服务端启动流程

package com.example.netty;

import com.example.netty.handler.HelloServerHandler;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;

public class HelloServer {

    public static void main(String[] args) {
        NioEventLoopGroup bossGroup = new NioEventLoopGroup();
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();

        ServerBootstrap serverBootstrap = new ServerBootstrap();
        //1. 指定线程组
        serverBootstrap.group(bossGroup, workerGroup)
                .localAddress(8000)//2. 指定端口
                .channel(NioServerSocketChannel.class)//3. 指定IO模型
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel socketChannel) throws Exception {
                        socketChannel.pipeline().addLast(new HelloServerHandler());
                    }
                });//4. 配置业务处理逻辑类
        //5. 绑定端口
        serverBootstrap.bind().addListener((future)->{
            if(future.isSuccess()){
                System.out.println("端口绑定成功");
            }else{
                System.out.println("端口绑定失败:"+future.cause());
            }
        });
    }

}

1. bossGroup和workerGroup可以看作是传统IO网络编程的两个线程组，bossGroup负责 accept 新的socket连接，workerGroup负责socket连接的读写。
2. ServerBootstrap是服务端引导类，负责.group(bossGroup, workerGroup)配置线程模型；.channel指定IO模型，NioServerSocketChannel.class是NIO模型，OioServerSocketChannel.class是传统IO模型；.childHandler配置业务逻辑处理。
3. .bind()绑定端口，该方法是异步执行，所以需要配置监听器。

服务端业务处理类

package com.example.netty.handler;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.CharsetUtil;

public class HelloServerHandler extends ChannelInboundHandlerAdapter {

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf byteBuf = (ByteBuf) msg;
        System.out.println(byteBuf.toString(CharsetUtil.UTF_8));
        ctx.writeAndFlush(Unpooled.copiedBuffer("hello client".getBytes()));
    }
}

主要打印客户端发送的消息并返回Hello Client。

客户端启动流程

package com.example.netty;

import com.example.netty.handler.HelloClientHandler;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;

public class HelloClient {

    public static void main(String[] args) {
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();

        Bootstrap bootstrap = new Bootstrap();
        //1. 配置线程组
        bootstrap.group(workerGroup)
                .channel(NioSocketChannel.class)//2. 指定IO模型
                .remoteAddress("127.0.0.1", 8000)//3. 指定连接ip和端口
                .handler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel socketChannel) throws Exception {
                        socketChannel.pipeline().addLast(new HelloClientHandler());
                    }
                });//4. 配置业务处理逻辑
        //5. 连接
        bootstrap.connect().addListener(future -> {
            if(future.isSuccess()){
                System.out.println("连接成功");
            }else{
                System.out.println("连接失败:" + future.cause());
            }
        });
    }

}

客户端引导类为Bootstrap，而服务端为ServerBootstrap

业务处理逻辑类

package com.example.netty.handler;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.CharsetUtil;

public class HelloClientHandler extends ChannelInboundHandlerAdapter {

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ctx.writeAndFlush(Unpooled.copiedBuffer("hello server".getBytes()));
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf byteBuf = (ByteBuf) msg;
        System.out.println("recieve from server:" + byteBuf.toString(CharsetUtil.UTF_8));
    }
}

主要在连接后向服务端发送Hello Server，并接受打印服务端返回消息。