前文Netty源码分析系列--3. 服务器启动ServerBootStrap分析中介绍了对ServerBootStrap的多个变量赋值后，下一步就要绑定端口号启动服务器。
ChannelFuture channelFuture = serverBootstrap.bind(8899).sync();
调用bind(8899)进入抽象类AbstractBootStrap的doBind方法:
private ChannelFuture doBind(final SocketAddress localAddress) {
final ChannelFuture regFuture = initAndRegister();
final Channel channel = regFuture.channel();
if (regFuture.cause() != null) {
return regFuture;
}
if (regFuture.isDone()) {
ChannelPromise promise = channel.newPromise();
doBind0(regFuture, channel, localAddress, promise);
return promise;
} else {
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) {
promise.setFailure(cause);
} else {
promise.registered();
doBind0(regFuture, channel, localAddress, promise);
}
}
});
return promise;
}
}
其中关键的方法是：
intAndRegister()- 对
ChannelFuture类型的对象regFuture添加监听器，当IO操作完成时执行回调方法operationComplete。
1 . 先关注第1行initAndRegister方法如下：其中channelFactory.newChannel()就是使用之前channel方法中创建的ReflectiveChannelFactory通过反射新建NioServerSocketChannel实例。
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();
}
}
return regFuture;
}
NioServerSocketChannel类的构造函数：静态变量DEFAULT_SELECTOR_PROVIDER使用了NIO Selector Provider，构造函数中调用静态方法newSocket。
使用
provider.openServerSocketChannel()创建NioServerSocketChannel。
private static final SelectorProvider DEFAULT_SELECTOR_PROVIDER = SelectorProvider.provider();
private static ServerSocketChannel newSocket(SelectorProvider provider) {
try {
return provider.openServerSocketChannel();
} catch (IOException e) {
throw new ChannelException(
"Failed to open a server socket.", e);
}
}
public NioServerSocketChannel() {
this(newSocket(DEFAULT_SELECTOR_PROVIDER));
}
2. initAndRegister中使用ChannelFactory创建完Channel后，调用了init进行初始化。
void init(Channel channel) throws Exception {
//以上省略......
ChannelPipeline p = channel.pipeline();
final EventLoopGroup currentChildGroup = childGroup;
final ChannelHandler currentChildHandler = childHandler;
//省略部分代码......
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));
}
});
}
});
}
获得channel对象的pipleline，如果有配置handler对象如LoggingHandler(LogLevel.INFO)，会加入到pipeline中。
注意：这里出现了一个类
ServerBootstrapAcceptor，稍后会介绍。
3. initAndRegister中：
ChannelFuture regFuture = config().group().register(channel);
上面代码group()获得bossGroup对象，并将channel注册到该EventLoopGroup。
