Netty简单案例

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Netty是一个异步事件驱动的网络应用框架，用于快速开发可维护的高性能服务器和客户端。

• 引入Maven依赖

<!-- https://mvnrepository.com/artifact/io.netty/netty-all -->
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-all</artifactId>
    <version>4.1.34.Final</version>
</dependency>

• 服务器端

package com.example.demo.netty;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.string.StringDecoder;

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

        serverBootstrap.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).childHandler(new ChannelInitializer<NioSocketChannel>() {
            @Override
            protected void initChannel(NioSocketChannel nioSocketChannel) {
                nioSocketChannel.pipeline().addLast(new StringDecoder());

                nioSocketChannel.pipeline().addLast(new SimpleChannelInboundHandler<String>() {
                    @Override
                    protected void channelRead0(ChannelHandlerContext channelHandlerContext, String message) {
                        System.out.println(message);
                    }
                });
            }
        }).bind(8000);
    }
}

• 客户端

package com.example.demo.netty;

import java.util.Date;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.string.StringEncoder;

public class NettyClient {
    public static void main(String[] args) throws InterruptedException {
        Bootstrap bootstrap = new Bootstrap();
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();

        Channel channel = bootstrap.group(workerGroup).channel(NioSocketChannel.class).handler(new ChannelInitializer<NioSocketChannel>() {
            @Override
            protected void initChannel(NioSocketChannel nioSocketChannel) {
                nioSocketChannel.pipeline().addLast(new StringEncoder());
            }
        }).connect("127.0.0.1", 8000).sync().channel();

        while (true) {
            channel.writeAndFlush(new Date() + ": hello world!");
            Thread.sleep(2000);
        }
    }
}

• 案例：自动绑定递增端口

package com.example.demo.netty;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.util.concurrent.Future;
import io.netty.util.concurrent.GenericFutureListener;

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

        serverBootstrap.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).childHandler(new ChannelInitializer<NioSocketChannel>() {
            @Override
            protected void initChannel(NioSocketChannel nioSocketChannel) {
                nioSocketChannel.pipeline().addLast(new StringDecoder());

                nioSocketChannel.pipeline().addLast(new SimpleChannelInboundHandler<String>() {
                    @Override
                    protected void channelRead0(ChannelHandlerContext channelHandlerContext, String message) {
                        System.out.println(message);
                    }
                });
            }
        });

        bind(serverBootstrap, 8000);
    }

    public static void bind(ServerBootstrap serverBootstrap, int port) {
        serverBootstrap.bind(port).addListener(new GenericFutureListener<Future<? super Void>>() {
            @Override
            public void operationComplete(Future<? super Void> future) throws Exception {
                if (future.isSuccess()) {
                    System.out.println("端口[" + port + "]绑定成功!");
                } else {
                    System.err.println("端口[" + port + "]绑定失败!");
                    bind(serverBootstrap, port + 1);
                }
            }
        });
    }
}

• 案例：失败重连

package com.example.demo.netty;

import java.util.Date;
import java.util.concurrent.TimeUnit;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;

public class Test {
    public static final int MAX_RETRY = 5;

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

        bootstrap.group(workerGroup).channel(NioSocketChannel.class).handler(new ChannelInitializer<NioSocketChannel>() {
            @Override
            protected void initChannel(NioSocketChannel nioSocketChannel) throws Exception {}
        });

        connect(bootstrap, "127.0.0.1", 8000, MAX_RETRY);
    }

    public static void connect(Bootstrap bootstrap, String host, int port, int retry) {
        bootstrap.connect(host, port).addListener(future -> {
            if (future.isSuccess()) {
                System.out.println("连接成功");
            } else if (retry == 0) {
                System.err.println("重试次数已用完，放弃连接！");
            } else {
                int order = (MAX_RETRY - retry) + 1;
                int delay = 1 << order;
                System.err.println(new Date() + ": 连接失败，第" + order + "次重连……");
                bootstrap.config().group().schedule(() -> connect(bootstrap, host, port, retry - 1), delay, TimeUnit.SECONDS);
            }
        });
    }
}

