How do get a pointer to child channels from ServerBootStrap in Netty 4

Question

I'm trying to figure out how best to get a pointer to the channels spawned by my server bootstrap. The idea being that I might later do something like

childChannel.write(x);

This is the code I currently have.

    EventLoopGroup bossGroup = new NioEventLoopGroup(1);
    EventLoopGroup workerGroup = new NioEventLoopGroup();
    try {
        ServerBootstrap b = new ServerBootstrap(); 
        b.group(bossGroup, workerGroup)
                .channel(NioServerSocketChannel.class) 
                .childHandler(new ChannelInitializer<SocketChannel>() {                        @Override
                    public void initChannel(SocketChannel ch) throws Exception {
                        //ch.pipeline().addLast(new TimeEncoder(),new DiscardServerHandler());
                        ch.pipeline().addLast(
                                new ObjectEncoder(),
                                new ObjectDecoder(ClassResolvers.cacheDisabled(null)),
                                new ObjectEchoServerHandler());
                    }
                });

        ChannelFuture f = b.bind(port).sync();
        //f.channel() returns the NioServerSocketChannel ... not the child
        //@TODO need child channel...*********

Thanks!

Answer 1

You might try to use ChannelGroup (see API doc), for instance:

To place before you create your ServerBootstrap

ChannelGroup allChannels = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);

You might decide to change the EventExecutor to workerGroup too.

Then in your ObjectEchoServerHandler, your constructor could set this ChannelGroup

public class ObjectEchoServerHandler extends xxx {
   ChannelGroup allChannels;
   public ObjectEchoServerHandler(ChannelGroup allChannels) {
      this.allChannels = allChannels;
   }

   @Override
   public void channelActive(ChannelHandlerContext ctx) {
       // closed on shutdown.
       allChannels.add(ctx.channel());
       super.channelActive(ctx);
   }
}

And then you can use the group to send message to who you want, all or a specific one.