if (parentHandler != null) {
bossPipeline = pipeline();
bossPipeline.addLast("binder", binder);
bossPipeline.addLast("userHandler", parentHandler);
} else {
bossPipeline = new StaticChannelPipeline(binder);
}
//在new一个Channel时会调用Channels的fireChannelOpen,引发UpstreamChannelStateEvent事件
Channel channel = getFactory().newChannel(bossPipeline);