code: protected void writeDocumentHeader(XMLEventWriter writer,
                                         String repositoryHash,
                                         Date currentDate)
              throws JournalException {
          try {
              putStartDocument(writer);
              putStartTag(writer, QNAME_TAG_JOURNAL);
              putAttribute(writer, QNAME_ATTR_REPOSITORY_HASH, repositoryHash);
              putAttribute(writer, QNAME_ATTR_TIMESTAMP, JournalHelper
                      .formatDate(currentDate));
          } catch (XMLStreamException e) {
              throw new JournalException(e);
          }
      }
docs: Subclasses should call this method to initialize a new Journal file, if
  they already know the repository hash and the current date.