Been running into this as I use Libre office to print out Christmas card address labels.
In every libre office update, the Java Runtime link gets “broken”, causing JRE not found. In Control Panel/Install programs and clicking on Java icon, the update only works to update the 64 bit java install. I noticed that Libre office is a x86 install on a 64 bit Windows OS, and found no Java folder in the C:\Programs x86\ directory. Going to Oracle/java Java SE and installing the JRE-8U102-windows-i586 (in this instance), installing it, then checking under the tools/advanced folder, the x86 is correctly selected. We can now print address labels from a database created in previous Libre office versions. Just sayin’
If you have Win7 Pro 64 bit then it might be better to run the 64 bit version of LibreOffice and also the 64 bit Java.
Exception to this might be if you have some other x86 app that you need to call from within LibreOffice, or if you are calling LibreOffice from within some other x86 application. On windows in general you can only call x86 applications from other x86 applications and x64 applications from other x64 applications.