步骤1：创建server

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.FixedLengthFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
public class Server {
	public static void main(String[] args) throws Exception{
		//1创建2个线程，一个是负责接收客户端的连接。一个是负责进行数据传输的
		EventLoopGroup pGroup = new NioEventLoopGroup(1);
		EventLoopGroup cGroup = new NioEventLoopGroup();
		 //2 创建服务器辅助类
		 ServerBootstrap b = new ServerBootstrap();
		 b.group(pGroup, cGroup)
		 .channel(NioServerSocketChannel.class)
		 .option(ChannelOption.SO_BACKLOG, 1024)
		 .option(ChannelOption.SO_SNDBUF, 32*1024)
		 .option(ChannelOption.SO_RCVBUF, 32*1024)
		 .childHandler(new ChannelInitializer<SocketChannel>() {
			@Override
			protected void initChannel(SocketChannel sc) throws Exception {
				//设置定长字符串接收
				sc.pipeline().addLast(new FixedLengthFrameDecoder(5));
				//设置字符串形式的解码
				sc.pipeline().addLast(new StringDecoder());
				sc.pipeline().addLast(new ServerHandler());
		 	}
		 });
		//4 绑定连接
		ChannelFuture cf = b.bind(8765).sync();
		//等待服务器监听端口关闭
		cf.channel().closeFuture().sync();
		pGroup.shutdownGracefully();
		cGroup.shutdownGracefully();
	}
}

步骤2：创建server对应Handler处理

import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import java.net.InetSocketAddress;

public class ServerHandler extends ChannelInboundHandlerAdapter {
	@Override
	public void channelActive(ChannelHandlerContext ctx) throws Exception {
		//上线处理
		InetSocketAddress ipSocket = (InetSocketAddress)ctx.channel().remoteAddress();
		String clientIp = ipSocket.getAddress().getHostAddress();
		String lo =  ctx.channel().remoteAddress().toString();
		System.out.println("客户端ip地址："+clientIp+"上线");
		System.out.println("客户端ip地址："+lo+"上线");
	}
	@Override
	public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
	    //接受客户端数据并进行业务处理
		String request = (String)msg;
		System.out.println("Server :" + msg);
		String response =  request ;
		ctx.writeAndFlush(Unpooled.copiedBuffer(response.getBytes()));
	}
	@Override
	public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
		//断开链接处理和数据完成处理
		System.out.println("断开链接处理 ");
	}
	@Override
	public void exceptionCaught(ChannelHandlerContext ctx, Throwable t) throws Exception {
		//异常处理
		System.out.println(" server 111 ");
	}
}

步骤3：创建client

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.FixedLengthFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
public class Client {
	public static void main(String[] args) throws Exception {
	    //步骤1：
		EventLoopGroup group = new NioEventLoopGroup();
		//步骤2：
		Bootstrap b = new Bootstrap();
		b.group(group)
		 .channel(NioSocketChannel.class)
		 .handler(new ChannelInitializer<SocketChannel>() {
			@Override
			protected void initChannel(SocketChannel sc) throws Exception {
				sc.pipeline().addLast(new FixedLengthFrameDecoder(5));
				sc.pipeline().addLast(new StringDecoder());
				sc.pipeline().addLast(new ClientHandler());
			}
		});
		//步骤3：
		ChannelFuture cf = b.connect("127.0.0.1", 8765).sync();
		cf.channel().writeAndFlush(Unpooled.wrappedBuffer("aaaaabbbbb".getBytes()));
		Thread.sleep(2000);
		cf.channel().writeAndFlush(Unpooled.copiedBuffer("ccccccc".getBytes()));
		
		//步骤4: 等待客户端端口关闭
		cf.channel().closeFuture().sync();
		group.shutdownGracefully();
	}
}

步骤4：创建client对应的handler业务处理

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
public class ClientHandler extends ChannelInboundHandlerAdapter{
	@Override
	public void channelActive(ChannelHandlerContext ctx) throws Exception {
		System.out.println("client channel active... ");
	}
	@Override
	public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
		String response = (String)msg;
		System.out.println("Client: " + response);
	}
	@Override
	public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
		System.out.println("111");
	}
	@Override
	public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
		System.out.println("000");
	}
}

图片运行案例：