title: Send multiple files with S3TransferManager without physical directory
body: <p>Does anyone know how can I send multiple files (as a file list <code>MutableList&lt;File&gt;</code> that I populate within a loop) using the <code>S3TransferManager</code> method <code>uploadDirectory</code> without needing to create the files physically on my disc?
  It does't need to use <code>uploadDirectory</code> method, but I don't want to save them on disc before send them to S3, I have them on memory and I'd like o keep it that way. Here is my code block so far:</p>
  <pre><code>val s3Request = PutObjectRequest.builder()
              .bucket(bucket)
              .key(s3Key)
              .contentType(&quot;application/json; charset=UTF-8&quot;)
              .build()
  val tm = S3TransferManager.create()
  // sending only one file
  val upload = tm.uploadFile { b -&gt; b.source(createFileFromBytes(file)).putObjectRequest(s3Request) }
  upload.completionFuture().join()
  
  ...
  // is there something like (supose my fileMutableList already have all the files I want to send)
  val uploads = tm.uploadFiles { b -&gt; b.source(fileMutableList).putObjectsRequest(s3Request) }
  uploads.completionFuture().join()
  ...
  </code></pre>
  <p>I'm using the <code>software.amazon.awssdk:s3-transfer-manager:2.17.123-PREVIEW</code> lib for Java on my Kotlin project, which you can find out more about it <a href="https://aws.amazon.com/blogs/developer/introducing-amazon-s3-transfer-manager-in-the-aws-sdk-for-java-2-x/" rel="nofollow noreferrer">here</a>.</p>
  <p>Any thoughts are very appreciated.</p>