Netty源码剖析

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在官网 (netty.io) 下载 netty-4.1.69.final 最新版源码，使用 IDEA 打开，并找到 Example 模块其中的 echo 文件夹下的 EchoServer 代码，启动编译。通常，会有报错产生，缺少 io.netty.util.collection.* 的相关类，本质上是缺乏通过 groovy 脚本自动生成的类导致编译失败，可以通过如下方式解决：

在 IDEA terminal 控制台中键入并运行如下命令即可成功编译

cd common mvn clean compile -Dcheckstyle.skip=true 因为 Netty 源码繁杂，刚开始阅读难以理清思路，所以以 Netty 主线启动的方式展开。以 Netty Source Code 源码中 Example 模块的 EchoServer 服务端和 EchoClient 客户端示例程序为例，展开描述。

服务端 EchoServer

public final class EchoServer {

    static final boolean SSL = System.getProperty("ssl") != null;
    static final int PORT = Integer.parseInt(System.getProperty("port", "8007"));

    public static void main(String[] args) throws Exception {
        // 加密相关
        // Configure SSL.
        final SslContext sslCtx;
        if (SSL) {
            SelfSignedCertificate ssc = new SelfSignedCertificate();
            sslCtx = SslContextBuilder.forServer(ssc.certificate(), ssc.privateKey()).build();
        } else {
            sslCtx = null;
        }

        // Configure the server.
        // 创建两个线程组(类似线程池)，bossGroup主要用于创建线程接收连接请求，设置NioEventLoop数量为1
        // workGroup主要用于创建线程处理IO操作，未设置值，默认线程数为cpu核心数的2倍
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        // 创建服务器处理类
        final EchoServerHandler serverHandler = new EchoServerHandler();
        try {
            // 创建服务器类
            ServerBootstrap b = new ServerBootstrap();
            // 责任链设计模式
            b.group(bossGroup, workerGroup) //配置线程组
             .channel(NioServerSocketChannel.class)  //配置通道方式，可以设置NIO或BIO
             .option(ChannelOption.SO_BACKLOG, 100)  //配置通道选项
             .handler(new LoggingHandler(LogLevel.INFO))  //配置日志服务类
             .childHandler(new ChannelInitializer<SocketChannel>() {
                 @Override
                 public void initChannel(SocketChannel ch) throws Exception {  //配置pipeline
                     ChannelPipeline p = ch.pipeline();
                     if (sslCtx != null) {
                         p.addLast(sslCtx.newHandler(ch.alloc()));
                     }
                     //p.addLast(new LoggingHandler(LogLevel.INFO));
                     p.addLast(serverHandler);
                 }
             });

            // Start the server.
            ChannelFuture f = b.bind(PORT).sync();

            // Wait until the server socket is closed.
            f.channel().closeFuture().sync();
        } finally {
            // Shut down all event loops to terminate all threads.
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

服务处理类 EchoServerHandler

@Sharable
public class EchoServerHandler extends ChannelInboundHandlerAdapter {

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) {
        ctx.write(msg);
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) {
        ctx.flush();
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        // Close the connection when an exception is raised.
        cause.printStackTrace();
        ctx.close();
    }
}

客户端 EchoClient

public final class EchoClient {

    static final boolean SSL = System.getProperty("ssl") != null;
    static final String HOST = System.getProperty("host", "127.0.0.1");
    static final int PORT = Integer.parseInt(System.getProperty("port", "8007"));
    static final int SIZE = Integer.parseInt(System.getProperty("size", "256"));

    public static void main(String[] args) throws Exception {
        // Configure SSL.git
        final SslContext sslCtx;
        if (SSL) {
            sslCtx = SslContextBuilder.forClient()
                .trustManager(InsecureTrustManagerFactory.INSTANCE).build();
        } else {
            sslCtx = null;
        }

        // Configure the client.
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group)
             .channel(NioSocketChannel.class)
             .option(ChannelOption.TCP_NODELAY, true)
             .handler(new ChannelInitializer<SocketChannel>() {
                 @Override
                 public void initChannel(SocketChannel ch) throws Exception {
                     ChannelPipeline p = ch.pipeline();
                     if (sslCtx != null) {
                         p.addLast(sslCtx.newHandler(ch.alloc(), HOST, PORT));
                     }
                     //p.addLast(new LoggingHandler(LogLevel.INFO));
                     p.addLast(new EchoClientHandler());
                 }
             });

            // Start the client.
            ChannelFuture f = b.connect(HOST, PORT).sync();

            // Wait until the connection is closed.
            f.channel().closeFuture().sync();
        } finally {
            // Shut down the event loop to terminate all threads.
            group.shutdownGracefully();
        }
    }
}

客户端处理类 EchoClientHandler

public class EchoClientHandler extends ChannelInboundHandlerAdapter {

    private final ByteBuf firstMessage;

    /**
     * Creates a client-side handler.
     */
    public EchoClientHandler() {
        firstMessage = Unpooled.buffer(EchoClient.SIZE);
        for (int i = 0; i < firstMessage.capacity(); i ++) {
            firstMessage.writeByte((byte) i);
        }
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) {
        ctx.writeAndFlush(firstMessage);
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) {
        ctx.write(msg);
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) {
       ctx.flush();
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        // Close the connection when an exception is raised.
        cause.printStackTrace();
        ctx.close();
    }
}