服务端

ublic class MyChatServer {

    public static final int INET_PORT = 8888;
    public static void main(String[] args) throws Exception {
        EventLoopGroup boss = new NioEventLoopGroup();
        EventLoopGroup worker = new NioEventLoopGroup();
        ServerBootstrap serverBootstrap = new ServerBootstrap();
        try {
            serverBootstrap.group(boss, worker)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new MyChatServerInitializer());
            ChannelFuture future = serverBootstrap.bind(INET_PORT).sync();
            future.channel().closeFuture().sync();
        } finally {
            boss.shutdownGracefully();
            worker.shutdownGracefully();
        }
    }
}

public class MyChatServerInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        pipeline.addLast(new DelimiterBasedFrameDecoder(4096, Delimiters.lineDelimiter()));
        pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
        pipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));
        pipeline.addLast(new MyChatServerHandler());
    }
}

public class MyChatServerHandler extends SimpleChannelInboundHandler<String> {

    public static final String STRING = "\n";
    public static final String SEND_MSG = "发送的消息：";
    public static final String ITSELF = "【自己】";
    public static final String JOIN = "加入";
    public static final String LEFT = "离开";
    public static final String ON_LINE = " 上线";
    public static final String OFF_LINE = " 下线";
    public static final String SERVER = "【服务器】 - ";
    private static ChannelGroup channelGroup = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        Channel channel = ctx.channel();
        channelGroup.forEach(ch -> {
            if (channel != ch) {
                ch.writeAndFlush(channel.remoteAddress() + SEND_MSG + msg + "\n");
            } else {
                ch.writeAndFlush(ITSELF + msg + "\n");
            }
        });
    }

    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        channelGroup.writeAndFlush(SERVER + channel.remoteAddress() + JOIN + "\n");
        channelGroup.add(channel);
    }

    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        channelGroup.writeAndFlush(SERVER + channel.remoteAddress() + LEFT + STRING);
//        channelGroup.remove(channel); 不用显示调用
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        System.out.println(channel.remoteAddress() + ON_LINE + STRING);
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        System.out.println(channel.remoteAddress() + OFF_LINE + STRING);
    }

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

客户端

public class MyChatClient {
    public static void main(String[] args) throws Exception{
        EventLoopGroup group = new NioEventLoopGroup();
        Bootstrap bootstrap = new Bootstrap();
        try {
            bootstrap.group(group)
                    .channel(NioSocketChannel.class)
                    .handler(new MyChatClientInitializer());
            Channel channel = bootstrap.connect("localhost", 8888).sync().channel();

            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

            for (; ; ) {
                channel.writeAndFlush(br.readLine() + "\r\n");
            }

        } finally {
            group.shutdownGracefully();
        }
    }
}

public class MyChatClientInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        pipeline.addLast(new DelimiterBasedFrameDecoder(4096, Delimiters.lineDelimiter()));
        pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
        pipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));
        pipeline.addLast(new MyChatClientlHandler());
    }
}

public class MyChatClientlHandler extends SimpleChannelInboundHandler<String> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        System.out.println(msg);
    }
}