is it true ?

example.java

public class WebSocketMessageHandler extends SimpleChannelInboundHandler<WebSocketFrame> {

    private static final Logger LOGGER = LoggerFactory.getLogger(WebSocketMessageHandler.class);

    private static final ChannelGroup allChannels = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, WebSocketFrame frame) throws Exception {
        if (frame instanceof TextWebSocketFrame) {
            final String text = ((TextWebSocketFrame) frame).text();
            LOGGER.info("Received text frame {}", text);
            allChannels.stream()
                       .filter(c -> c != ctx.channel())
                       .forEach(c -> {
                           frame.retain();
                           c.writeAndFlush(frame.duplicate());
                       });
        } else {
            throw new UnsupportedOperationException("Invalid websocket frame received");
        }
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        LOGGER.info("Adding new channel {} to list of channels", ctx.channel().remoteAddress());
        allChannels.add(ctx.channel());
    }
}