Hello,
No other class of phpdocx uses Java but the conversion plugin based on OpenOffice.. The conversion plugin based on LibreOffice doesn't need Java (using the newest packages of LibreOffice, not an old one).
Please follow the installation page and the debug page to get the source of the problem:
https://www.phpdocx.com/documentation/conversion-plugin/conversion-plugin-installation-and-set-up
https://www.phpdocx.com/documentation/conversion-plugin/debugging-libreoffice
https://www.phpdocx.com/documentation/conversion-plugin/common-problems-and-possible-errors
Regards.