1. netty在哪里调用jdk底层的socket去创建netty服务端的socket。
2. 在哪里accept连接。
服务端的启动：
1. 调用jdk底层的api去创建jdk的服务端的channel。Netty封装成自己的channel同时创建一些组件绑定在这个channel上面。
2. 初始化服务端的channel。
3. 注册selector，netty将jdk底层的channel注册到事件轮询器selector上面，并把服务端的channel作为attachment附加到jdk底层的channel上面，有事件轮询出来的时候就可以直接拿这个attachment，这个attachment就是netty封装的服务端的channel。
4. 端口绑定，调用jdk底层的api作为端口的监听。
1. 创建服务端的channel：
ChannelFuture f = b.bind(8888).sync();//服务端创建channel的入口
final ChannelFuture regFuture = initAndRegister(); //创建服务端的channel
final ChannelFuture initAndRegister() {
Channel channel = null;
try {
channel = channelFactory.newChannel(); //.channel方法设置channelFactory，channelFactory是ReflectiveChannelFactory
init(channel);
}
public class ReflectiveChannelFactory<T extends Channel> implements ChannelFactory<T> {
public ReflectiveChannelFactory(Class<? extends T> clazz) {
if (clazz == null) {
throw new NullPointerException("clazz");
}
this.clazz = clazz;
}
@Override
public T newChannel() { //newChannel方法
try {
return clazz.newInstance(); //通过反射创建channel，clazz是NioServerSocketChannel.class，newInstance()调用的是构造函数
} catch (Throwable t) {
throw new ChannelException("Unable to create Channel from class " + clazz, t);
}
}
}
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class) //分析.channel方法，传入NioServerSocketChannel通过反射方式调用NioServerSocketChannel类的构造函数
AbstractBootstrap类：
public B channel(Class<? extends C> channelClass) { //channelClass是传进来的NioServerSocketChannel.class
if (channelClass == null) {
throw new NullPointerException("channelClass");
}
return channelFactory(new ReflectiveChannelFactory<C>(channelClass)); //通过ReflectiveChannelFactory构造函数把channelClass封装成ReflectiveChannelFactory，设置channelFactory
}
public B channelFactory(ChannelFactory<? extends C> channelFactory) {
if (channelFactory == null) {
throw new NullPointerException("channelFactory");
}
if (this.channelFactory != null) {
throw new IllegalStateException("channelFactory set already");
}
this.channelFactory = channelFactory; //设置channelFactory
return (B) this;
}
NioServerSocketChannel构造函数：
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() { //构造函数
this(newSocket(DEFAULT_SELECTOR_PROVIDER)); //newSocket创建jdk底层的Channel，服务端的channel就创建完毕了
}
public NioServerSocketChannel(ServerSocketChannel channel) {
super(null, channel, SelectionKey.OP_ACCEPT);
config = new NioServerSocketChannelConfig(this, javaChannel().socket()); // this是NioServerSocketChannel也就是netty服务端的channel，
}
super(null, channel, SelectionKey.OP_ACCEPT); //跟进去
AbstractNioChannel类：
protected AbstractNioChannel(Channel parent, SelectableChannel ch, int readInterestOp) {
super(parent);
this.ch = ch; //通过newSocket创建出来的jdk底层的channel，
this.readInterestOp = readInterestOp;
try {
ch.configureBlocking(false);//设置服务端的channel非阻塞模式，
} catch (IOException e) {
try {
ch.close();
} catch (IOException e2) {
if (logger.isWarnEnabled()) {
logger.warn("Failed to close a partially initialized socket.", e2);
}
}
throw new ChannelException("Failed to enter non-blocking mode.", e);
}
}
//channel有服务端和客户端的channel，都继承自AbstractChannel，
protected AbstractChannel(Channel parent) {
this.parent = parent;
id = newId();//channel唯一的表示
unsafe = newUnsafe();//channel底层tcp相关的操作
pipeline = newChannelPipeline();
}