FCM 通知未显示

Question

所以我的通知系统无缘无故无法工作，我尝试了很多 stackoverflow 解决方案，但没有一个真正起作用。我思考了好几个小时，所以请帮忙！

这是 MessagingService.java 类：

public final class MessagingService extends FirebaseMessagingService {

    @Override
    public void onMessageReceived(@NonNull RemoteMessage remoteMessage) {
        super.onMessageReceived(remoteMessage);
        User user = new User(
                remoteMessage.getData().get(Constants.KEY_NAME),
                "",
                "",
                remoteMessage.getData().get(Constants.KEY_FCM_TOKEN),
                remoteMessage.getData().get(Constants.KEY_USER_ID)
        );

        String channelId = "chat_message";

        Intent intent = new Intent(this, ChatActivity.class);

        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
        intent.putExtra(Constants.KEY_USER, user);

        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent, 0);

        NotificationCompat.Builder builder = new NotificationCompat.Builder(this, channelId);

        builder.setSmallIcon(R.drawable.ic_notification);
        builder.setContentTitle(user.getName());
        builder.setContentText(remoteMessage.getData().get(Constants.KEY_MESSAGE));
        builder.setStyle(new NotificationCompat.BigTextStyle()
                .bigText(remoteMessage.getData().get(Constants.KEY_MESSAGE)));
        builder.setPriority(NotificationCompat.PRIORITY_HIGH);
        builder.setContentIntent(pendingIntent);
        builder.setAutoCancel(true);
        builder.addAction(R.drawable.ic_notification, "eee", pendingIntent);

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {

            CharSequence channelName = "Chat Message";
            String channelDescription = "Used for message notifications";

            NotificationChannel channel = new NotificationChannel("", "", NotificationManager.IMPORTANCE_DEFAULT);
            channel.setDescription(channelDescription);

            NotificationManager notificationChannel = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
            notificationChannel.createNotificationChannel(channel);
        }

        int id = ThreadLocalRandom.current().nextInt(100);

        NotificationManagerCompat notificationManagerCompat = NotificationManagerCompat.from(this);
        notificationManagerCompat.notify(id, builder.build());
    }
}

这是我的 AndroidManifest.xml：

        <service
            android:name=".firebase.MessagingService"
            android:exported="false">
            <intent-filter>
                <action android:name="com.google.firebase.MESSAGING_EVENT" />
            </intent-filter>
        </service>