• 案例：客户端与服务器端双向通信
• • 服务器端

package com.example.demo.netty;

import java.nio.charset.Charset;
import java.util.Date;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;

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

        serverBootstrap.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).childHandler(new ChannelInitializer<NioSocketChannel>() {
            @Override
            protected void initChannel(NioSocketChannel nioSocketChannel) {
                nioSocketChannel.pipeline().addLast(new FirstServerHandler());
            }
        }).bind(8000);
    }
}

class FirstServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext channelHandlerContext, Object message) throws Exception {
        ByteBuf byteBufIn = (ByteBuf) message;
        System.out.println(new Date() + ": 服务端读到数据 -> " + byteBufIn.toString(Charset.forName("utf-8")));

        // 回复数据到客户端
        System.out.println(new Date() + ": 服务端写出数据");
        ByteBuf byteBufOut = getByteBuf(channelHandlerContext);
        channelHandlerContext.channel().writeAndFlush(byteBufOut);
    }

    private ByteBuf getByteBuf(ChannelHandlerContext channelHandlerContext) {
        byte[] bs = "Hello World".getBytes(Charset.forName("utf-8"));
        ByteBuf byteBuf = channelHandlerContext.alloc().buffer();
        byteBuf.writeBytes(bs);
        return byteBuf;
    }
}

• • 客户端

package com.example.demo.netty;

import java.nio.charset.Charset;
import java.util.Date;

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;

public class NettyClient {
    public static void main(String[] args) throws InterruptedException {
        Bootstrap bootstrap = new Bootstrap();
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();

        bootstrap.group(workerGroup).channel(NioSocketChannel.class).handler(new ChannelInitializer<NioSocketChannel>() {
            @Override
            protected void initChannel(NioSocketChannel nioSocketChannel) {
                nioSocketChannel.pipeline().addLast(new FirstClientHandler());
            }
        }).connect("127.0.0.1", 8000);
    }
}

class FirstClientHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelActive(ChannelHandlerContext channelHandlerContext) throws Exception {
        System.out.println(new Date() + ": 客户端写出数据");
        ByteBuf buffer = getByteBuf(channelHandlerContext);
        channelHandlerContext.channel().writeAndFlush(buffer);
    }

    private ByteBuf getByteBuf(ChannelHandlerContext channelHandlerContext) {
        ByteBuf byteBuf = channelHandlerContext.alloc().buffer();
        byte[] bs = "Hello Leif".getBytes(Charset.forName("utf-8"));
        byteBuf.writeBytes(bs);
        return byteBuf;
    }

    @Override
    public void channelRead(ChannelHandlerContext channelHandlerContext, Object message) throws Exception {
        ByteBuf byteBuf = (ByteBuf) message;
        System.out.println(new Date() + ": 客户端读到数据 -> " + byteBuf.toString(Charset.forName("utf-8")));
    }
}

• ByteBuf API

package com.example.demo.netty;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;

public class ByteBufTest {
    public static void main(String[] args) {
        ByteBuf byteBuf = ByteBufAllocator.DEFAULT.buffer(9, 100);
        print("allocate ByteBuf(9, 100)", byteBuf);

        // write方法改变写指针，写完之后写指针未到capacity的时候，buffer仍然可写
        byteBuf.writeBytes(new byte[] {1, 2, 3, 4});
        print("writeBytes(1,2,3,4)", byteBuf);

        // write方法改变写指针，写完之后写指针未到capacity的时候，buffer仍然可写, 写完int类型之后，写指针增加4
        byteBuf.writeInt(12);
        print("writeInt(12)", byteBuf);

