Netty | 属于你的第一款Netty应用程序

<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-all</artifactId>
    <version>4.1.65.Final</version>
</dependency>

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

/**
 * @Author: crush
 * @Date: 2021-08-22 10:19
 * version 1.0
 * @deprecated  @Sharable 表示可以将带注释的ChannelHandler的同一实例多次添加到一个或多个ChannelPipeline ，而不会出现竞争条件。
 */
@ChannelHandler.Sharable
public class EchoServerHandler extends ChannelInboundHandlerAdapter {
    /**
     * 对于每个传入的消息都要调用
     */
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) {
        ByteBuf in = (ByteBuf) msg;
        //将消息记录到控制台
        System.out.println(
                "Server received: " + in.toString(CharsetUtil.UTF_8));
        // 将接收到的消息写给发送者，而不冲刷出站消息
         
        ctx.write(in);
    }

    /**
     * —通知ChannelInboundHandler 最后一次对channelRead()的调用是当前批量读取中的最后一条消息
     */
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) {
       // 将消息发送到远程节点，并且关闭该 Channel
        ctx.writeAndFlush(Unpooled.EMPTY_BUFFER)
                .addListener(ChannelFutureListener.CLOSE);
    }

    /**
     * 在读取操作期间，有异常抛出时会调用
     */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx,
                                Throwable cause) {
        cause.printStackTrace();
        ctx.close();
    }
}

public class EchoServer {
    private final int port;

    public EchoServer(int port) {
        this.port = port;
    }

    public static void main(String[] args) throws Exception {
        int port=8081;
        new EchoServer(port).start();
    }

    public void start() throws Exception {
        final EchoServerHandler serverHandler = new EchoServerHandler();
        //创建EventLoopGroup
        EventLoopGroup bossGroup = new NioEventLoopGroup();

        EventLoopGroup workerGroup = new NioEventLoopGroup(); 
        try {
            //它允许轻松引导ServerChannel
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup,workerGroup)
                    /**用于从中创建Channel实例的Class */
                    .channel(NioServerSocketChannel.class)
                    .localAddress(new InetSocketAddress(port))
                    //添加一个EchoServerHandler 到子Channel的 ChannelPipeline
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        //处理 I/O 事件或拦截 I/O 操作，并将其转发到其ChannelPipeline下一个处理程序
                        @Override
                        public void initChannel(SocketChannel ch)
                                throws Exception {
                              //EchoServerHandler 被标注为@Shareable，所以我们可以总是使用同样的实例
                            ch.pipeline().addLast(serverHandler);
                        }
                    });
            /**
             * 异步地绑定服务器；调用 sync()方法阻塞等待直到绑定完成
             */
            ChannelFuture f = b.bind().sync();
            /**
             * 获取 Channel 的CloseFuture，并且阻塞当前线程直到它完成
             */
            f.channel().closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully().sync();
            workerGroup.shutdownGracefully();
        }
    }
}

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

import java.util.Scanner;

@ChannelHandler.Sharable
public class EchoClientHandler extends SimpleChannelInboundHandler<ByteBuf> {

    /**
     * 在到服务器的连接已经建立之后将被调用；
     */
    @Override
    public void channelActive(ChannelHandlerContext ctx) {
        //当被通知 Channel是活跃的时候，发送一条消息
        ctx.writeAndFlush(Unpooled.copiedBuffer("Netty rocks! 你好丫！！" ,
                CharsetUtil.UTF_8));

    }


    /**
     * 当从服务器接收到一条消息时被调用；
     */
    @Override
    public void channelRead0(ChannelHandlerContext ctx, ByteBuf in) {
        // 记录已接收消息的转储
        System.out.println(
                "Client received: " + in.toString(CharsetUtil.UTF_8));
    }

    /**
     * 在处理过程中引发异常时被调用。
     */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx,
                                Throwable cause) {
        cause.printStackTrace();
        ctx.close();
    }
}

import io.netty.bootstrap.Bootstrap;
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 java.net.InetSocketAddress;

public class EchoClient {
    private final String host;
    private final int port;

    public EchoClient(String host, int port) {
        this.host = host;
        this.port = port;
    }

    public void start() throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            //指定 EventLoopGroup 以处理客户端事件；需要适用于 NIO 的实现
            b.group(group)
                    .channel(NioSocketChannel.class)
                    .remoteAddress(new InetSocketAddress(host, port))
                    //在创建Channel时，向 ChannelPipeline中添加一个 EchoClientHandler 实例
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch)
                                throws Exception {
                            ch.pipeline().addLast(
                                    new EchoClientHandler());
                        }
                    });
            ChannelFuture f = b.connect().sync();
            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
    }

    public static void main(String[] args) throws Exception {
        String host="localhost";
        int port=8081;
        new EchoClient(host, port).start();
    }
}