public int compare(PartETag tag1, PartETag tag2) {
                    if (tag1.getPartNumber() < tag2.getPartNumber()) return -1;
                    if (tag1.getPartNumber() > tag2.getPartNumber()) return 1;
                    return 0;
                }
Converts the specified list of PartETags to an XML fragment that can be
sent to the CompleteMultipartUpload operation of Amazon S3.

@param partETags
           The list of part ETags containing the data to include in the
           new XML fragment.

@return A byte array containing the data
aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/model/transform/RequestXmlFactory.java