1.ServerBootstrap

ServerBootstrap引导服务端启动流程:

//主EventLoopGroup
NioEventLoopGroup master = new NioEventLoopGroup();
//从EventLoopGroup
NioEventLoopGroup worker = new NioEventLoopGroup();
//服务端引导类
ServerBootstrap bootstrap = new ServerBootstrap();
//配置主从EventLoopGroup
bootstrap.group(master, worker);
//channel选项配置
bootstrap.option(ChannelOption.SO_KEEPALIVE, true)
  .option(ChannelOption.CONNECT_TIMEOUT_MILLIS,5000);
bootstrap.channel(NioServerSocketChannel.class);
//主EventLoopGroup ChannelHandler配置
bootstrap.handler(new ChannelInboundHandlerAdapter(){
  @Override
  public void channelRegistered(ChannelHandlerContext ctx) throws Exception {
    System.out.println("Master:" + ctx.channel().eventLoop().toString());
    super.channelRegistered(ctx);
  }
});
//从EventLoopGroup ChannelHandler配置
bootstrap.childHandler(new ChannelInitializer<SocketChannel>() {
  @Override
  protected void initChannel(SocketChannel ch) throws Exception {
    System.out.println("Child:" + ch.eventLoop().toString());
  }
});
//调用bind方法开始监听端口8888
ChannelFuture future = bootstrap.bind(8888).sync();
future.channel().closeFuture().sync();

master.shutdownGracefully().sync();

以上代码使用的是Netty框架中经典的主从事件驱动模式

2.服务端启动过程

1. main方法调用ServerBootstrap.bind()方法

2. validate()方法验证必要配置参数

3. 调用AbstractBootstrap.initAndRegister()方法

4. 调用channelFactory.newChannel()方法创建Channel实例

5. ServerBootstrap.init()初始化Channel实例，配置ChannelOption、attributes；在Channel的pipeline中配置默认的ChannelHandler实例

6. 将Channel实例注册到主EventLoopGroup中并返回ChannelFuture

7. 注册ChannelFuture回调，在完成后调用channel.bind()方法完成端口监听

3.具体步骤分析

1.创建服务端Channel
2.初始化服务端Channel
3.注册Selector
4.端口绑定
5.触发读事件

3.1 创建服务端Channel

AbstractBootstrap.bind()

1. validate(): 验证必要配置参数
2. AbstractBootstrap.doBind()

AbstractBootstrap.initAndRegister()

1. 利用反射创建Channel, 得到NioServerSocketChannel
2. 初始化channel中的一些参数

AbstractBootstrap.channel() 反射创建Channel

利用反射创建channel, 得到ReflectiveChannelFactory, 调用channelFactory利用工厂模式, 最后生成NioServerSocketChannel

3.2 初始化服务端Channel

ServerBootstrap.init() 初始化一些基本参数

初始化一些Options和Attrs和group和handler的参数

    @Override
    void init(Channel channel) throws Exception {
        final Map<ChannelOption<?>, Object> options = options0();
        synchronized (options) {
            setChannelOptions(channel, options, logger);
        }

        final Map<AttributeKey<?>, Object> attrs = attrs0();
        synchronized (attrs) {
            for (Entry<AttributeKey<?>, Object> e: attrs.entrySet()) {
                @SuppressWarnings("unchecked")
                AttributeKey<Object> key = (AttributeKey<Object>) e.getKey();
                channel.attr(key).set(e.getValue());
            }
        }

        ChannelPipeline p = channel.pipeline();

        final EventLoopGroup currentChildGroup = childGroup;
        final ChannelHandler currentChildHandler = childHandler;
        final Entry<ChannelOption<?>, Object>[] currentChildOptions;
        final Entry<AttributeKey<?>, Object>[] currentChildAttrs;
        synchronized (childOptions) {
            currentChildOptions = childOptions.entrySet().toArray(newOptionArray(0));
        }
        synchronized (childAttrs) {
            currentChildAttrs = childAttrs.entrySet().toArray(newAttrArray(0));
        }

        p.addLast(new ChannelInitializer<Channel>() {
            @Override
            public void initChannel(final Channel ch) throws Exception {
                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));
                    }
                });
            }
        });
    }

设置 currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs

在Channel的pipeline中配置默认的ChannelHandler实例

ServerBootstrapAcceptor 添加连接器, ServerBootstrapAcceptor本质是一个handler

3.3 注册selector

bind -> initAndRegister -> AbstractChannel.register -> this.eventLoop = eventLoop, register0 实际注册 -> doRegister(), invokeHandlerAddedIfNeeded(), fireChannelRegistered() 传播事件

AbstractChannel.AbstractUnsafe.register()

register0()

AbstractNioChannel.doRegister()

上面有javaChannel.register(), 利用jdk底层去创建selector

3.4 端口绑定

bind() -> doBind() -> doBind0() -> AbstracChannel,bind() -> DefaultChannelPipeline.bind() -> AbstractChannlHandlerContext.bind() -> AbstractChannlHandlerContext.invokeBind() -> DefaultChannelPipeline.HeadContext.bind() -> NioSocketChannel.doBind0(), pipeline.fireChannelActive();

最后将会调用DefaultChannelPipeline.HeadContext.bind(), 因为DefaultChannelPipeline在初始化时会设置pipeline队列的首尾分别为DefaultChannelPipeline.HeadContext与DefaultChannelPipeline.TailContext
bind()在Pipeline中走的是出站方法，是从管道的后面向前走，最后到达管道头部的ChannelHandler(也就是DefaultChannelPipeline.HeadContext)，这一过程会调用同一方向上所有ChannelHandler的bind()事件。

AbstractBootstrap.doBind0(): 添加一个任务至EventLoop中, 最后将会调用DefaultChannelPipeline.HeadContext.bind()方法

AbstractChannlHandlerContext.invokeBind()

DefaultChannelPipeline.HeadContext.bind() -> AbstractChannel.AbstractUnsafe.bind()

        @Override
        public final void bind(final SocketAddress localAddress, final ChannelPromise promise) {
            assertEventLoop();
            
            if (!promise.setUncancellable() || !ensureOpen(promise)) {
                return;
            }
            
            boolean wasActive = isActive();
            try {
                doBind(localAddress);
            } catch (Throwable t) {
                safeSetFailure(promise, t);
                closeIfClosed();
                return;
            }

            if (!wasActive && isActive()) {
                invokeLater(new Runnable() {
                    @Override
                    public void run() {
                        pipeline.fireChannelActive();
                    }
                });
            }

            safeSetSuccess(promise);
        }

1. NioSocketChannel.doBind() -> NioSocketChannel.doBind0()
2. pipeline.fireChannelActive()

通过在pipline中的层层传递, 现在来到了最终执行bind操作的终点, 执行bind方法,

可以通过SocketUtils.bind() 绑定JDK底层的端口

3.5 服务端的读事件

最后如果触发了一个事件的话, 会调用Channel.read()事件(AbstractNioChannel.doBeginRead()), 这个事件对于服务端来说就是一个新的连接接入。

AbstractChannel.AbstractUnsafe.bind()

HeadContext.channelActive()

这个tail.read(), 触发的是beginRead()方法

AbstractUnsafe.beginRead()

AbstractNioChannel.doBeginRead()

这里的readInterestOp就是Acept事件

服务端端口绑定成功, 触发一个Acept事件, 然后调用channel.read()事件, 对于服务端来说就相当于可以读了, 可以读取一个新的连接。