类图：
类定义：
io.netty.channel.ChannelInboundHandlerAdapter
/** * Abstract base class for {@link ChannelInboundHandler} implementations which provide * implementations of all of their methods. * * <p> * This implementation just forward the operation to the next {@link ChannelHandler} in the * {@link ChannelPipeline}. Sub-classes may override a method implementation to change this. * </p> * <p> * Be aware that messages are not released after the {@link #channelRead(ChannelHandlerContext, Object)} * method returns automatically. If you are looking for a {@link ChannelInboundHandler} implementation that * releases the received messages automatically, please see {@link SimpleChannelInboundHandler}. * </p> */ public class ChannelInboundHandlerAdapter extends ChannelHandlerAdapter implements ChannelInboundHandler类图：
类定义：
io.netty.bootstrap.ServerBootstrap
/** * {@link Bootstrap} sub-class which allows easy bootstrap of {@link ServerChannel} * */ public class ServerBootstrap extends AbstractBootstrap<ServerBootstrap, ServerChannel>类图：
类定义：
io.netty.bootstrap.Bootstrap
/** * A {@link Bootstrap} that makes it easy to bootstrap a {@link Channel} to use * for clients. * * <p>The {@link #bind()} methods are useful in combination with connectionless transports such as datagram (UDP). * For regular TCP connections, please use the provided {@link #connect()} methods.</p> */ public class Bootstrap extends AbstractBootstrap<Bootstrap, Channel>类图：
下面就正式开始追源码。
创建SelectorSelector的创建起于这行代码EventLoopGroup bossGroup = new NioEventLoopGroup(1)
io.netty.channel.nio.NioEventLoopGroup
/** * Create a new instance using the specified number of threads, {@link ThreadFactory} and the * {@link SelectorProvider} which is returned by {@link SelectorProvider#provider()}. */ public NioEventLoopGroup(int nThreads) { this(nThreads, (Executor) null); } public NioEventLoopGroup(int nThreads, Executor executor) { this(nThreads, executor, SelectorProvider.provider()); }这里我们看到了熟悉的SelectorProvider.provider()，如果觉得陌生，建议回到上面快速上手java.nio的代码。
往里面追几层，就到了NioEventLoopGroup的父类 MultithreadEventExecutorGroup 。
io.netty.util.concurrent.MultithreadEventExecutorGroup
protected MultithreadEventExecutorGroup(int nThreads, Executor executor, EventExecutorChooserFactory chooserFactory, Object... args) { if (executor == null) { executor = new ThreadPerTaskExecutor(newDefaultThreadFactory()); } children = new EventExecutor[nThreads]; for (int i = 0; i < nThreads; i ++) { children[i] = newChild(executor, args); } }注意： 创建NioEventLoopGroup(int nThreads)时的参数nThreads就传到了上面代码中的children = new EventExecutor[nThreads]。看newChild(executor, args)做了什么。
io.netty.channel.nio.NioEventLoopGroup
@Override protected EventLoop newChild(Executor executor, Object... args) throws Exception { EventLoopTaskQueueFactory queueFactory = args.length == 4 ? (EventLoopTaskQueueFactory) args[3] : null; return new NioEventLoop(this, executor, (SelectorProvider) args[0], ((SelectStrategyFactory) args[1]).newSelectStrategy(), (RejectedExecutionHandler) args[2], queueFactory); }io.netty.channel.nio.NioEventLoop
NioEventLoop(NioEventLoopGroup parent, Executor executor, SelectorProvider selectorProvider, SelectStrategy strategy, RejectedExecutionHandler rejectedExecutionHandler, EventLoopTaskQueueFactory queueFactory) { super(parent, executor, false, newTaskQueue(queueFactory), newTaskQueue(queueFactory), rejectedExecutionHandler); this.provider = ObjectUtil.checkNotNull(selectorProvider, "selectorProvider"); this.selectStrategy = ObjectUtil.checkNotNull(strategy, "selectStrategy"); final SelectorTuple selectorTuple = openSelector(); this.selector = selectorTuple.selector; this.unwrappedSelector = selectorTuple.unwrappedSelector; }Selector的创建就发生在这行代码final SelectorTuple selectorTuple = openSelector();进去看看。