问题是，当我将jar文件放入plugins文件夹并运行服务器时，我总是从控制台收到以下消息： Enabled plugin FirstCommand version 1.0-SNAPSHOT by null 我的代码由两个类组成：

public final class FirstCommand extends Plugin {

    @Override
    public void onEnable() {
        // Plugin startup logic
        getLogger().info("has loaded");
        getProxy().getPluginManager().registerCommand(this, new PingCommand());
    }

    @Override
    public void onDisable() {
        // Plugin shutdown logic
    }
}

和

public class PingCommand extends Command {

    public PingCommand() {
        super("ping");
    }

    @Override
    public void execute(CommandSender sender, String[] args) {
        if (sender instanceof ProxiedPlayer) {
            ProxiedPlayer player = (ProxiedPlayer) sender;
            int ping = player.getPing();
            player.sendMessage(new TextComponent(ChatColor.GRAY + "Your ping is: " + ChatColor.GREEN + ping));
        }
    }
}

bungee.yml : 
name: FirstCommand
version: ${project.version}
main: org.example.firstcommand.FirstCommand