【Java】Netty创建网络服务端客户端（TCP/UDP）

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这篇文章主要介绍Netty创建网络服务端客户端示例。
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1. Netty介绍

Netty官网：https://netty.io/

Netty是一个基于Java的异步事件驱动的网络应用程序框架，专门用于快速开发高性能、可扩展和可维护的网络服务器和客户端。它提供了简单而强大的API，使开发人员能够轻松地构建各种网络应用，包括TCP、UDP、HTTP、WebSocket等。

以下是一些关键特点和功能：

1.异步和事件驱动：Netty使用非阻塞I/O模型，通过异步事件驱动方式处理网络操作，提供了卓越的性能和可扩展性。

2.高性能：Netty通过有效地利用底层操作系统提供的机制（如选择器、零拷贝等）来实现高效的数据传输和处理，以满足对性能和吞吐量的要求。

3.安全：Netty提供了强大的加密和认证支持，包括SSL/TLS和各种认证机制，保护网络通信的安全性。

4.多协议支持：Netty支持多种主流的网络协议，如TCP、UDP、HTTP、WebSocket等，使开发人员可以方便地构建不同类型的网络应用。

5.灵活的处理程序模型：Netty采用了高度可扩展的处理程序（Handler）模型，使开发人员可以按需配置和组合处理程序来处理网络事件和数据，实现复杂的业务逻辑。

6.内置编解码器：Netty提供了丰富的内置编解码器，使开发人员能够轻松地处理各种协议和数据格式，简化了网络通信中的数据编解码工作。

7.完善的文档和社区支持：Netty拥有完善的官方文档、示例代码和教程，以及活跃的社区支持，使开发人员能够快速上手并解决问题。

2. 环境安装与配置

IDEA创建Netty工程，只要在pom.xml中引入如下依赖：

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

3. TCP应用示例

创建TCP服务端客户端，需要先开启通道Channel，然后再有一个事件处理Handler，下面就创建这4个类：

NettyServer.java

package org.example;

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.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;

public class NettyServer {
    private final int port;

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

    public void start() throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 128)
                    .handler(new LoggingHandler(LogLevel.INFO))
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new NettyServerHandler()); // channel to handler
                        }
                    });

            ChannelFuture f = b.bind(port).sync();
            System.out.println("Server started on port " + port);

            f.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
            bossGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port = 8080;
        NettyServer server = new NettyServer(port);
        server.start();
    }
}

NettyServerHandler.java

package org.example;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.*;
import io.netty.util.CharsetUtil;

public class NettyServerHandler extends ChannelInboundHandlerAdapter {
    /**
     * 读取数据实际(这里我们可以读取客户端发送的消息)
     * @param ctx 上下文对象
     * @param msg 客户端发送的数据
     * @throws Exception
     */
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        System.out.println("server ctx =" + ctx);
        Channel channel = ctx.channel();
        // 将 msg 转成一个 ByteBuf
        // ByteBuf 是 Netty 提供的，不是 NIO 的 ByteBuffer.
        ByteBuf buf = (ByteBuf) msg;
        System.out.println("客户端发送的消息是: " + buf.toString(CharsetUtil.UTF_8));
        System.out.println("客户端地址: " + channel.remoteAddress());
    }

    /**
     * 读取完毕，回复
     * @param ctx
     * @throws Exception
     */
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        // writeAndFlush 是 write + flush 将数据写入到缓存，并刷新
        ctx.writeAndFlush(Unpooled.copiedBuffer("Hello, Client!", CharsetUtil.UTF_8));
    }

    /**
     * 处理异常, 一般是需要关闭通道
     * @param ctx
     * @param cause
     * @throws Exception
     */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        ctx.close();
    }
}

NettyClient.java

package org.example;

import io.netty.bootstrap.Bootstrap;
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.NioSocketChannel;

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

    public NettyClient(String host, int port) {
        this.host = host; // ip
        this.port = port; // port
    }

    public void start() throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();

        try {
            Bootstrap b = new Bootstrap();
            b.group(group)
                    .channel(NioSocketChannel.class)
                    .option(ChannelOption.TCP_NODELAY, true)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new NettyClientHandler());
                        }
                    });

            ChannelFuture f = b.connect(host, port).sync();
            System.out.println("Connected to " + host + ":" + port);

