實現以下功能：

• 1，一個客戶端上線/下線，通知所有的用戶。

• 2，一個客戶端發送消息，廣播所有的客戶端。

server端代碼

• 1，Server.java

public class Server {

    public static void main(String... arg) throws Exception {

        //負責接收客戶端連接
        NioEventLoopGroup boss = new NioEventLoopGroup();

        //負責處理客戶端連接
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();


        try {
            ServerBootstrap bootstrap = new ServerBootstrap();
            bootstrap.group(boss, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .handler(new LoggingHandler(LogLevel.INFO))
                    .childHandler(new ServerChatinitlizer());

            //綁定端口號
            ChannelFuture channelFuture = bootstrap.bind(8899).sync();
            channelFuture.channel().closeFuture().sync();

        } finally {
            boss.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }

    }
}

• 2,ServerChatinitlizer.java

public class ServerChatinitlizer extends ChannelInitializer<SocketChannel> {

    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();

        //編碼解碼器

        // 換行分割解碼器 \r\n
        pipeline.addLast(new DelimiterBasedFrameDecoder(4096, Delimiters.lineDelimiter()));

        pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
        pipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));

        //自己的處理器
        pipeline.addLast(new ServerChatHandler());


    }
}

• 3,ServerChatHandler.java

/**
 * 客戶端上線/下線 提示所有的人
 * 發送消息發給所有的人
 */
public class ServerChatHandler extends SimpleChannelInboundHandler<String> {

    //保存已建立所用用戶的實例
    private static ChannelGroup channelGroup = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);


    //接收客戶端發送的消息
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        Channel channel = ctx.channel();

        channelGroup.forEach(ch -> {
            if (ch == channel) {  //表示自己
                channel.writeAndFlush("[自己]  "  + msg + "\n");
            } else {
                ch.writeAndFlush(ch.remoteAddress() + "  發送的消息  " + msg + "\n");
            }
        });

    }

    //客戶端與服務器端建立好連接
    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        System.out.println("handlerAdded");
        Channel channel = ctx.channel();
        //廣播已連接的客戶端 有新的用戶上線
        channelGroup.writeAndFlush("[服務器]-" + channel.remoteAddress() +" 上線\n");
        // 保存用戶實例
        channelGroup.add(channel);

    }

    //鏈接斷開
    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {

        System.out.println("handlerRemoved");
        Channel channel = ctx.channel();
        //廣播已連接的客戶端 用戶下線
        channelGroup.writeAndFlush("[服務器]-" + channel.remoteAddress() + " 下線\n");

        //channelGroup 會自動 剔除已斷開的用戶連接

    }


    //處于活動狀態
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        System.out.println("[服務器]-" + channel.remoteAddress() +" 上線\n");
    }


    //下線
    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        super.channelInactive(ctx);
        Channel channel = ctx.channel();
        System.out.println("[服務器]-" + channel.remoteAddress() +  " 下線\n");
    }


    // 發生異常關閉連接
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

client端代碼

• 1,Client.java

public class Client {
    public static void main(String... arg) throws Exception {
        EventLoopGroup eventLoopGroup = new NioEventLoopGroup();

        try {

            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(eventLoopGroup).channel(NioSocketChannel.class)
                    .handler(new ChatInitializer());

           Channel channel = bootstrap.connect("127.0.0.1",8899).sync().channel();

            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            while (true){
                channel.writeAndFlush(br.readLine()+"\r\n");
            }

        } finally {
            eventLoopGroup.shutdownGracefully();
        }

    }
}

• 2, ChatInitializer.java

public class ChatInitializer 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 StringEncoder(CharsetUtil.UTF_8));
        pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));

        pipeline.addLast(new ChatHandler());

    }
}

• 3, ChatHandler

public class ChatHandler extends SimpleChannelInboundHandler<String> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {

        System.out.println(" 接收到數據 " + msg);

    }
}