Netty源码学习（五）ChannelInitializer

0. ChannelInitializer简介

1. ChannelInitializer类图

2. initChannel抽象方法

/**
* This method will be called once the {@link Channel} was registered. After the method returns this instance
* will be removed from the {@link ChannelPipeline} of the {@link Channel}.
*
* @param ch            the {@link Channel} which was registered.
* @throws Exception    is thrown if an error occurs. In that case it will be handled by
*                      {@link #exceptionCaught(ChannelHandlerContext, Throwable)} which will by default close
*                      the {@link Channel}.
*/
protected abstract void initChannel(C ch) throws Exception;

3. ChannelInitializer什么时候会被调用？

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));
}
});
}
});

/**
* {@inheritDoc} If override this method ensure you call super!
*/
@Override
public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
if (ctx.channel().isRegistered()) {
// This should always be true with our current DefaultChannelPipeline implementation.
// The good thing about calling initChannel(...) in handlerAdded(...) is that there will be no ordering
// surprises if a ChannelInitializer will add another ChannelInitializer. This is as all handlers
// will be added in the expected order.
            initChannel(ctx);
}
}

@SuppressWarnings("unchecked")
private boolean initChannel(ChannelHandlerContext ctx) throws Exception {
if (initMap.putIfAbsent(ctx, Boolean.TRUE) == null) { // Guard against re-entrance.
try {
initChannel((C) ctx.channel());//调用子类重写的initChannel方法
} catch (Throwable cause) {
// Explicitly call exceptionCaught(...) as we removed the handler before calling initChannel(...).
// We do so to prevent multiple calls to initChannel(...).
exceptionCaught(ctx, cause);
} finally {
remove(ctx);//将ChannelInitializer从pipeline中移除
}
return true;
}
return false;
}

/**
* This method will be called once the {@link Channel} was registered. After the method returns this instance
* will be removed from the {@link ChannelPipeline} of the {@link Channel}.
*
* @param ch            the {@link Channel} which was registered.
* @throws Exception    is thrown if an error occurs. In that case it will be handled by
*                      {@link #exceptionCaught(ChannelHandlerContext, Throwable)} which will by default close
*                      the {@link Channel}.
*/
protected abstract void initChannel(C ch) throws Exception;

private void remove(ChannelHandlerContext ctx) {
try {
ChannelPipeline pipeline = ctx.pipeline();
if (pipeline.context(this) != null) {
pipeline.remove(this);
}
} finally {
initMap.remove(ctx);
}
}

4. 总结