How to use

HttpRequest$BodyPublisher

in

java.net.http

private static long accumulateLen(List<BodyPublisher> publishers) {
  int len = 0;
  for (var publisher : publishers) {
    if (publisher.contentLength() < 0) {
      return -1;
    }
    len += publisher.contentLength();
  }
  return len;
}

  @Override
  public void onComplete() {
    synchronized (AggregateSubscription.this) {
      index++;
      if (index == publishers.length) {
        subscriber.onComplete();
      } else {
        var bodyPublisher = publishers[index];
        bodyPublisher.subscribe(this);
        if (requestCount > 0) {
          currentSubscription.request(requestCount);
          requestCount = 0;
        }
      }
    }
  }
}

private AggregateSubscription(BodyPublisher[] publishers, Subscriber<? super ByteBuffer> subscriber) {
  this.publishers = publishers;
  this.subscriber = subscriber;
  this.subscriberAdapter = this.new SubscriberAdapter();
  publishers[0].subscribe(subscriberAdapter);
}