Netty是Trustin Lee在2004年开发的一款高性能的网络应用程序框架。相比于JDK自带的NIO，Netty做了相当多的增强，且隔离了jdk nio的实现细节，API也比较友好，还支持流量整形等高级特性。在我们常见的一些开源项目中已经普遍的应用到了Netty，比如Dubbo、Elasticsearch、Zookeeper等。

Netty的具体开发

提示：因代码相对较多，这里只展示其主要部分，至于项目中用到的编解码器、工具类，请直接拉到最后下载源码！也欢迎顺手给个Star～

需要的依赖

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
</dependency>

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
</dependency>
<dependency>
    <groupId>io.dropwizard.metrics</groupId>
    <artifactId>metrics-core</artifactId>
    <version>4.1.1</version>
</dependency>
<dependency>
    <groupId>io.dropwizard.metrics</groupId>
    <artifactId>metrics-jmx</artifactId>
    <version>4.1.1</version>
</dependency>
<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
</dependency>
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-all</artifactId>
    <version>4.1.29.Final</version>
</dependency>

Client端代码

package com.example.nettydemo.client;

import com.example.nettydemo.client.codec.*;
import com.example.nettydemo.client.codec.dispatcher.OperationResultFuture;
import com.example.nettydemo.client.codec.dispatcher.RequestPendingCenter;
import com.example.nettydemo.client.codec.dispatcher.ResponseDispatcherHandler;
import com.example.nettydemo.common.RequestMessage;
import com.example.nettydemo.common.string.StringOperation;
import com.example.nettydemo.util.IdUtil;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioChannelOption;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;

import javax.net.ssl.SSLException;
import java.util.concurrent.ExecutionException;

public class Client {

    public static void main(String[] args) throws InterruptedException, ExecutionException, SSLException {

        Bootstrap bootstrap = new Bootstrap();
        bootstrap.channel(NioSocketChannel.class);

        //客户端连接服务器最大允许时间，默认为30s
        bootstrap.option(NioChannelOption.CONNECT_TIMEOUT_MILLIS, 30 * 1000); //10s

        NioEventLoopGroup group = new NioEventLoopGroup();
        try {

            bootstrap.group(group);

            RequestPendingCenter requestPendingCenter = new RequestPendingCenter();
            LoggingHandler loggingHandler = new LoggingHandler(LogLevel.INFO);

            bootstrap.handler(new ChannelInitializer<NioSocketChannel>() {
                @Override
                protected void initChannel(NioSocketChannel ch) throws Exception {
                    ChannelPipeline pipeline = ch.pipeline();

                    pipeline.addLast(new FrameDecoder());
                    pipeline.addLast(new FrameEncoder());

                    pipeline.addLast(new ProtocolEncoder());
                    pipeline.addLast(new ProtocolDecoder());

                    pipeline.addLast(new ResponseDispatcherHandler(requestPendingCenter));
                    pipeline.addLast(new OperationToRequestMessageEncoder());

//                    pipeline.addLast(loggingHandler);

                }
            });

            //连接服务
            ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 8888);
            //因为future是异步执行，所以需要先连接上后，再进行下一步操作
            channelFuture.sync();

            long streamId = IdUtil.nextId();
            /**
             * 发送数据测试，按照定义的规则组装数据
             */
//            OrderOperation orderOperation =  new OrderOperation(1001, "你好啊，hi");
            RequestMessage requestMessage = new RequestMessage(streamId, new StringOperation(1234, "你好啊，hi"));

            //将future放入center
            OperationResultFuture operationResultFuture = new OperationResultFuture();
            requestPendingCenter.add(streamId, operationResultFuture);

            //发送消息
            for (int i = 0; i < 10; i++) {
                channelFuture.channel().writeAndFlush(requestMessage);
            }

            //阻塞等待结果,结果来了之后会调用ResponseDispatcherHandler去set结果
//            OperationResult operationResult = operationResultFuture.get();
//            //将结果打印
//            System.out.println("返回:"+operationResult);

            channelFuture.channel().closeFuture().get();

        } finally {
            group.shutdownGracefully();
        }

    }

}

Server端代码

package com.example.nettydemo.server;

import com.example.nettydemo.server.codec.FrameDecoder;
import com.example.nettydemo.server.codec.FrameEncoder;
import com.example.nettydemo.server.codec.ProtocolDecoder;
import com.example.nettydemo.server.codec.ProtocolEncoder;
import com.example.nettydemo.server.handler.MetricsHandler;
import com.example.nettydemo.server.handler.ServerIdleCheckHandler;
import com.example.nettydemo.server.handler.ServerProcessHandler;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioChannelOption;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.flush.FlushConsolidationHandler;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import io.netty.handler.traffic.GlobalTrafficShapingHandler;
import io.netty.util.concurrent.DefaultThreadFactory;
import io.netty.util.concurrent.UnorderedThreadPoolEventExecutor;
import lombok.extern.slf4j.Slf4j;

import javax.net.ssl.SSLException;
import java.security.cert.CertificateException;
import java.util.concurrent.ExecutionException;

