<dependencies>
        <dependency>
            <groupId>io.netty</groupId>
            <artifactId>netty-all</artifactId>
            <version>4.1.49.Final</version>
        </dependency>

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.68</version>
        </dependency>

    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.6.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

public class MsgBody {


    //发送人名称
    private String sendUserName;


    private String msg;


    public String getSendUserName() {
        return sendUserName;
    }

    public void setSendUserName(String sendUserName) {
        this.sendUserName = sendUserName;
    }


    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }
}

/**
 * netty的服务器
 * @Author: yeyongjian
 * @Date: 2020-05-03 23:34
 */
public class NettyServer {

    private int port;

    public NettyServer(int port) {
        this.port = port;
        bind();
    }

    private void bind() {
        EventLoopGroup boss = new NioEventLoopGroup();
        EventLoopGroup worker = new NioEventLoopGroup();

        try {
            ServerBootstrap bootstrap = new ServerBootstrap();

            bootstrap.group(boss, worker);
            bootstrap.channel(NioServerSocketChannel.class);
            bootstrap.option(ChannelOption.SO_BACKLOG, 1024); // 连接数
            bootstrap.option(ChannelOption.TCP_NODELAY, true); // 不延迟，消息立即发送
            bootstrap.childOption(ChannelOption.SO_KEEPALIVE, true); // 长连接
            bootstrap.childHandler(new ChannelInitializer<SocketChannel>() {
                @Override
                protected void initChannel(SocketChannel socketChannel){
                    ChannelPipeline p = socketChannel.pipeline();
                    ServerHandler serverHandler = new ServerHandler();
                    p.addLast(serverHandler);// 添加NettyServerHandler，用来处理Server端接收和处理消息的逻辑
                }
            });
            ChannelFuture channelFuture = bootstrap.bind(port).sync();
            if (channelFuture.isSuccess()) {
                System.err.println("启动Netty服务成功，端口号：" + this.port);
            }
            // 关闭连接
            channelFuture.channel().closeFuture().sync();

        } catch (Exception e) {
            System.err.println("启动Netty服务异常，异常信息：" + e.getMessage());
            e.printStackTrace();
        } finally {
            boss.shutdownGracefully();
            worker.shutdownGracefully();
        }
    }
    public static void main(String[] args) throws InterruptedException {
        new NettyServer(10086);
    }
}

import com.alibaba.fastjson.JSONObject;
import com.eujian.im.MsgBody;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelId;
import io.netty.channel.SimpleChannelInboundHandler;

import java.io.UnsupportedEncodingException;
import java.util.HashMap;
import java.util.Map;

/**
 * 服务器的处理器
 * @Author: yeyongjian
 * @Date: 2020-05-03 23:35
 */
public class ServerHandler  extends SimpleChannelInboundHandler {

    //连接id与容器的关系
    private static Map<String, ChannelHandlerContext> map = new HashMap<>();


    @Override
    protected void channelRead0(ChannelHandlerContext ctx, Object msg) {
        Channel channel = ctx.channel();
        ChannelId id = channel.id();
        map.put(id.toString(),ctx);
        ByteBuf buf = (ByteBuf) msg;
        String recieved = getMessage(buf);
        MsgBody msgBody = JSONObject.parseObject(recieved, MsgBody.class);
        String format = String.format("服务器接收到客户端消息，发送人：%s，发送信息：%s", msgBody.getSendUserName(), msgBody.getMsg());
        System.err.println(format);

        map.forEach((k,v)->{
            try {
                if(id.toString().equals(k)){
                    return;
                }

                MsgBody sendMsgBody = new MsgBody();
                sendMsgBody.setSendUserName(msgBody.getSendUserName());
                sendMsgBody.setMsg(msgBody.getMsg());
                v.writeAndFlush(getSendByteBuf(JSONObject.toJSONString(sendMsgBody)));