According to the LibreOffice Portable support page (https://portableapps.com/support/libreoffice_portable#java), the easiest way to get Java on your portable device is to install Java locally and then use Java Portablizer. Wouldn't installing jPortable (https://portableapps.com/apps/utilities/java_portable) be the easiest solution?
That was copied from an outdated version of OO.o Portable support and is being updated. jPortable is the way to go.
EDIT - I fixed it.
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