startForeground falla después de actualizar a Android 8.1

Funciona correctamente en Andorid 8.1:

Muestra actualizada (sin ningún código obsoleto):

public NotificationBattery(Context context) {
    this.mCtx = context;

    mBuilder = new NotificationCompat.Builder(context, CHANNEL_ID)
            .setContentTitle(context.getString(R.string.notification_title_battery))
            .setSmallIcon(R.drawable.ic_launcher)
            .setVisibility(NotificationCompat.VISIBILITY_PUBLIC)
            .setChannelId(CHANNEL_ID)
            .setOnlyAlertOnce(true)
            .setPriority(NotificationCompat.PRIORITY_MAX)
            .setWhen(System.currentTimeMillis() + 500)
            .setGroup(GROUP)
            .setOngoing(true);

    mRemoteViews = new RemoteViews(context.getPackageName(), R.layout.notification_view_battery);

    initBatteryNotificationIntent();

    mBuilder.setContent(mRemoteViews);

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

    if (AesPrefs.getBooleanRes(R.string.SHOW_BATTERY_NOTIFICATION, true)) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel channel = new NotificationChannel(CHANNEL_ID, context.getString(R.string.notification_title_battery),
                    NotificationManager.IMPORTANCE_DEFAULT);
            channel.setShowBadge(false);
            channel.setSound(null, null);
            mNotificationManager.createNotificationChannel(channel);
        }
    } else {
        mNotificationManager.cancel(Const.NOTIFICATION_CLIPBOARD);
    }
}

Old snipped (es una aplicación diferente - no relacionada con el código anterior):

@Override
public int onStartCommand(Intent intent, int flags, final int startId) {
    Log.d(TAG, "onStartCommand");

    String CHANNEL_ONE_ID = "com.kjtech.app.N1";
    String CHANNEL_ONE_NAME = "Channel One";
    NotificationChannel notificationChannel = null;
    if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
        notificationChannel = new NotificationChannel(CHANNEL_ONE_ID,
                CHANNEL_ONE_NAME, IMPORTANCE_HIGH);
        notificationChannel.enableLights(true);
        notificationChannel.setLightColor(Color.RED);
        notificationChannel.setShowBadge(true);
        notificationChannel.setLockscreenVisibility(Notification.VISIBILITY_PUBLIC);
        NotificationManager manager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
        manager.createNotificationChannel(notificationChannel);
    }

    Bitmap icon = BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher);
    Notification notification = new Notification.Builder(getApplicationContext())
            .setChannelId(CHANNEL_ONE_ID)
            .setContentTitle(getString(R.string.obd_service_notification_title))
            .setContentText(getString(R.string.service_notification_content))
            .setSmallIcon(R.mipmap.ic_launcher)
            .setLargeIcon(icon)
            .build();

    Intent notificationIntent = new Intent(getApplicationContext(), MainActivity.class);
    notificationIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_SINGLE_TOP);
    notification.contentIntent = PendingIntent.getActivity(getApplicationContext(), 0, notificationIntent, 0);

    startForeground(START_FOREGROUND_ID, notification);

    return START_STICKY;
}

(Incluye Android 9.0 Pie (API 28) update) Solución simple en Java

En el método onCreate() de su Service

@Override
public void onCreate(){
    super.onCreate();
    if (Build.VERSION.SDK_INT > Build.VERSION_CODES.O)
        startMyOwnForeground();
    else
        startForeground(1, new Notification());
}

Define tu propio primer plano aquí

private void startMyOwnForeground(){
    String NOTIFICATION_CHANNEL_ID = "com.example.simpleapp";
    String channelName = "My Background Service";
    NotificationChannel chan = new NotificationChannel(NOTIFICATION_CHANNEL_ID, channelName, NotificationManager.IMPORTANCE_NONE);
    chan.setLightColor(Color.BLUE);
    chan.setLockscreenVisibility(Notification.VISIBILITY_PRIVATE);
    NotificationManager manager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
    assert manager != null;
    manager.createNotificationChannel(chan);

    NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this, NOTIFICATION_CHANNEL_ID);
    Notification notification = notificationBuilder.setOngoing(true)
            .setSmallIcon(R.drawable.icon_1)
            .setContentTitle("App is running in background")
            .setPriority(NotificationManager.IMPORTANCE_MIN)
            .setCategory(Notification.CATEGORY_SERVICE)
            .build();
    startForeground(2, notification);
}

ACTUALIZACIÓN: ANDORID 9.0 PIE (API 28)

Las aplicaciones dirigidas a Android 9 (nivel de API 28) o superior y que usan servicios en primer plano deben solicitar el permiso FOREGROUND_SERVICE. Este es un permiso normal, por lo que el sistema lo otorga automáticamente a la aplicación solicitante.

