思路：客户端发送数据，服务端接收到数据之后发送给所有客户端。

服务端代码

还是基本分为三步：初始化启动对象，启动对象链式添加，绑定端口。主要业务放在handler里边。

    public static void main(String[] args) throws Exception {
        //创建主从reactor
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup(8);
        try {
            //初始化启动对象
            ServerBootstrap bootstrap = new ServerBootstrap();
            //往启动对象加属性
            bootstrap.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 1024)
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline pipeline = ch.pipeline();
                            //加入特殊分隔符分包解码器
                            //pipeline.addLast(new DelimiterBasedFrameDecoder(1024, Unpooled.copiedBuffer("_"
                            // .getBytes())));
                            //向pipeline加入解码器
                            pipeline.addLast("decoder", new StringDecoder());
                            //向pipeline加入编码器
                            pipeline.addLast("encoder", new StringEncoder());
                            //加入自己的业务处理handler
                            pipeline.addLast(new ChatServerHandler());
                        }
                    });
            System.out.println("server start ");
            ChannelFuture channelFuture = bootstrap.bind(9000).sync();
            //关闭通道
            channelFuture.channel().closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

服务端handler

注册一个全局通道组，如果有通道连接则注册进channelGroup ，然后遍历channel通知。如果通道断开，遍历通知。读取数据时，判断是否是自己管道发送的数据，之后做处理。如果发生异常，则断开连接。

public class ChatServerHandler extends SimpleChannelInboundHandler<String> {

    //GlobalEventExecutor.INSTANCE 是全局的事件执行器，是一个单例
    private static ChannelGroup channelGroup = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

    //表示 channel 处于就绪状态, 提示上线
    @Override
    public void channelActive(ChannelHandlerContext ctx) {
        Channel channel = ctx.channel();
        //将该客户加入聊天的信息推送给其它在线的客户端
        //该方法会将 channelGroup 中所有的 channel 遍历，并发送消息
        channelGroup.writeAndFlush("[ 客户端 ]" + channel.remoteAddress() + " 上线了 " + sdf.format(new
                java.util.Date()) + "\n");
        //将当前 channel 加入到 channelGroup
        channelGroup.add(channel);
        System.out.println(ctx.channel().remoteAddress() + " 上线了" + "\n");
    }

    //表示 channel 处于不活动状态, 提示离线了
    @Override
    public void channelInactive(ChannelHandlerContext ctx) {
        Channel channel = ctx.channel();
        //将客户离开信息推送给当前在线的客户
        channelGroup.writeAndFlush("[ 客户端 ]" + channel.remoteAddress() + " 下线了" + "\n");
        System.out.println(ctx.channel().remoteAddress() + " 下线了" + "\n");
        System.out.println("channelGroup size=" + channelGroup.size());
    }

    //读取数据
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) {
        //获取到当前 channel
        Channel channel = ctx.channel();
        //这时我们遍历 channelGroup, 根据不同的情况， 回送不同的消息
        channelGroup.forEach(ch -> {
            if (channel != ch) { //不是当前的 channel,转发消息
                ch.writeAndFlush("[ 客户端 ]" + channel.remoteAddress() + " 发送了消息：" + msg + "\n");
            } else {//回显自己发送的消息给自己
                ch.writeAndFlush("[ 自己 ]发送了消息：" + msg + "\n");
            }
        });
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        //关闭通道
        ctx.close();
    }
}

客户端

连接端口，并读取控制台字符，然后发送。

    public static void main(String[] args) throws Exception {
		
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(group)
                    .channel(NioSocketChannel.class)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline pipeline = ch.pipeline();
                            //pipeline.addLast(new DelimiterBasedFrameDecoder(1024, Unpooled.copiedBuffer("_"
                            // .getBytes())));
                            //向pipeline加入解码器
                            pipeline.addLast("decoder", new StringDecoder());
                            //向pipeline加入编码器
                            pipeline.addLast("encoder", new StringEncoder());
                            //加入自己的业务处理handler
                            pipeline.addLast(new ChatClientHandler());
                        }
                    });
            ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 9000).sync();
            //得到 channel
            Channel channel = channelFuture.channel();
            System.out.println("========" + channel.localAddress() + "========");
            //客户端需要输入信息， 创建一个扫描器
            Scanner scanner = new Scanner(System.in);
            while (scanner.hasNextLine()) {
                String msg = scanner.nextLine();
                //通过 channel 发送到服务器端
                channel.writeAndFlush(msg);
            }
        } finally {
            group.shutdownGracefully();
        }
    }

客户端handler

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