1.MyChatServer.java

public class MyChatServer {
    public static void main(String[] args) {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup,workGroup).channel(NioServerSocketChannel.class).childHandler(new ChannelInitializer<SocketChannel>() {

                @Override
                protected void initChannel(SocketChannel sc) throws Exception {
                    ChannelPipeline pipeline = sc.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 TestMyChatServerHandler());
                }
            });
            ChannelFuture channelFuture  = serverBootstrap.bind(8989).sync();
            channelFuture.channel().closeFuture().sync();

        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            bossGroup.shutdownGracefully();
            workGroup.shutdownGracefully();
        }
    }
}

2.TestMyChatServerHandler.java

public class TestMyChatServerHandler extends SimpleChannelInboundHandler<String>{
    private static ChannelGroup channelGroup = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);
//    ChannelGroup 是获取到         所有的客户端        连接的channle 
    @Override
    protected void channelRead0(ChannelHandlerContext paramChannelHandlerContext, String msg) throws Exception {
        //当任意一个客户端连接上服务端时，就会执行的方法
        Channel channel = paramChannelHandlerContext.channel();
        channelGroup.forEach(ch -> {
            if(channel!=ch){
                ch.writeAndFlush(channel.remoteAddress()+"发送的消息"+msg+"\n");
            }else{
                ch.writeAndFlush("[自己]"+msg+"\n");
            }
        });
//    对上述ch -> 的解析代码    
//  channelGroup.forEach(new Consumer<Channel>() {
//            @Override
//            public void accept(Channel t) {
//                if(channel!=t){
//                    t.writeAndFlush(channel.remoteAddress()+"发送的消息"+msg+"\n");
//                }else{
//                    t.writeAndFlush("[自己]"+msg+"\n");
//                }
//            }
//        });    

    }
    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        channelGroup.writeAndFlush("[服务器]"+channel.remoteAddress()+"加入\n");
        channelGroup.add(channel);//这两句是先广播其他服务器，再加入自己
    }
    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        channelGroup.writeAndFlush("[服务器]"+channel.remoteAddress()+"退出\n");
//        channelGroup.remove(channel);实际上这句可以不用加，因为当连接断开后，会将channel自动断开
    }
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        System.out.println(channel.remoteAddress()+"上线了\n");
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        System.out.println(channel.remoteAddress()+"下线了\n");
    }

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

3.MyChatClient.java

public class MyChatClient {
    public static void main(String[] args) {
        EventLoopGroup eventLoopGroup = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(eventLoopGroup).channel(NioSocketChannel.class).handler(new ChannelInitializer<SocketChannel>() {

                @Override
                protected void initChannel(SocketChannel sc) throws Exception {
                    ChannelPipeline pipeline = sc.pipeline();
                    pipeline.addLast(new DelimiterBasedFrameDecoder(4096,Delimiters.lineDelimiter()));
                    pipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));
                    pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
                    pipeline.addLast(new TestMyChatClientHandler());
                }
            });
            Channel channel  = bootstrap.connect("localhost",8989).sync().channel();
            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

            for(;;){
               channel.writeAndFlush(reader.readLine()+"\r\n");
            }//创造死循环，读取键盘输入的信息
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            eventLoopGroup.shutdownGracefully();
        }
    }
}

4.TestMyChatClientHandler.java

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

5.TcpHandler拦截器解答

DelimiterBasedFrameDecoder(4096,Delimiters.lineDelimiter());     //4096是maxFrameLength

DelimiterBasedFrameDecoder用来解决以特殊符号作为消息结束符的粘包问题，本例中用到的是”\r\n”和“\n”。

ChannelGroup 是获取到所有的客户端连接的channle 。故可以进行广播处理。