code: public InitiateMultipartUploadResponse initiateMultipartUpload(String bucketName, String key) {
          return this.initiateMultipartUpload(new InitiateMultipartUploadRequest(bucketName, key));
      }
docs: Initiates a multipart upload and returns an InitiateMultipartUploadResponse
  which contains an upload ID. This upload ID associates all the parts in
  the specific upload and is used in each of your subsequent uploadPart requests.
  You also include this upload ID in the final request to either complete, or abort the multipart
  upload request.
  
  @param bucketName The name of the Bos bucket containing the object to initiate.
  @param key The key of the object to initiate.
  @return An InitiateMultipartUploadResponse from Bos.