【Netty源码学习】ServerBootStrap

上一篇博客【Netty源码学习】BootStrap中我们介绍了客户端使用的启动服务，接下来我们介绍一下服务端使用的启动服务。

总体来说ServerBootStrap有两个主要功能：

（1）调用父类AbstractBootStrap的initAndregister函数将NioServerSocketChannel注册到Selector中，上一篇博客中我们已经介绍了。

（2）调用父类的doBind0函数绑定端口，并在线程池中执行。

ServerBootStrap使用如下：

ServerBootstrap serverBootstrap = new ServerBootstrap().group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)
					.localAddress(port).childHandler(new ChannelInitializer<SocketChannel>() {

						@Override
						protected void initChannel(SocketChannel ch) throws Exception {
							 ch.pipeline().addLast("decoder", new StringDecoder());
	                            ch.pipeline().addLast("encoder", new StringEncoder());
	                            ch.pipeline().addLast(new ServerHandler());
						}
					}).option(ChannelOption.SO_BACKLOG, 128)
	                .childOption(ChannelOption.SO_KEEPALIVE, true);
			ChannelFuture future = serverBootstrap.bind(port).sync();   

在构造函数中只是一些参数值的设置，真正开始操作的地方是调用 serverBootstrap.bind(port).sync()，从bind函数开始来实现我们刚才讲的两个主要功能。

首先绑定端口函数调用。

	public ChannelFuture bind(int inetPort) {
        return bind(new InetSocketAddress(inetPort));
	}
	 public ChannelFuture bind(SocketAddress localAddress) {
        validate();
        if (localAddress == null) {
            throw new NullPointerException("localAddress");
        }
        return doBind(localAddress);
    }
    private ChannelFuture doBind(final SocketAddress localAddress) {
        final ChannelFuture regFuture = initAndRegister();
        final Channel channel = regFuture.channel();
        if (regFuture.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;
        }
    }

在绑定端口操作是我们会看到如下操作final ChannelFuture regFuture = initAndRegister();，initAndRegister就是实现Channel注册到Selector中，前一篇博客中我们已经介绍。接下来我们介绍doBind0函数，服务端绑定端口到本机服务器上。

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());
                }
            }
        });
    }

通过上面的代码我们知道doBind0的操作就是创建一个新线程，放到线程池中操作，通过Channel来绑定地址。