Interface ChannelGroup

All Superinterfaces:
Collection<Channel>, Comparable<ChannelGroup>, Iterable<Channel>, Set<Channel>
All Known Implementing Classes:
DefaultChannelGroup
public interface ChannelGroup extends 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 Channel can 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 ChannelInboundHandlerAdapter {
    @Override
    public void channelActive(ChannelHandlerContext ctx) {
        // closed on shutdown.
        allChannels.add(ctx.channel());
        super.channelActive(ctx);
    }
}