public interface Message {
  // your methods here
}

public class DataServerHandler extends SimpleChannelInboundHandler<Message> {

  private boolean loggedIn;

  @Override
  protected void messageReceived(ChannelHandlerContext ctx, Message message) {
    Channel ch = e.getChannel();
    if (message instanceof LoginMessage) {
      authenticate((LoginMessage) message);
      loggedIn = true;
    } else (message instanceof GetDataMessage) {
      if (loggedIn) {
        ch.write(fetchSecret((GetDataMessage) message));
      } else {
        fail();
      }
    }
  }
  ...
}

// Create a new handler instance per channel.
// See ChannelInitializer.initChannel(Channel).
public class DataServerInitializer extends ChannelInitializer<Channel> {
  @Override
  public void initChannel(Channel channel) {
    channel.pipeline().addLast("handler", new DataServerHandler());
  }
}

public interface Message {
  // your methods here
}
@Sharable
public class DataServerHandler extends SimpleChannelInboundHandler<Message> {
  private final AttributeKey<Boolean> auth =
     AttributeKey.valueOf("auth");
  @Override
  protected void messageReceived(ChannelHandlerContext ctx, Message message) {
    Attribute<Boolean> attr = ctx.attr(auth);
    Channel ch = ctx.channel();
    if (message instanceof LoginMessage) {
      authenticate((LoginMessage) o);
      attr.set(true);
    } else (message instanceof GetDataMessage) {
      if (Boolean.TRUE.equals(attr.get())) {
        ch.write(fetchSecret((GetDataMessage) o));
      } else {
        fail();
      }
    }
  }
  ...
}

 public class DataServerInitializer extends ChannelInitializer<Channel> {

   private static final DataServerHandler SHARED = new DataServerHandler();

   @Override
   public void initChannel(Channel channel) {
     channel.pipeline().addLast("handler", SHARED);
   }
 }