Netty入门之创建Maven多模块依赖项目

新学Netty，编译运行时踩了一些坑，记录在此。
essential netty in action中有一个入门demo，EchoServer and EchoClient，用于Netty入门的小demo。
(Essential Netty in Action)

EchoClient主要功能

1、启动客户端，发起连接

public class Client {
   
    private final String host;
    private final int port;

    public Client(String host, int port) {
        this.host = host;
        this.port = port;
    }

    public void start() throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();
        try{
            Bootstrap b = new Bootstrap();
            b.group(group)
                .channel(NioSocketChannel.class)
                .remoteAddress(new InetSocketAddress(host,port))
                .handler(new ChannelInitializer<SocketChannel>() {
                @Override
                public void initChannel(SocketChannel ch) 
                            throws Exception {
                    ch.pipeline().addLast(new ClientHandler());
                }
            });
            ChannelFuture f = b.connect().sync();

            f.channel().closeFuture().sync();
        }finally {
            group.shutdownGracefully().sync();
        }
    }

    public static void main(String[] args) throws Exception {
        if(args.length != 2){
            System.err.println(
                    "Usage :" + Client.class.getSimpleName()+
                    "<host><port>"
                    );
            return;
        }

        final String host = args[0];
        final int port = Integer.parseInt(args[1]);

        new Client(host,port).start();
    }

}

2、ClientHandler处理返回到客户端的数据

class ClientHandler extends SimpleChannelInboundHandler<ByteBuf>{
   

    @Override
    public void channelActive(ChannelHandlerContext ctx){
        ctx.writeAndFlush(Unpooled.copiedBuffer("Netty rocks!",CharsetUtil.UTF_8));
    }
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, ByteBuf in) throws Exception {
        System.out.println("Client received: "+in.toString(CharsetUtil.UTF_8)); 
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx,
                    Throwable cause) {
        cause.printStackTrace();
        ctx.close();
    }


}

EchoServer主要功能

1、启动服务端，监听连接请求

public class EchoServer {
   
    public void bind(int port) throws Exception {