netty-ChannelGroup
public interface ChannelGroupextends Set<Channel>, Comparable<ChannelGroup>
A thread-safe Set that contains open Channels and provides various bulk operations on them. Using ChannelGroup, you can categorize Channels into a meaningful group (e.g. on a per-service or per-state basis.) A closed Channel is automatically removed from the collection, so that you don't need to worry about the life cycle of the added Channel. A Channelcan belong to more than one ChannelGroup.
Broadcast a message to multiple Channels
If you need to broadcast a message to more than one Channel, you can add the Channels associated with the recipients and call write(Object):
ChannelGroup recipients = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE); recipients.add(channelA); recipients.add(channelB); .. recipients.write(Unpooled.copiedBuffer( "Service will shut down for maintenance in 5 minutes.", CharsetUtil.UTF_8));
Simplify shutdown process with ChannelGroup
If both ServerChannels and non-ServerChannels exist in the same ChannelGroup, any requested I/O operations on the group are performed for the ServerChannels first and then for the others.
This rule is very useful when you shut down a server in one shot:
ChannelGroup allChannels =
new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);
public static void main(String[] args) throws Exception { ServerBootstrap b = new ServerBootstrap(..);
...
b.childHandler(new MyHandler());
// Start the server
b.getPipeline().addLast("handler", new MyHandler()); Channel serverChannel = b.bind(..).sync(); allChannels.add(serverChannel);
... Wait until the shutdown signal reception ...
// Close the serverChannel and then all accepted connections. allChannels.close().awaitUninterruptibly();
}
public class MyHandler extends ChannelHandlerAdapter { @Override
public void channelActive(ChannelHandlerContext ctx) {
// closed on shutdown. allChannels.add(ctx.channel());
super.channelActive(ctx);
}
}