1.引入netty依赖

<dependencies>
<dependency><groupId>io.netty</groupId><artifactId>netty-all</artifactId><version>4.1.92.Final</version>
</dependency>
</dependencies>

2.准备一个服务端ChatServer和一个服务端处理器ChatServerHandler和若干个客户端ChatClient(有几个用户设置几个)和一个客户端处理器ChatClientHandler

服务端
public class ChatServer {public static void main(String[] args) {// 新建两个事件循环组,bossGroup 用于监听客户端的连接请求，将连接请求发送给 workerGroup 用于处理客户端连接的数据读写NioEventLoopGroup bossGroup = new NioEventLoopGroup();NioEventLoopGroup workGroup = new NioEventLoopGroup();ServerBootstrap serverBootstrap = new ServerBootstrap();serverBootstrap.group(bossGroup, workGroup);serverBootstrap.channel(NioServerSocketChannel.class);serverBootstrap.childHandler(new ChannelInitializer<NioSocketChannel>() {@Overrideprotected void initChannel(NioSocketChannel ch) throws Exception {ch.pipeline().addLast(new StringEncoder(CharsetUtil.UTF_8));ch.pipeline().addLast(new StringDecoder(CharsetUtil.UTF_8));ch.pipeline().addLast(new ChatServerHandler());}});// 服务端绑定9000端口serverBootstrap.bind(9000);}public void test(){NioEventLoopGroup bossGroup = new NioEventLoopGroup();NioEventLoopGroup workGroup = new NioEventLoopGroup();ServerBootstrap serverBootstrap = new ServerBootstrap();serverBootstrap.group(bossGroup,workGroup);serverBootstrap.channel(NioServerSocketChannel.class);serverBootstrap.childHandler(new ChannelInitializer<NioSocketChannel>() {@Overrideprotected void initChannel(NioSocketChannel nioSocketChannel) throws Exception {nioSocketChannel.pipeline().addLast(new StringEncoder(CharsetUtil.UTF_8));nioSocketChannel.pipeline().addLast(new StringDecoder(CharsetUtil.UTF_8));nioSocketChannel.pipeline().addLast(new ChatServerHandler());}});serverBootstrap.bind(9001);}
}

服务端处理器

public class ChatServerHandler extends ChannelInboundHandlerAdapter {// 创建一个list集合存储连接上的所有客户端channelprivate static List<Channel> channels = new ArrayList<>();// 当有客户端连接上服务端,底层会调用此方法，执行此方法的逻辑// 这里大概的处理逻辑是:先添加新客户端channel到集合中，然后循环遍历list集合// 然后根据不同的channel发送不同的系统消息@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {Channel channel = ctx.channel();channels.add(channel);channels.forEach(ch -> {if (ch == channel) {channel.writeAndFlush("恭喜您，上线成功");} else {ch.writeAndFlush("系统消息:[" + ch.remoteAddress() + "]客户端已上线");}});System.out.println("客户端[" + channel.remoteAddress() + "]请求连接");}// 当有客户端连断开连接,底层会调用此方法，执行此方法的逻辑// 这里大概的处理逻辑是:然后循环遍历list集合,找到已断开连接的channel并删除// 向集合内的channel发送系统消息@Overridepublic void channelInactive(ChannelHandlerContext ctx) throws Exception {Channel channel = ctx.channel();Iterator<Channel> iterator = channels.iterator();while (iterator.hasNext()) {Channel ch = iterator.next();if (ch == channel) {iterator.remove();}ch.writeAndFlush("系统消息:[" + channel.remoteAddress() + "]客户端已下线");}System.out.println("客户端[" + channel.remoteAddress() + "]断开连接");}// 当有客户端发送消息到服务端,底层会调用此方法，执行此方法的逻辑// 这里大概的处理逻辑是:循环遍历向集合中的channel(除发送消息的客户端)发送消息@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {Channel channel = ctx.channel();SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");Date date = new Date(System.currentTimeMillis());String now = formatter.format(date);System.out.println(now+"收到用户[" + channel.remoteAddress() + "]发来的消息:" + msg.toString());channels.forEach(ch -> {if (ch != channel) {ch.writeAndFlush("消息时间:" + now + " 用户[" + channel.remoteAddress() + "]说:" + msg.toString());}});}//异常触发@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {cause.printStackTrace();ctx.close();}
}

客户端

public class ChatClient {public static void main(String[] args) throws InterruptedException {NioEventLoopGroup workGroup = new NioEventLoopGroup();Bootstrap bootstrap = new Bootstrap();bootstrap.group(workGroup);bootstrap.channel(NioSocketChannel.class);// 设置处理器bootstrap.handler(new ChannelInitializer<NioSocketChannel>() {@Overrideprotected void initChannel(NioSocketChannel ch) throws Exception {// 将字符串编解码器及客户端处理器添加到pipeline中ch.pipeline().addLast(new StringDecoder(CharsetUtil.UTF_8));ch.pipeline().addLast(new StringEncoder(CharsetUtil.UTF_8));ch.pipeline().addLast(new ChatClientHandler());}});// 连接服务端ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 9000);channelFuture.sync();// 获取客户端输入的内容，并发送至服务端(因为添加了字符串编解码器，所以此处可以直接发送字符串)Scanner scanner = new Scanner(System.in);while (scanner.hasNextLine()) {channelFuture.channel().writeAndFlush(scanner.nextLine());}}
}

客户端处理器

public class ChatClientHandler extends ChannelInboundHandlerAdapter {@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {System.out.println(msg.toString());}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {cause.printStackTrace();ctx.close();}
}

如果需要多个客户端用户,将客户端多复制几个就可以了.

启动时先启动服务端再启动客户端