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。