JDA API中ListenerAdapter实例内存地址异常？/info命令无响应排查

刚接触JDA API，尝试开发/info命令时遇到机器人无响应的问题，调试发现InfoCommand的handle方法从未被调用。已知：

• InfoCommand已初始化并添加到CommandManager中
• CommandManager的onMessageReceived方法在消息发送时会被触发
• 触发onMessageReceived时，CommandManager的commands集合为空，且此时的CommandManager实例和初始化时的不是同一个

涉及代码： #

InfoCommand类

public class InfoCommand extends Command {
    public InfoCommand(String name) {
        super(name);
    }
    @Override
    public void handle(MessageReceivedEvent event, String... params) {
        EmbedBuilder builder = new EmbedBuilder();
        builder.setTitle("Test Title");
        builder.setDescription("Test Description" );
        builder.setFooter("Created by t0gepi");
        builder.setColor(0xf45642);
        event.getChannel().sendTyping().queue();
        event.getChannel().sendMessageEmbeds(builder.build()).queue();
    }
}

Main类

public class Main {
    public static JDA jda;

    public static void main(String[] args) throws LoginException {
        ResourceManager.init();
        jda = JDABuilder.createDefault(ResourceManager.getProperty("discord.bottoken")).build();
        jda.getPresence().setStatus(OnlineStatus.IDLE);
        jda.getPresence().setActivity(Activity.playing("Sleeping"));
        try {
            jda.awaitReady();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        CommandManager commandManager = new CommandManager();
        commandManager.addCommand(new InfoCommand("info"));
        jda.addEventListener(new CommandManager());
    }
}

CommandManager类

public class CommandManager extends ListenerAdapter {

    private Set<Command> commands;

    public CommandManager(){
        this.commands = new HashSet<>();
    }

    public void addCommand(Command command){
        commands.add(command);
    }

    @Override
    public void onMessageReceived(@NotNull MessageReceivedEvent event) {
        String[] msg = event.getMessage().getContentRaw().split(" ");
        String prefix = ResourceManager.getProperty("command.prefix");
        String[] params = null;
        if(!msg[0].startsWith(prefix)){
            return;
        }
        if(msg.length > 1){
            params = Arrays.copyOfRange(msg,1,msg.length);
        }
        Iterator<Command> iterator = commands.iterator();
        Command command;
        while(iterator.hasNext()){
            command = iterator.next();
            if(command.getAliases().stream().anyMatch(alias -> msg[0].equalsIgnoreCase(prefix + alias))){
                command.handle(event, params);
                return;
            }
        }
        // Do nothing here if command wasn't found.
    }
}

问题原因 #

Main类中创建了两个独立的CommandManager实例：

1. 第一个实例commandManager添加了InfoCommand
2. 第二个实例是通过new CommandManager()新建的，没有添加任何命令，却被注册为JDA的事件监听器

当消息事件触发时，JDA调用的是第二个空实例的onMessageReceived方法，自然找不到对应的命令，导致handle方法不执行。

解决方案 #

修改Main类的代码，将已经添加了命令的那个CommandManager实例注册为JDA监听器，而非新建实例：

public class Main {
    public static JDA jda;

    public static void main(String[] args) throws LoginException {
        ResourceManager.init();
        jda = JDABuilder.createDefault(ResourceManager.getProperty("discord.bottoken")).build();
        jda.getPresence().setStatus(OnlineStatus.IDLE);
        jda.getPresence().setActivity(Activity.playing("Sleeping"));
        try {
            jda.awaitReady();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        CommandManager commandManager = new CommandManager();
        commandManager.addCommand(new InfoCommand("info"));
        // 注册已添加命令的实例，而非新建
        jda.addEventListener(commandManager);
    }
}

内容的提问来源于stack exchange，提问作者smilly