gistfile1.java

public class MyHandler extends ChannelInboundMessageHandlerAdapter<MyMessage> {

    private static final AttributeKey<MyState> STATE =
            new AttributeKey<MyState>("MyHandler.state");

    @Override
    public void channelRegistered(ChannelHandlerContext ctx) {
        ctx.attr(STATE).set(new MyState());
        ctx.fireChannelRegistered();
    }

    @Override
    public void messageReceived(ChannelHandlerContext ctx, MyMessage msg) {
        MyState state = ctx.attr(STATE).get();
    }
    ...
}