Discord Bot 不响应我们的命令

Question

我按照 YouTube 上的视频教程制作了一个 Discord 机器人。我被困在机器人不回复命令的部分。

如果有人知道如何解决这个问题，我将不胜感激。

这是源代码：

Night.java：

package ch.teraflash;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

import javax.security.auth.login.LoginException;

import ch.teraflash.listener.CommandListener;
import net.dv8tion.jda.api.OnlineStatus;
import net.dv8tion.jda.api.entities.Activity;
import net.dv8tion.jda.api.sharding.DefaultShardManagerBuilder;
import net.dv8tion.jda.api.sharding.ShardManager;

public class Night {

    public ShardManager shardMan;
    
    public static void main(String[] args)  {
        try {
            new Night();
        } catch (LoginException e) {
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
        }
    }

    public Night() throws LoginException, IllegalArgumentException {

        DefaultShardManagerBuilder builder = new DefaultShardManagerBuilder();
        builder.setToken("XXX");
        
        builder.setActivity(Activity.playing("die Nacht."));
        builder.setStatus(OnlineStatus.ONLINE);
                
        builder.addEventListeners(new CommandListener());
        
        shardMan = builder.build();
        System.out.println("Bot online.");
        
        shutdown();
    }
    
    public void shutdown() {
        
        new Thread(() -> {
            
            String line = "";
            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
            try {
                while((line = reader.readLine()) != null) {
                    
                    if(line.equalsIgnoreCase("exit")) {
                        if(shardMan != null) {
                            shardMan.setStatus(OnlineStatus.OFFLINE);
                            shardMan.shutdown();
                            System.out.println("Bot offline.");
                        }
                        
                        reader.close();
                    }
                    else {
                        System.out.println("Use 'exit' to shutdown.");
                    }
                }
            }catch (IOException e) {
                e.printStackTrace();
            }
            
        }).start();
    }
}

CommandListener.java:

package ch.teraflash.listener;

import net.dv8tion.jda.api.entities.ChannelType;
import net.dv8tion.jda.api.entities.TextChannel;
import net.dv8tion.jda.api.events.message.MessageReceivedEvent;
import net.dv8tion.jda.api.hooks.ListenerAdapter;

public class CommandListener extends ListenerAdapter {
    
    @Override
    public void onMessageReceived(MessageReceivedEvent event) {
        
        String message = event.getMessage().getContentDisplay();
        
        if(event.isFromType(ChannelType.TEXT)) {
            TextChannel channel = event.getTextChannel();
                    
            //!tut arg0 arg1 arg 2 ...
            if(message.startsWith("!tut ")) {
                String[] args = message.substring(5).split(" ");
                
                if(args.length == 1) {
                    if(args[0].equalsIgnoreCase("Hallo")) {
                        channel.sendMessage("Hallo " + event.getMember().getAsMention() + "! ").queue();
                        
                    }
                }
                
            }
            
        }
        
    }