Netty 模型

Demo代码

使用Maven的话请在pom.xml中注入netty依赖

 <!-- https://mvnrepository.com/artifact/io.netty/netty-all -->
    <dependency>
      <groupId>io.netty</groupId>
      <artifactId>netty-all</artifactId>
      <version>4.1.43.Final</version>
    </dependency>

NettyClient

package com.ronnie.netty.sample;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
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 NettyClient {

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

        // 客户端需要一个事件循环组
        NioEventLoopGroup group = new NioEventLoopGroup();

        try {
            // 创建客户端启动对象
            // 注意: 客户端使用的不是 ServerBootstrap 而是 Bootstrap
            Bootstrap bootstrap = new Bootstrap();

            // 设置相关参数
            bootstrap.group(group) //设置线程组
                    .channel(NioSocketChannel.class) // 设置客户端通道实现类(反射)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new NettyClientHandler()); // 加入自己的处理器
                        }
                    });
            System.out.println("Client side is ready......");

            // 启动客户端去连接服务器端
            // channelFuture涉及到netty的异步模型
            ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 6668).sync();

            // 给关闭通道进行监听
            channelFuture.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            group.shutdownGracefully();
        }
    }
}

NettyClientHandler

package com.ronnie.netty.sample;

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 {

    // 当同道就绪, 就会触发该方法
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("Client " + ctx);
        ctx.writeAndFlush(Unpooled.copiedBuffer("Hello, server: ROFL", 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("The message server responded: " + buf.toString(CharsetUtil.UTF_8));
        System.out.println("Server address: " + ctx.channel().remoteAddress());
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

NettyServer

package com.ronnie.netty.sample;

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;

public class NettyServer {
    public static void main(String[] args) throws InterruptedException {

        // 创建 BossGroup 与 WorkerGroup
        /**
         *  1. 创建两个线程组 bossGroup 和 workerGroup
         *  2. bossGroup 只是处理连接请求, 真正的和客户端业务处理, 会交给workGroup完成
         *  3. 两个都是无限循环
         *  4. bossGroup 和 workerGroup 含有的子线程(NioEventLoop)的个数
         *  为默认实际 cpu核数 * 2
         */

        NioEventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            // 创建服务器端的启动对象, 配置参数
            ServerBootstrap bootstrap = new ServerBootstrap();

            // 使用链式编程来进行设置
            bootstrap.group(bossGroup, workerGroup) // 设置两个线程组
                     .channel(NioServerSocketChannel.class) // 使用NioSocketChannel 作为服务器的通道实现
                     .option(ChannelOption.SO_BACKLOG, 128) // 设置线程队列等待连接的个数
                     .childOption(ChannelOption.SO_KEEPALIVE, true) // 设置保持活动连接状态
                     .childHandler(new ChannelInitializer<SocketChannel>() { // 创建一个通道初始化对象(匿名对象)
                         /**
                          *  给pipeline设置处理器
                          * @param ch
                          * @throws Exception
                          */
                         @Override
                         protected void initChannel(SocketChannel ch) throws Exception {
                             ch.pipeline().addLast(new NettyServerHandler());
                         }
                     }); // 给workerGroup的 EventLoop 设置处理器

            System.out.println("Server is ready......");

            // 绑定一个端口并且同步, 生成了一个ChannelFuture对象
            // 启动服务器(并绑定端口)
            ChannelFuture cf = bootstrap.bind(6668).sync();

            // 对关闭通道进行监听
            cf.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            // 优雅地关闭
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }

    }
}

NettyServerHandler

package com.ronnie.netty.sample;

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

/**
 *  1. 自定义一个Handler需要继承 netty 规定好的某个 HandlerAdapter(适配器模式)
 *  2. 这时我们自定义一个Handler, 才能称为一个handler
 */
public class NettyServerHandler extends ChannelInboundHandlerAdapter {

    /**
     *  读取数据事件(这里我们可以读取客户端发送的消息)
     *  ChannelHandlerContext ctx: 上下文对象, 含有管道 pipeline, 通道 channel, 地址 address
     *  Object msg: 就是客户端发送的数据 默认Object
     * @param ctx
     * @param msg
     * @throws Exception
     */
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {

        System.out.println("The server is reading thread: " + Thread.currentThread().getName());
        System.out.println("server ctx = " + ctx);
        System.out.println("Check the relationship between channel and pipeline");
        Channel channel = ctx.channel();
        ChannelPipeline pipeline = ctx.pipeline(); // 本质是一个双向链表, 涉及到出栈入栈问题
        // 将 msg转成一个 ByteBuf(是netty提供的, 不是NIO的 ByteBuffer, 性能更高)
        ByteBuf buf = (ByteBuf) msg;
        System.out.println("The message that client send: " + buf.toString(CharsetUtil.UTF_8));
        System.out.println("The address of client: " + ctx.channel().remoteAddress());
    }

    /**
     *  数据读取完毕
     * @param ctx
     * @throws Exception
     */
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {

        // write + flush, 将数据写入到缓冲并刷新
        // 一般来说, 我们对发送的数据进行编码
        ctx.writeAndFlush(Unpooled.copiedBuffer("Hello, dear client, Kappa", CharsetUtil.UTF_8));

    }

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

需要细究的几个点

bossGroup 和 workerGroup 含有的子线程(NioEventLoop)的个数为默认实际 cpu核数 * 2。

如果传入的为空, 默认传入0

    public NioEventLoopGroup() {
        this(0);
    }

    public NioEventLoopGroup(int nThreads) {
        this(nThreads, (Executor) null);
    }

    public NioEventLoopGroup(int nThreads, Executor executor) {
        this(nThreads, executor, SelectorProvider.provider());
    }

    public NioEventLoopGroup(
            int nThreads, Executor executor, final SelectorProvider selectorProvider) {
        this(nThreads, executor, selectorProvider, DefaultSelectStrategyFactory.INSTANCE);
    }

    public NioEventLoopGroup(int nThreads, Executor executor, final SelectorProvider selectorProvider,
                             final SelectStrategyFactory selectStrategyFactory) {
        super(nThreads, executor, selectorProvider, selectStrategyFactory, RejectedExecutionHandlers.reject());
    }

    /**
     * @see MultithreadEventExecutorGroup#MultithreadEventExecutorGroup(int, Executor, Object...)
     */
    protected MultithreadEventLoopGroup(int nThreads, Executor executor, Object... args) {
        // 如果传入的线程数为0, 就让线程数为默认事件循环线程数, 否则就使用传入的线程数
        super(nThreads == 0 ? DEFAULT_EVENT_LOOP_THREADS : nThreads, executor, args);
    }

一路追踪源码, 最终你会追踪到:

DEFAULT_EVENT_LOOP_THREADS = Math.max(1, SystemPropertyUtil.getInt(
                "io.netty.eventLoopThreads", NettyRuntime.availableProcessors() * 2));

DEFAULT_EVENT_LOOP_THREADS 最小为1, 通常是可获取的cpu核数 * 2

我们可以写个程序测试一下

package com.ronnie.netty.sample;

import io.netty.util.NettyRuntime;

public class Test {
    public static void main(String[] args) {
        System.out.println(NettyRuntime.availableProcessors());
    }
}

打印结果为12, 我的cpu为 i7 8700, 6核12线程, 结论成立。

Pipeline中含有其对应的Channel的属性, Channel中也有其对应的Pipeline的属性, 两者是互相包容的, 而ChannelHandlerContext则包含了此两者, 是个很复杂的接口。

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原文地址：https://www.cnblogs.com/ronnieyuan/p/12016712.html