/**
 * netty server 入口
 */
@Slf4j
public class Server {

    public static void main(String... args) throws InterruptedException, ExecutionException, CertificateException, SSLException {

        ServerBootstrap serverBootstrap = new ServerBootstrap();
        //设置channel模式，因为是server所以使用NioServerSocketChannel
        serverBootstrap.channel(NioServerSocketChannel.class);

        //最大的等待连接数量
        serverBootstrap.option(NioChannelOption.SO_BACKLOG, 1024);
        //设置是否启用 Nagle 算法:用将小的碎片数据连接成更大的报文 来提高发送效率。
        //如果需要发送一些较小的报文，则需要禁用该算法
        serverBootstrap.childOption(NioChannelOption.TCP_NODELAY, true);

        //设置netty自带的log，并设置级别
        serverBootstrap.handler(new LoggingHandler(LogLevel.INFO));

        //thread
        //用户指定线程名
        NioEventLoopGroup bossGroup = new NioEventLoopGroup(0, new DefaultThreadFactory("boss"));
        NioEventLoopGroup workGroup = new NioEventLoopGroup(0, new DefaultThreadFactory("worker"));
        UnorderedThreadPoolEventExecutor businessGroup = new UnorderedThreadPoolEventExecutor(10, new DefaultThreadFactory("business"));

        //只能使用一个线程，因GlobalTrafficShapingHandler比较轻量级
        NioEventLoopGroup eventLoopGroupForTrafficShaping = new NioEventLoopGroup(0, new DefaultThreadFactory("TS"));

        try {
            //设置react方式
            serverBootstrap.group(bossGroup, workGroup);

            //metrics
            MetricsHandler metricsHandler = new MetricsHandler();

            //trafficShaping流量整形
            //long writeLimit 写入时控制, long readLimit 读取时控制 具体设置看业务修改
            GlobalTrafficShapingHandler globalTrafficShapingHandler = new GlobalTrafficShapingHandler(eventLoopGroupForTrafficShaping, 10 * 1024 * 1024, 10 * 1024 * 1024);

            //log
            LoggingHandler debugLogHandler = new LoggingHandler(LogLevel.DEBUG);
            LoggingHandler infoLogHandler = new LoggingHandler(LogLevel.INFO);

            //设置childHandler，按执行顺序放
            serverBootstrap.childHandler(new ChannelInitializer<NioSocketChannel>() {
                @Override
                protected void initChannel(NioSocketChannel ch) throws Exception {

                    ChannelPipeline pipeline = ch.pipeline();

                    pipeline.addLast("debugLog", debugLogHandler);
                    pipeline.addLast("tsHandler", globalTrafficShapingHandler);
                    pipeline.addLast("metricHandler", metricsHandler);
                    pipeline.addLast("idleHandler", new ServerIdleCheckHandler());

                    pipeline.addLast("frameDecoder", new FrameDecoder());
                    pipeline.addLast("frameEncoder", new FrameEncoder());
                    pipeline.addLast("protocolDecoder", new ProtocolDecoder());
                    pipeline.addLast("protocolEncoder", new ProtocolEncoder());

                    pipeline.addLast("infoLog", infoLogHandler);
                    //对flush增强，减少flush次数牺牲延迟增强吞吐量
                    pipeline.addLast("flushEnhance", new FlushConsolidationHandler(10, true));
                    //为业务处理指定单独的线程池
                    pipeline.addLast(businessGroup, new ServerProcessHandler());//businessGroup,
                }
            });

            //绑定端口并阻塞启动
            ChannelFuture channelFuture = serverBootstrap.bind(8888).sync();

            channelFuture.channel().closeFuture().sync();

        } finally {
            bossGroup.shutdownGracefully();
            workGroup.shutdownGracefully();
            businessGroup.shutdownGracefully();
            eventLoopGroupForTrafficShaping.shutdownGracefully();
        }

    }

}

最后

以上介绍了Netty的基本用法，在代码中也做了一部分的关键注释，但可能还会有许多不足，也不可能满足所有人的要求，大家可根据自己的实际需求去改造此项目。附上源码地址netty源码

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