code: public NettyServerBuilder keepAliveTime(long keepAliveTime, TimeUnit timeUnit) {
      checkArgument(keepAliveTime > 0L, "keepalive time must be positive");
      keepAliveTimeInNanos = timeUnit.toNanos(keepAliveTime);
      keepAliveTimeInNanos = KeepAliveManager.clampKeepAliveTimeInNanos(keepAliveTimeInNanos);
      if (keepAliveTimeInNanos >= AS_LARGE_AS_INFINITE) {
        // Bump keepalive time to infinite. This disables keep alive.
        keepAliveTimeInNanos = SERVER_KEEPALIVE_TIME_NANOS_DISABLED;
      }
      if (keepAliveTimeInNanos < MIN_KEEPALIVE_TIME_NANO) {
        // Bump keepalive time.
        keepAliveTimeInNanos = MIN_KEEPALIVE_TIME_NANO;
      }
      return this;
    }
docs: Sets a custom keepalive time, the delay time for sending next keepalive ping. An unreasonably
  small value might be increased, and {@code Long.MAX_VALUE} nano seconds or an unreasonably
  large value will disable keepalive.
  
  @since 1.3.0