import io.netty.channel.ChannelInitializer;

 import io.netty.channel.ChannelPipeline;

 import io.netty.channel.socket.SocketChannel;

 import io.netty.handler.codec.DelimiterBasedFrameDecoder;

 import io.netty.handler.codec.Delimiters;

 import io.netty.handler.codec.string.StringDecoder;

 import io.netty.handler.codec.string.StringEncoder;

 import io.netty.util.CharsetUtil;

 public class MyChatServerInitlalizer extends ChannelInitializer<SocketChannel> {

     @Override

     protected void initChannel(SocketChannel ch) throws Exception {

         ChannelPipeline pipeline = ch.pipeline();

         //解码器，根据分隔符来分割

         pipeline.addLast(new DelimiterBasedFrameDecoder(4096, Delimiters.lineDelimiter()));

         pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));//编码

         pipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));//解码

         pipeline.addLast(new MyChatServerHandler());

     }

 }

 import io.netty.channel.Channel;

 import io.netty.channel.ChannelHandlerContext;

 import io.netty.channel.SimpleChannelInboundHandler;

 import io.netty.channel.group.ChannelGroup;

 import io.netty.channel.group.DefaultChannelGroup;

 import io.netty.util.concurrent.GlobalEventExecutor;

 public class MyChatServerHandler extends SimpleChannelInboundHandler<String> {

     //这个对象可以获取到所有的channel

     private static ChannelGroup channelGroup = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);

     @Override

     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {

         cause.printStackTrace();

         ctx.close();

     }

     @Override

     protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {

         Channel channel = ctx.channel();

         channelGroup.forEach(ch -> {

             System.out.println("ii");

             if(ch != channel) {

                 System.out.println("othor");

                 ch.writeAndFlush(channel.remoteAddress() + "发送的消息：" + msg + "\n");//发送消息出去的时候，这个\n,一定不能丢，不然发不出去

             } else {

                 ch.writeAndFlush( "自己： " + msg + "\n");

             }

         });

         //服务器接收到消息，相所有客户端 发送 消息

         System.out.println("接收到 " + channel.remoteAddress() +" 客户端的消息：" + msg);

 //        //发送给其他客户端

 //        ctx.writeAndFlush("msg");

     }

     @Override

     public void handlerAdded(ChannelHandlerContext ctx) throws Exception {

         Channel channel = ctx.channel();//获取到连接

         //告诉已有的其他连接

         channelGroup.writeAndFlush("[服务器] - " + channel.remoteAddress() + " - 加入\n");

         //再加入

         channelGroup.add(channel);//把channel加到channelGroup

     }

     @Override

     public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {

         Channel channel = ctx.channel();

         channelGroup.writeAndFlush("[服务器] - " + channel.remoteAddress() + "已离开\n");

 //        channelGroup.remove(channel);//netty会自动将已经失去连接的channel,从channelGroup 中移除

     }

     @Override

     public void channelActive(ChannelHandlerContext ctx) throws Exception {

         Channel channel = ctx.channel();

         System.out.println(channel.remoteAddress() + "上线了！");

     }

     @Override

     public void channelInactive(ChannelHandlerContext ctx) throws Exception {

         Channel channel = ctx.channel();

         System.out.println(channel.remoteAddress() + "下线了！");

     }

 }

 import io.netty.bootstrap.Bootstrap;

 import io.netty.channel.Channel;

 import io.netty.channel.ChannelFuture;

 import io.netty.channel.EventLoopGroup;

 import io.netty.channel.nio.NioEventLoopGroup;

 import io.netty.channel.socket.nio.NioSocketChannel;

 import java.io.BufferedReader;

 import java.io.IOException;

 import java.io.InputStreamReader;

 public class MyChatClient {

     public static void main(String[] args) throws InterruptedException, IOException {

         //客户端只需要一个

         EventLoopGroup eventLoopGroup = new NioEventLoopGroup();

         try{

             Bootstrap bootstrap = new Bootstrap();

             bootstrap.group(eventLoopGroup)

                     .channel(NioSocketChannel.class)

                     .handler(new MyChatInitlaizer());

             ChannelFuture channelFuture = bootstrap.connect("localhost", 8899).sync();

             Channel channel = channelFuture.channel();

             //channelFuture.channel().writeAndFlush("first msg");//发送数据，其实应该写到handler的active方法中

             BufferedReader br = new BufferedReader(new InputStreamReader( System.in));

             for (;;) {//死循环来接收客户端的输入

                 channel.writeAndFlush(br.readLine() + "\r\n");

             }

 //           channelFuture.channel().closeFuture().sync();

         }finally {

             eventLoopGroup.shutdownGracefully();

         }

     }

 }