ServerBootstrap 为 netty 建立服务端的辅助类, 以 NIO为例，创建代码如下：
public static void main(String[] args) throws Exception { ServerBootstrap bs = new ServerBootstrap(); bs.group(new NioEventLoopGroup(1), new NioEventLoopGroup()) .channel(NioServerSocketChannel.class) .childHandler(new ChannelInitializer<Channel>() { @Override protected void initChannel(Channel ch) throws Exception { ch.pipeline() .addLast(new HttpServerCodec()) .addLast(new HttpObjectAggregator(65535)) .addLast(new Controller()); } }).bind(8080).sync().channel().closeFuture().sync(); }
核心参数如下：
//配置属性，如 SO_KEEPALIVE 等private final ServerBootstrapConfig config = new ServerBootstrapConfig(this);
//acceot 的 子channel所绑定的 事件循环组" private volatile EventLoopGroup childGroup; private volatile ChannelHandler childHandler;
初始化流程主要为 绑定本地端口 -> 注册自身到 EventLoop ， 并注册 accept 和 read 事件 -> EventLoop的主循环中会不断的select注册的channel的事件，并处理。
首先执行绑定，核心逻辑位于 io.netty.bootstrap.AbstractBootstrap.doBind(SocketAddress) 和 io.netty.bootstrap.AbstractBootstrap.initAndRegister()中
private ChannelFuture doBind(final SocketAddress localAddress) { final ChannelFuture regFuture = initAndRegister(); ..........if (regFuture.isDone()) { // At this point we know that the registration was complete and successful. ChannelPromise promise = channel.newPromise();
//绑定逻辑 doBind0(regFuture, channel, localAddress, promise); return promise; } else { // Registration future is almost always fulfilled already, but just in case it's not. final PendingRegistrationPromise promise = new PendingRegistrationPromise(channel); regFuture.addListener(new ChannelFutureListener() { @Override public void operationComplete(ChannelFuture future) throws Exception { Throwable cause = future.cause(); if (cause != null) { // Registration on the EventLoop failed so fail the ChannelPromise directly to not cause an // IllegalStateException once we try to access the EventLoop of the Channel. promise.setFailure(cause); } else { // Registration was successful, so set the correct executor to use. // See https://github.com/netty/netty/issues/2586 promise.registered(); doBind0(regFuture, channel, localAddress, promise); } } }); return promise; } }
先来看 initAndRegister ， 核心逻辑就是利用channelFactory初始化一个NioServerSocketChannel实例，并为其设置上config中的参数，然后将其注册到EventLoop中，实际上是委托的channel的Unsafe来实现注册的，核心逻辑位于 AbstractUnsafe.register0 中 完成注册
final ChannelFuture initAndRegister() { Channel channel = null; try {
//本例子中实际调用的是 NioServerSocketChannel的构造参数， 并为其设置感兴趣的事件类型为 OP_ACCEPT channel = channelFactory.newChannel(); init(channel); } catch (Throwable t) { if (channel != null) { // channel can be null if newChannel crashed (eg SocketException("too many open files")) channel.unsafe().closeForcibly(); } // as the Channel is not registered yet we need to force the usage of the GlobalEventExecutor return new DefaultChannelPromise(channel, GlobalEventExecutor.INSTANCE).setFailure(t); } ChannelFuture regFuture = config().group().register(channel); if (regFuture.cause() != null) { if (channel.isRegistered()) { channel.close(); } else { channel.unsafe().closeForcibly(); } } return regFuture; }
1 void init(Channel channel) throws Exception { 2 //设置属性 15 .......... 17 p.addLast(new ChannelInitializer<Channel>() { 30 @Override 31 public void initChannel(final Channel ch) throws Exception { 32 final ChannelPipeline pipeline = ch.pipeline(); 33 ChannelHandler handler = config.handler(); 34 if (handler != null) { 35 pipeline.addLast(handler); 36 } 37 38 ch.eventLoop().execute(new Runnable() { 39 @Override 40 public void run() { //为NioServerSocketChannel 设置一个 默认的 channelhandler ： ServerBootstrapAcceptor ， 当发生 accept事件时，将 accept的channel注册到 childEventLoop中 41 pipeline.addLast(new ServerBootstrapAcceptor( 42 ch, currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs)); 43 } 44 }); 45 } 46 }); 47 }
private void register0(ChannelPromise promise) { try { // check if the channel is still open as it could be closed in the mean time when the register // call was outside of the eventLoop if (!promise.setUncancellable() || !ensureOpen(promise)) { return; } boolean firstRegistration = neverRegistered;
//执行channel到 eventloop的 selector doRegister(); neverRegistered = false; registered = true; // Ensure we call handlerAdded(...) before we actually notify the promise. This is needed as the // user may already fire events through the pipeline in the ChannelFutureListener. pipeline.invokeHandlerAddedIfNeeded(); safeSetSuccess(promise);
//触发 InboundChannelHnader.channelRegistered 事件
pipeline.fireChannelRegistered();
// Only fire a channelActive if the channel has never been registered. This prevents firing // multiple channel actives if the channel is deregistered and re-registered. if (isActive()) { if (firstRegistration) {
//触发channelActive事件，并会为 channel 绑定上 read 事件 pipeline.fireChannelActive(); } else if (config().isAutoRead()) { // This channel was registered before and autoRead() is set. This means we need to begin read // again so that we process inbound data. // // See https://github.com/netty/netty/issues/4805 beginRead(); } } } catch (Throwable t) { // Close the channel directly to avoid FD leak. closeForcibly(); closeFuture.setClosed(); safeSetFailure(promise, t); } }
initAndRegister注册成功后,开始执行真正的绑定端口逻辑，核心逻辑位于 NioSocketChannel.doBind0(SocketAddress) 中
private void doBind0(SocketAddress localAddress) throws Exception { if (PlatformDependent.javaVersion() >= 7) { SocketUtils.bind(javaChannel(), localAddress); } else { SocketUtils.bind(javaChannel().socket(), localAddress); } }
至此 绑定个成功， 当触发 ACCEPT 事件时， 会触发 NioServerSocketChannel.doReadMessages -> ServerBootstrapAcceptor.channelRead , 并将 子channel 注册到 childEventLoop中
public void channelRead(ChannelHandlerContext ctx, Object msg) { final Channel child = (Channel) msg; child.pipeline().addLast(childHandler); setChannelOptions(child, childOptions, logger); for (Entry<AttributeKey<?>, Object> e: childAttrs) { child.attr((AttributeKey<Object>) e.getKey()).set(e.getValue()); } try {
//注册channel childGroup.register(child).addListener(new ChannelFutureListener() { @Override public void operationComplete(ChannelFuture future) throws Exception { if (!future.isSuccess()) { forceClose(child, future.cause()); } } }); } catch (Throwable t) { forceClose(child, t); } }