code: public static void useNioTransport(NettyChannelBuilder builder) {
      builder.channelType(NioSocketChannel.class);
      builder
          .eventLoopGroupPool(SharedResourcePool.forResource(Utils.NIO_WORKER_EVENT_LOOP_GROUP));
    }
docs: Sets {@link io.grpc.Channel} and {@link io.netty.channel.EventLoopGroup} to Nio. A major
  benefit over using setters is gRPC will manage the life cycle of {@link
  io.netty.channel.EventLoopGroup}.