我们不难发现基于Java Nio创建一个Server，主要分为以下几步：
创建一个ServerSocketChannel设置io模型，阻塞或者非阻塞 serverChannel.configureBlocking(false);创建selector多路复用器，注册监听OP_ACCEPT事件那么，我们那跟踪以下netty究竟是在哪做的这些封装，接下来我们将示例如何debug代码，追踪echoServer的启动调用过程。
首先我们看netty EchoServer中bootstrap.bind(new InetSocketAddress(port))方法，跟进来，我们看到它调用了如下方法：
public Channel bind(final SocketAddress localAddress) { //异步绑定，返回一个ChannelFuture ChannelFuture future = bindAsync(localAddress); // Wait for the future. future.awaitUninterruptibly(); if (!future.isSuccess()) { future.getChannel().close().awaitUninterruptibly(); throw new ChannelException("Failed to bind to: " + localAddress, future.getCause()); } return future.getChannel(); }我们继续跟进去bindAsync方法：
public ChannelFuture bindAsync(final SocketAddress localAddress) { if (localAddress == null) { throw new NullPointerException("localAddress"); } Binder binder = new Binder(localAddress); ChannelHandler parentHandler = getParentHandler(); ChannelPipeline bossPipeline = pipeline(); bossPipeline.addLast("binder", binder); if (parentHandler != null) { bossPipeline.addLast("userHandler", parentHandler); } // getFactory()方法返回的就是我们在初始化ServerBootstrap传入的NioServerSocketChannelFactory Channel channel = getFactory().newChannel(bossPipeline); final ChannelFuture bfuture = new DefaultChannelFuture(channel, false); binder.bindFuture.addListener(new ChannelFutureListener() { public void operationComplete(ChannelFuture future) throws Exception { if (future.isSuccess()) { bfuture.setSuccess(); } else { // Call close on bind failure bfuture.getChannel().close(); bfuture.setFailure(future.getCause()); } } }); return bfuture; }在bindAsync方法中，我们通过Channel channel = getFactory().newChannel(bossPipeline);获取了一个channel。在初始化Serverbootstrap的时候我们传入了NioServerSocketChannelFactory，NioServerSocketChannelFactory是创建NioServerSocketChannel的工厂方法，所以这里我们获取的channel的实现是NioServerSocketChannel。下面，我们要看NioServerSocketChannel里面做了些什么？我们来看NioServerSocketChannel的构造方法： NioServerSocketChannel( ChannelFactory factory, ChannelPipeline pipeline, ChannelSink sink, Boss boss, WorkerPool\u0026lt;NioWorker\u0026gt; workerPool) { super(factory, pipeline, sink); // boss 是早期版本netty用来处理accept连接的线程，仅仅使用了单线程，后来的版本中用了EventLoop，而且也改成了线程池的模型，也就是EventLoopGroup this.boss = boss; // workerPool就是netty用来处理io的线程池， this.workerPool = workerPool; try { // 创建了ServerSocketChannel socket = ServerSocketChannel.open(); } catch (IOException e) { throw new ChannelException( "Failed to open a server socket.", e); } try { // 设置为非阻塞模型 socket.configureBlocking(false); } catch (IOException e) { try { socket.close(); } catch (IOException e2) { if (logger.isWarnEnabled()) { logger.warn( "Failed to close a partially initialized socket.", e2); } } throw new ChannelException("Failed to enter non-blocking mode.", e); } // config = new DefaultServerSocketChannelConfig(socket.socket()); //调用Channels.fireChannelOpen(this) fireChannelOpen(this); }