        // write方法改变写指针, 写完之后写指针等于capacity的时候，buffer不可写
        byteBuf.writeBytes(new byte[] {5});
        print("writeBytes(5)", byteBuf);

        // write方法改变写指针，写的时候发现buffer不可写则开始扩容，扩容之后capacity随即改变
        byteBuf.writeBytes(new byte[] {6});
        print("writeBytes(6)", byteBuf);

        // get方法不改变读写指针
        System.out.println("getByte(3) return: " + byteBuf.getByte(3));
        System.out.println("getShort(3) return: " + byteBuf.getShort(3));
        System.out.println("getInt(3) return: " + byteBuf.getInt(3));
        print("getByte()", byteBuf);

        // set方法不改变读写指针
        byteBuf.setByte(byteBuf.readableBytes() + 1, 0);
        print("setByte()", byteBuf);

        // read方法改变读指针
        byte[] dst = new byte[byteBuf.readableBytes()];
        byteBuf.readBytes(dst);
        print("readBytes(" + dst.length + ")", byteBuf);
    }

    private static void print(String action, ByteBuf buffer) {
        System.out.println("after ==========" + action + "==========");
        System.out.println("capacity(): " + buffer.capacity());
        System.out.println("maxCapacity(): " + buffer.maxCapacity());
        System.out.println("readerIndex(): " + buffer.readerIndex());
        System.out.println("readableBytes(): " + buffer.readableBytes());
        System.out.println("isReadable(): " + buffer.isReadable());
        System.out.println("writerIndex(): " + buffer.writerIndex());
        System.out.println("writableBytes(): " + buffer.writableBytes());
        System.out.println("isWritable(): " + buffer.isWritable());
        System.out.println("maxWritableBytes(): " + buffer.maxWritableBytes());
        System.out.println();
    }
}

after ==========allocate ByteBuf(9, 100)==========
capacity(): 9
maxCapacity(): 100
readerIndex(): 0
readableBytes(): 0
isReadable(): false
writerIndex(): 0
writableBytes(): 9
isWritable(): true
maxWritableBytes(): 100

after ==========writeBytes(1,2,3,4)==========
capacity(): 9
maxCapacity(): 100
readerIndex(): 0
readableBytes(): 4
isReadable(): true
writerIndex(): 4
writableBytes(): 5
isWritable(): true
maxWritableBytes(): 96

after ==========writeInt(12)==========
capacity(): 9
maxCapacity(): 100
readerIndex(): 0
readableBytes(): 8
isReadable(): true
writerIndex(): 8
writableBytes(): 1
isWritable(): true
maxWritableBytes(): 92

after ==========writeBytes(5)==========
capacity(): 9
maxCapacity(): 100
readerIndex(): 0
readableBytes(): 9
isReadable(): true
writerIndex(): 9
writableBytes(): 0
isWritable(): false
maxWritableBytes(): 91

after ==========writeBytes(6)==========
capacity(): 64
maxCapacity(): 100
readerIndex(): 0
readableBytes(): 10
isReadable(): true
writerIndex(): 10
writableBytes(): 54
isWritable(): true
maxWritableBytes(): 90

getByte(3) return: 4
getShort(3) return: 1024
getInt(3) return: 67108864
after ==========getByte()==========
capacity(): 64
maxCapacity(): 100
readerIndex(): 0
readableBytes(): 10
isReadable(): true
writerIndex(): 10
writableBytes(): 54
isWritable(): true
maxWritableBytes(): 90

after ==========setByte()==========
capacity(): 64
maxCapacity(): 100
readerIndex(): 0
readableBytes(): 10
isReadable(): true
writerIndex(): 10
writableBytes(): 54
isWritable(): true
maxWritableBytes(): 90

after ==========readBytes(10)==========
capacity(): 64
maxCapacity(): 100
readerIndex(): 10
readableBytes(): 0
isReadable(): false
writerIndex(): 10
writableBytes(): 54
isWritable(): true
maxWritableBytes(): 90