code: public CompleteMultipartUploadResponse completeMultipartUpload(String bucketName, String key, String uploadId,
                                                                     List<PartETag> partETags) {
          return this.completeMultipartUpload(new CompleteMultipartUploadRequest(bucketName, key, uploadId, partETags));
      }
docs: Completes a multipart upload by assembling previously uploaded parts.
  
  @param bucketName The name of the bucket containing the multipart upload to complete.
  @param key The key of the multipart upload to complete.
  @param uploadId The ID of the multipart upload to complete.
  @param partETags The list of part numbers and ETags to use when completing the multipart upload.
  @return A CompleteMultipartUploadResponse from Bos containing the ETag for
  the new object composed of the individual parts.