List s3 keys recursively

ListKeys.scala

import scala.collection.JavaConverters._

val request = new ListObjectsV2Request()
request.setBucketName(bucket)
request.setPrefix(prefix)

@tailrec
def fetch(req: ListObjectsV2Request, xs: Iterable[String]): Iterable[String] = {
  val result = s3Client.listObjectsV2(req)
  val keys   = xs ++ result.getObjectSummaries.asScala.map(_.getKey)

  if (result.isTruncated) {
    req.setContinuationToken(result.getNextContinuationToken)
    fetch(req, keys)
  } else keys
}

Source(fetch(request, Iterable.empty[String]).toList)