ChannelGroup

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,

一个线程安全的Set容器提供对Channels的操作

you can categorize Channels into a meaningful group (e.g. on a per-service or per-state basis.) A closed Channel is

你可以把Channels归类为一个有意义的组，Channel的closed关闭会自动的从集合中移除整个Channel，

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.

因此你不必担心一个Channel会同时属于不同的ChannelGroup

Broadcast a message to multiple Channels

广播一条消息到多个Channel

 

If you need to broadcast a message to more than one Channel, you can add the Channels associated with the recipients

如果你需要广播一条消息到多个Channel，你可以添加Channels 

and call write(Object):

 ChannelGroup recipients = new DefaultChannelGroup();
 recipients.add(channelA);
 recipients.add(channelB);
 ..
 recipients.write(ChannelBuffers.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();

 public static void main(String[] args) throws Exception {
     ServerBootstrap b = new ServerBootstrap(..);
     ...

     // Start the server
     b.getPipeline().addLast("handler", new MyHandler());
     Channel serverChannel = b.bind(..);
     allChannels.add(serverChannel);

     ... Wait until the shutdown signal reception ...

     // Close the serverChannel and then all accepted connections.
     allChannels.close().awaitUninterruptibly();
     b.releaseExternalResources();
 }

 public class MyHandler extends SimpleChannelUpstreamHandler {
     @Override
     public void channelOpen(ChannelHandlerContext ctx, ChannelStateEvent e) {
         // Add all open channels to the global group so that they are
         // closed on shutdown.
         allChannels.add(e.getChannel());
     }
 }