Netty:options和configs

在使用Netty时，初始化服务端或客户端时，我们经常会看到如下代码
Bootstrap b = new Bootstrap();
......
b.channel(NioSocketChannel.class).option(ChannelOption.TCP_NODELAY, true);通过option方法设置一些选项（参数），它其实是一个Map，维护这键值对，option方法在AbstractBootstrap类中private final Map<ChannelOption<?>, Object> options = new LinkedHashMap<ChannelOption<?>, Object>();

@SuppressWarnings("unchecked")
public <T> B option(ChannelOption<T> option, T value) {
if (option == null) {
throw new NullPointerException("option");
}
if (value == null) {
synchronized (options) {
options.remove(option);
}
} else {
synchronized (options) {
options.put(option, value);
}
}
return (B) this;
}如果value是null，就会从options中删除这个对象，我们之前传入的ChannelOption.TCP_NODELAY，作为key值，true 作为value值。ChannelOption有很多选项可以设置，具体可以参见Netty文档http://netty.io/4.1/api/io/netty/channel/ChannelOption.html
当我们要使用设置好的option时，其实是通过Channel的Config去访问的，那我们设置的option是怎样写入Config的呢？以NioSocketChannel为例，初始化时
public NioSocketChannel(Channel parent, SocketChannel socket) {
super(parent, socket);
config = new NioSocketChannelConfig(this, socket.socket());
}这里会创建一个NioSocketChannelConfig对象，然后在BootStrap的init方法中，有这样的过程@Override
@SuppressWarnings("unchecked")
void init(Channel channel) throws Exception {
ChannelPipeline p = channel.pipeline();
......
final Map<ChannelOption<?>, Object> options = options();
synchronized (options) {
for (Entry<ChannelOption<?>, Object> e: options.entrySet()) {
try {
if (!channel.config().setOption((ChannelOption<Object>) e.getKey(), e.getValue())) {
logger.warn("Unknown channel option: " + e);
}
} catch (Throwable t) {
logger.warn("Failed to set a channel option: " + channel, t);
}
}
}

......
}我们看到，它遍历channe的options，然后通过config对象的setOption去设置config中的属性，如DefaultChannelConfig中 @Override
@SuppressWarnings("deprecation")
public <T> boolean setOption(ChannelOption<T> option, T value) {
validate(option, value);

if (option == CONNECT_TIMEOUT_MILLIS) {
setConnectTimeoutMillis((Integer) value);
} else if (option == MAX_MESSAGES_PER_READ) {
setMaxMessagesPerRead((Integer) value);
} else if (option == WRITE_SPIN_COUNT) {
setWriteSpinCount((Integer) value);
} else if (option == ALLOCATOR) {
setAllocator((ByteBufAllocator) value);
} else if (option == RCVBUF_ALLOCATOR) {
setRecvByteBufAllocator((RecvByteBufAllocator) value);
} else if (option == AUTO_READ) {
setAutoRead((Boolean) value);
} else if (option == AUTO_CLOSE) {
setAutoClose((Boolean) value);
} else if (option == WRITE_BUFFER_HIGH_WATER_MARK) {
setWriteBufferHighWaterMark((Integer) value);
} else if (option == WRITE_BUFFER_LOW_WATER_MARK) {
setWriteBufferLowWaterMark((Integer) value);
} else if (option == MESSAGE_SIZE_ESTIMATOR) {
setMessageSizeEstimator((MessageSizeEstimator) value);
} else {
return false;
}

return true;
}DefaultSocketChannelConfig中道理一样。

NioSocketChannelConfig的继承关系如下
NioSocketChannelConfig extends DefaultSocketChannelConfig extends DefaultChannelConfig implements ChannelConfig
DefaultChannelConfig中是一般性的选项，NioSocketChannelConfig是与socket相关的设置，ChannelOption中以SO开头的都是与此相关的。
使用相关option时，也是通过config的getOption去获取的。当然Config对象也设置了一些属性，和这些option相关联，可以通过方法直接访问到。 public <T> T getOption(ChannelOption<T> option) {
if (option == null) {
throw new NullPointerException("option");
}

if (option == CONNECT_TIMEOUT_MILLIS) {
return (T) Integer.valueOf(getConnectTimeoutMillis());
}
......
return null;
}比如我们设置超时时间ChannelOption.CONNECT_TIMEOUT_MILLIS，那么在AbstractNioChannel的connect方法中就能看到它的踪影： public final void connect(
......
try {
......
boolean wasActive = isActive();
if (doConnect(remoteAddress, localAddress)) {
fulfillConnectPromise(promise, wasActive);
} else {
connectPromise = promise;
requestedRemoteAddress = remoteAddress;

// Schedule connect timeout.
int connectTimeoutMillis = config().getConnectTimeoutMillis();
if (connectTimeoutMillis > 0) {
connectTimeoutFuture = eventLoop().schedule(new OneTimeTask() {
@Override
public void run() {
ChannelPromise connectPromise = AbstractNioChannel.this.connectPromise;
ConnectTimeoutException cause =
new ConnectTimeoutException("connection timed out: " + remoteAddress);
if (connectPromise != null && connectPromise.tryFailure(cause)) {
close(voidPromise());
}
}
}, connectTimeoutMillis, TimeUnit.MILLISECONDS);
}
......
}
} catch (Throwable t) {
promise.tryFailure(annotateConnectException(t, remoteAddress));
closeIfClosed();
}
}config().getConnectTimeoutMillis()获取设置，然后启动定时任务，等待超时。