            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        String host = "localhost";
        int port = 8080;
        NettyClient client = new NettyClient(host, port);
        client.start();
    }
}

NettyClientHandler.java

package org.example;

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 NettyClientHandler extends ChannelInboundHandlerAdapter {
    /**
     * 通道创建就绪后触发
     * @param ctx
     * @throws Exception
     */
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("client ctx =" + ctx);
        ctx.writeAndFlush(Unpooled.copiedBuffer("Hello, Server!", CharsetUtil.UTF_8));
    }

    /**
     * 当通道有读取事件时，会触发
     * @param ctx
     * @param msg
     * @throws Exception
     */
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf buf = (ByteBuf) msg;
        System.out.println("服务器回复的消息:" + buf.toString(CharsetUtil.UTF_8));
        System.out.println("服务器的地址： "+ ctx.channel().remoteAddress());
    }

    /**
     * 处理异常, 一般是需要关闭通道
     * @param ctx
     * @param cause
     * @throws Exception
     */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

分别运行服务端和客户端类，结果如下：

4. UDP应用示例

跟上面TCP类似，UDP也是要创建Channel和Handler，下面创建这4个类：

UDPServer.java

package org.example;

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.DatagramChannel;
import io.netty.channel.socket.nio.NioDatagramChannel;

public class UDPServer {
    private final int port;

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

    public void start() throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();

        try {
            Bootstrap b = new Bootstrap();
            b.group(group)
                    .channel(NioDatagramChannel.class)
                    .handler(new ChannelInitializer<DatagramChannel>() {
                        @Override
                        protected void initChannel(DatagramChannel ch) throws Exception {
                            ch.pipeline().addLast(new UDPServerHandler());
                        }
                    });

            ChannelFuture f = b.bind(port).sync();
            System.out.println("Server started on port " + port);
            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port = 8888;
        UDPServer server = new UDPServer(port);
        server.start();
    }
}

UDPServerHandler.java

package org.example;

import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.socket.DatagramPacket;
import io.netty.util.CharsetUtil;

public class UDPServerHandler extends SimpleChannelInboundHandler<DatagramPacket> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, DatagramPacket msg) throws Exception {
        // 处理接收到的数据
        String receivedMessage = msg.content().toString(CharsetUtil.UTF_8);
        System.out.println("Received message: " + receivedMessage);

        // 响应客户端
        String responseMessage = "Hello, client!";
        DatagramPacket responsePacket = new DatagramPacket(Unpooled.copiedBuffer(responseMessage, CharsetUtil.UTF_8),
                msg.sender());
        ctx.writeAndFlush(responsePacket);
    }
}

UDPClient.java

package org.example;

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.DatagramChannel;
import io.netty.channel.socket.DatagramPacket;
import io.netty.channel.socket.nio.NioDatagramChannel;
import io.netty.util.CharsetUtil;

import java.net.InetSocketAddress;

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

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

    public void start() throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();

        try {
            Bootstrap b = new Bootstrap();
            b.group(group)
                    .channel(NioDatagramChannel.class)
                    .handler(new ChannelInitializer<DatagramChannel>() {
                        @Override
                        protected void initChannel(DatagramChannel ch) throws Exception {
                            ch.pipeline().addLast(new UDPClientHandler());
                        }
                    });

            ChannelFuture f = b.bind(0).sync();
            System.out.println("Client started");

            // 发送消息给服务端
            String message = "Hello, server!";
            DatagramPacket packet = new DatagramPacket(Unpooled.copiedBuffer(message, CharsetUtil.UTF_8),
                    new InetSocketAddress(host, port));
            f.channel().writeAndFlush(packet).sync();

            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        String host = "localhost";
        int port = 8888;
        UDPClient client = new UDPClient(host, port);
        client.start();
    }
}

UDPClientHandler.java

package org.example;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.socket.DatagramPacket;
import io.netty.util.CharsetUtil;

public class UDPClientHandler extends SimpleChannelInboundHandler<DatagramPacket> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, DatagramPacket msg) throws Exception {
        // 处理接收到的数据
        String receivedMessage = msg.content().toString(CharsetUtil.UTF_8);
        System.out.println("Received response from server: " + receivedMessage);
    }
}

运行结果如下：

以上。