protected UploadPartRequest newUploadPartRequest(PartCreationEvent event,
                                                     final File part) {
        final UploadPartRequest reqUploadPart = new UploadPartRequest()
            .withBucketName(req.getBucketName())
            .withFile(part)
            .withKey(req.getKey())
            .withPartNumber(event.getPartNumber())
            .withPartSize(part.length())
            .withLastPart(event.isLastPart())
            .withUploadId(uploadId)
            .withObjectMetadata(req.getUploadPartMetadata())
            .withRequestCredentialsProvider(req.getRequestCredentialsProvider())
            ;
        return reqUploadPart;
    }
Creates and returns an upload-part request corresponding to a ciphertext
file upon a part-creation event.

@param event
           the part-creation event of the ciphertxt file.
@param part
           the created ciphertext file corresponding to the upload-part
aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/UploadObjectObserver.java