Si una aplicación que se dirige al nivel de API 28 o superior intenta crear un servicio en primer plano sin solicitar FOREGROUND_SERVICE, el sistema lanza una SecurityException.

Simplemente agregue este permiso en su archivo AndroidManifest.xml.

<uses-permission android:name="android.permission.FOREGROUND_SERVICE" />

La primera respuesta es genial solo para aquellas personas que conocen kotlin, para aquellos que todavía usan java aquí traduzco la primera respuesta

 public Notification getNotification() {
        String channel;
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O)
            channel = createChannel();
        else {
            channel = "";
        }
        NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(this, channel).setSmallIcon(android.R.drawable.ic_menu_mylocation).setContentTitle("snap map fake location");
        Notification notification = mBuilder
                .setPriority(PRIORITY_LOW)
                .setCategory(Notification.CATEGORY_SERVICE)
                .build();


        return notification;
    }

    @NonNull
    @TargetApi(26)
    private synchronized String createChannel() {
        NotificationManager mNotificationManager = (NotificationManager) this.getSystemService(Context.NOTIFICATION_SERVICE);

        String name = "snap map fake location ";
        int importance = NotificationManager.IMPORTANCE_LOW;

        NotificationChannel mChannel = new NotificationChannel("snap map channel", name, importance);

        mChannel.enableLights(true);
        mChannel.setLightColor(Color.BLUE);
        if (mNotificationManager != null) {
            mNotificationManager.createNotificationChannel(mChannel);
        } else {
            stopSelf();
        }
        return "snap map channel";
    } 

En mi caso, es porque intentamos publicar una notificación sin especificar el NotificationChannel:

public static final String NOTIFICATION_CHANNEL_ID_SERVICE = "com.mypackage.service";
public static final String NOTIFICATION_CHANNEL_ID_TASK = "com.mypackage.download_info";

public void initChannel(){
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        NotificationManager nm = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
        nm.createNotificationChannel(new NotificationChannel(NOTIFICATION_CHANNEL_ID_SERVICE, "App Service", NotificationManager.IMPORTANCE_DEFAULT));
        nm.createNotificationChannel(new NotificationChannel(NOTIFICATION_CHANNEL_ID_INFO, "Download Info", NotificationManager.IMPORTANCE_DEFAULT));
    }
}

El mejor lugar para poner el código anterior es en el método onCreate() en la clase Application, por lo que solo necesitamos declararlo de una vez por todas:

public class App extends Application {

    @Override
    public void onCreate() {
        super.onCreate();
        initChannel();
    }
}

Después de configurar esto, podemos usar la notificación con el channelId que acabamos de especificar:

Intent i = new Intent(this, MainActivity.class);
i.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_SINGLE_TOP);
PendingIntent pi = PendingIntent.getActivity(this, 0, i, PendingIntent.FLAG_UPDATE_CURRENT);
NotificationCompat.Builder builder = new NotificationCompat.Builder(this, NOTIFICATION_CHANNEL_ID_INFO);
            .setContentIntent(pi)
            .setWhen(System.currentTimeMillis())
            .setContentTitle("VirtualBox.exe")
            .setContentText("Download completed")
            .setSmallIcon(R.mipmap.ic_launcher);

Entonces, podemos usarlo para publicar una notificación:

int notifId = 45;
NotificationManager nm = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
nm.notify(notifId, builder.build());

Si desea usarlo como notificación del servicio en primer plano:

startForeground(notifId, builder.build());

Esto funcionó para mí. En mi clase de servicio, creé el canal de notificación para Android 8.1 como se muestra a continuación:

public class Service extends Service {

    public static final String NOTIFICATION_CHANNEL_ID_SERVICE = "com.package.MyService";
    public static final String NOTIFICATION_CHANNEL_ID_INFO = "com.package.download_info";

    @Override
    public void onCreate() {

        super.onCreate();
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationManager nm = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
            nm.createNotificationChannel(new NotificationChannel(NOTIFICATION_CHANNEL_ID_SERVICE, "App Service", NotificationManager.IMPORTANCE_DEFAULT));
            nm.createNotificationChannel(new NotificationChannel(NOTIFICATION_CHANNEL_ID_INFO, "Download Info", NotificationManager.IMPORTANCE_DEFAULT));
        } else {
            Notification notification = new Notification();
            startForeground(1, notification);
        }
    }
}

Nota: Cree el canal donde está creando la Notificación para Build.VERSION.SDK_INT >= Build.VERSION_CODES.O