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

1. 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。

2. 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。