io.netty.channel.group

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();
 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();

 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());
     }
 }
 

Method Summary

Methods

Modifier and Type	Method and Description
ChannelGroupFuture	close() Closes all Channels in this group.
ChannelGroupFuture	disconnect() Disconnects all Channels in this group from their remote peers.
Channel	find(Integer id) Returns the Channel whose ID matches the specified integer.
String	name() Returns the name of this group.
ChannelGroupFuture	write(Object message) Writes the specified message to all Channels in this group.

Methods inherited from interface java.util.Set

add, addAll, clear, contains, containsAll, equals, hashCode, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray

Methods inherited from interface java.lang.Comparable

compareTo

Method Detail

name

String name()

Returns the name of this group. A group name is purely for helping you to distinguish one group from others.

find

Channel find(Integer id)

Returns the Channel whose ID matches the specified integer.

Returns:

the matching Channel if found. null otherwise.

write

ChannelGroupFuture write(Object message)

Writes the specified message to all Channels in this group. If the specified message is an instance of ByteBuf, it is automatically duplicated to avoid a race condition. Please note that this operation is asynchronous as ChannelOutboundInvoker.write(Object) is.

Returns:

the ChannelGroupFuture instance that notifies when the operation is done for all channels

disconnect

ChannelGroupFuture disconnect()

Disconnects all Channels in this group from their remote peers.

Returns:

the ChannelGroupFuture instance that notifies when the operation is done for all channels

close

ChannelGroupFuture close()

Closes all Channels in this group. If the Channel is connected to a remote peer or bound to a local address, it is automatically disconnected and unbound.

Returns:

the ChannelGroupFuture instance that notifies when the operation is done for all channels