几百行代码，实现了微信群聊，神奇！

public class GroupChatServer {

    private int port;

    public GroupChatServer(int port) {
        this.port = port;
    }

    /**
     * 编写run方法，处理客户端的请求
     */
    public void run() throws  Exception{

        //创建两个线程组
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        //8个NioEventLoop
        EventLoopGroup workerGroup = new NioEventLoopGroup(8);
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    // BACKLOG用于构造服务端套接字ServerSocket对象，标识当服务器请求处理线程全满时，
                    // 用于临时存放已完成三次握手的请求的队列的最大长度。如果未设置或所设置的值小于1，Java将使用默认值50。
                    .option(ChannelOption.SO_BACKLOG, 128)
                    //是否启用心跳保活机制。在双方TCP套接字建立连接后（即都进入ESTABLISHED状态）
                    // 并且在两个小时左右上层没有任何数据传输的情况下，这套机制才会被激活。
                    .childOption(ChannelOption.SO_KEEPALIVE, true)
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            //获取到pipeline
                            ChannelPipeline pipeline = ch.pipeline();
                            //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 GroupChatServerHandler());
                        }
                    });
            System.out.println("netty 服务器启动");
            ChannelFuture channelFuture = b.bind(port).sync();
            //监听关闭
            channelFuture.channel().closeFuture().sync();
        }finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
    
    public static void main(String[] args) throws Exception {
        new GroupChatServer(7000).run();
    }
}

public class GroupChatServerHandler 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");

    /**
     * 将当前channel 加入到  channelGroup
     * 表示连接建立，一旦连接，第一个被执行
     * @param ctx
     * @throws Exception
     */
    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        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，
        我们不需要自己遍历
         */
        channelGroup.writeAndFlush("[客户端]" + channel.remoteAddress() + " 加入聊天" + sdf.format(new java.util.Date()) + " n");
        channelGroup.add(channel);
    }

    /**
     * 断开连接, 将xx客户离开信息推送给当前在线的客户
     * @param ctx
     * @throws Exception
     */
    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        channelGroup.writeAndFlush("[客户端]" + channel.remoteAddress() + " 离开了n");
        System.out.println("channelGroup size" + channelGroup.size());
    }

    /**
     * 表示channel 处于活动状态, 提示 xx上线
     * @param ctx
     * @throws Exception
     */
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println(ctx.channel().remoteAddress() + " 上线了~");
    }

    /**
     * 表示channel 处于不活动状态, 提示 xx离线了
     * @param ctx
     * @throws Exception
     */
    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        System.out.println(ctx.channel().remoteAddress() + " 离线了~");
    }

    /**
     * 读取数据
     * @param ctx
     * @param msg
     * @throws Exception
     */
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        //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]" + 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) throws Exception {
        //关闭通道
        ctx.close();
    }
}

public class GroupChatClient {

    private final String host;

    private final int port;

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

    public void run() throws Exception{
        EventLoopGroup group = new NioEventLoopGroup();
        try {
        Bootstrap bootstrap = new Bootstrap()
            .group(group)
            .channel(NioSocketChannel.class)
            .handler(new ChannelInitializer<SocketChannel>() {
                @Override
                protected void initChannel(SocketChannel ch) throws Exception {
                    //得到pipeline
                    ChannelPipeline pipeline = ch.pipeline();
                    //加入相关handler
                    pipeline.addLast("decoder", new StringDecoder());
                    pipeline.addLast("encoder", new StringEncoder());
                    //加入自定义的handler
                    pipeline.addLast(new GroupChatClientHandler());
                }
            });
        ChannelFuture channelFuture = bootstrap.connect(host, port).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 + "rn");
            }
        }finally {
            group.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        new GroupChatClient("127.0.0.1", 7000).run();
    }
}

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

给个[在看]，是对IT老哥最大的支持