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。

巴特西

Netty 模型

Demo代码

需要细究的几个点

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