.FLAG_UPDATE_CURRENT);

        NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(this);
        mBuilder.setContentTitle(title)
                .setContentText(message)
                .setAutoCancel(true)
                .setSmallIcon(R.mipmap.ic_launcher)
                .setSound(Settings.System.DEFAULT_NOTIFICATION_URI)
                .setContentIntent(resultPendingIntent);

        NotificationManager mNotificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
            int importance = NotificationManager.IMPORTANCE_HIGH;
            NotificationChannel notificationChannel = new NotificationChannel("1", "Notifications", importance);
            notificationChannel.enableLights(true);
            notificationChannel.setLightColor(Color.RED);
            notificationChannel.enableVibration(true);
            notificationChannel.setVibrationPattern(new long[]{100L, 200L, 300L, 400L, 500L, 400L, 300L, 200L, 400L});
            mBuilder.setChannelId("1");
            mNotificationManager.createNotificationChannel(notificationChannel);
        }

        mNotificationManager.notify(num, mBuilder.build());
    }