Netty 核心源码解读 —— ServerBootstrap 篇

这里?NioServerSocketChannel.class?通过 ReflectiveChannelFactory 进行了实例化，然后赋值给了 AbstractBootstrap 的 channelFactory。

接下来是?childHandler()?方法。

ServerBootstrap.java`

private volatile ChannelHandler childHandler;

public ServerBootstrap childHandler(ChannelHandler childHandler) { this.childHandler = ObjectUtil.checkNotNull(childHandler, "childHandler"); `return this;``}

这里是对 ServerBootstrap 的 childHandler 赋值。

最后是?childOption()?方法。

ServerBootstrap.java`

private final Map<ChannelOption<?>, Object> childOptions = new LinkedHashMap<ChannelOption<?>, Object>();

public <T> ServerBootstrap childOption(ChannelOption<T> childOption, T value) { ObjectUtil.checkNotNull(childOption, "childOption"); synchronized (childOptions) { if (value == null) { childOptions.remove(childOption); } else { childOptions.put(childOption, value); } } `return this;``}

这里 childOptions 维护了 TCP 的参数设置。

简言之?bootstrap.group().channel().childHandler().childOption()?就是在构建 Netty Server 的各种参数，下面再来看?bootstrap.bind(port).sync()。

首先是?bind()?方法。

AbstractBootstrap.java`

public ChannelFuture bind(int inetPort) { return bind(new InetSocketAddress(inetPort));``}

public ChannelFuture bind(SocketAddress localAddress) { validate(); return doBind(ObjectUtil.checkNotNull(localAddress, "localAddress"));``}

public B validate() { if (group == null) { throw new IllegalStateException("group not set"); } if (channelFactory == null) { throw new IllegalStateException("channel or channelFactory not set"); } `return self();``}

这里的?validate()?方法对 AbstractBootstrap 的 group 和 channelFactory 进行非空校验，之后调用?doBind()?方法。

AbstractBootstrap.java`

private ChannelFuture doBind(final SocketAddress localAddress) { final ChannelFuture regFuture = initAndRegister(); final Channel channel = regFuture.channel(); if (regFuture **《一线大厂Java面试题解析+后端开发学习笔记+最新架构讲解视频+实战项目源码讲义》无偿开源 威信搜索公众号【编程进阶路】** .cause() != null) { return regFuture; }

if (regFuture.isDone()) { // At this point we know that the registration was complete and successful. ChannelPromise promise = channel.newPromise(); 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; `}``}

首先看一下?initAndRegister()?方法。

AbstractBootstrap.java`

final ChannelFuture initAndRegister() { Channel channel = null; try { 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); } // as the Channel is not registered yet we need to force the usage of the GlobalEventExecutor return new DefaultChannelPromise(new FailedChannel(), GlobalEventExecutor.INSTANCE).setFailure(t); }

ChannelFuture regFuture = config().group().register(channel); if (regFuture.cause() != null) { if (channel.isRegistered()) { channel.close(); } else { channel.unsafe().closeForcibly(); } }

// If we are here and the promise is not failed, it's one of the following cases: // 1) If we attempted registration from the event loop, the registration has been completed at this point. // i.e. It's safe to attempt bind() or connect() now because the channel has been registered. // 2) If we attempted registration from the other thread, the registration request has been successfully // added to the event loop's task queue for later execution. // i.e. It's safe to attempt bind() or connect() now: // because bind() or connect() will be executed *after* the scheduled registration task is executed // because register(), bind(), and connect() are all bound to the same thread.

`return regFuture;``}

这里?channelFactory.newChannel()?调用的是 ReflectiveChannelFactory 的 newChannel 方法。

ReflectiveChannelFactory`

private final Constructor<? extends T> constructor;

public ReflectiveChannelFactory(Class<? extends T> clazz) {

ObjectUtil.checkNotNull(clazz, "clazz"); try { this.constructor = clazz.getConstructor(); } catch (NoSuchMethodException e) { throw new IllegalArgumentException("Class " + StringUtil.simpleClassName(clazz) + " does not have a public non-arg constructor", e); }``}

public T newChannel() { try { return constructor.newInstance(); } catch (Throwable t) { throw new ChannelException("Unable to create Channel from class " + constructor.getDeclaringClass(), t); `}``}

这里?constructor.newInstance()?是?NioServerSocketChannel.class?的一个实例。得到 channel 后，调用?init(channel)?进行初始化，一是给 options 和 attrs 赋值，二是构建 pipeline。

ServerBootstrap.java`

void init(Channel channel) { setChannelOptions(channel, newOptionsArray(), logger); setAttributes(channel, attrs0().entrySet().toArray(EMPTY_ATTRIBUTE_ARRAY));

ChannelPipeline p = channel.pipeline();

final EventLoopGroup currentChildGroup = childGroup; final ChannelHandler currentChildHandler = childHandler; final Entry<ChannelOption<?>, Object>[] currentChildOptions; synchronized (childOptions) { currentChildOptions = childOptions.entrySet().toArray(EMPTY_OPTION_ARRAY); } final Entry<AttributeKey<?>, Object>[] currentChildAttrs = childAttrs.entrySet().toArray(EMPTY_ATTRIBUTE_ARRAY);

p.addLast(new ChannelInitializer<Channel>() { @Override public void initChannel(final Channel ch) { final ChannelPipeline pipeline = ch.pipeline(); ChannelHandler handler = config.handler(); if (handler != null) { pipeline.addLast(handler); }

ch.eventLoop().execute(new Runnable() { @Override public void run() { pipeline.addLast(new ServerBootstrapAcceptor( ch, currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs)); } }); } `});``}

回到?initAndRegister()?方法中，init(channel)?之后是?register(channel)，该方法在 NioEventLoopGroup 的父类 MultithreadEventLoopGroup 中实现，我们在解读 NioEventLoop 源码时再分析。

MultithreadEventLoopGroup`

public ChannelFuture register(Channel channel) { `return next().register(channel);``}

看完?initAndRegister()，再回到?doBind()?接着看?doBind0()。

AbstractBootstrap`

private static void doBind0( final ChannelFuture regFuture, final Channel channel, final SocketAddress localAddress, final ChannelPromise promise) {

// This method is invoked before channelRegistered() is triggered. Give user handlers a chance to set up // the pipeline in its channelRegistered() implementation. channel.eventLoop().execute(new Runnable() { @Override public void run() { if (regFuture.isSuccess()) { channel.bind(localAddress, promise).addListener(ChannelFutureListener.CLOSE_ON_FAILURE); } else { promise.setFailure(regFuture.cause()); } } `});``}

这里?regFuture.isSuccess()?会执行?channel.bind(localAddress, promise).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);，否者执行?promise.setFailure(regFuture.cause());，这里的 promise 可以认为是一种特殊的 Future 对象。bind 是在 ChannelPipeline 里进行绑定的，我们在解读 ChannelPipeline 源码时再分析。