Can you run java on a NSA310S with entware-ng?

About Java, don't know. Just try it. If the jvm doesn't start, try

LD_LIBRARY_PATH=/opt/lib jvm

where jvm is the name of the binary, to tell the ld loader to use the Entware-ng libraries rather than the firmware ones.

About fw 4.80, I don't think it exists. The point is, the firmware package manager looks for packages in {PACKAGE_ROOT}/{NAS_VERSION}/{FIRMWARE_VERSION}/. MetaRepository can override that, but to install it I can only change {PACKAGE_ROOT} with the web_prefix file. So {NAS_VERSION}/{FIRMWARE_VERSION}/ has to exist, and contain all just MetaRepository. So there is actually only one directory (NSA310/4.40, when I'm not mistaken), with symlinks 4.50, 4.70, … to 4.40, and symlinks NSA320, NSA320, … to NSA310. So to let a '325 with firmware 4.80 install MR, I provide a directory 4.80 for all boxes.

'Installing' is no more than putting the files on the right place. Can't see what is inside the tarball, as I need an Oracle account to download it, but I suppose it contains a bin directory, a lib directory and so on. Put the files in /opt/bin, /opt/lib and so on. Maybe some environment variable is needed to make java able to find it's files. It expects them for instance in /share/java, but that becomes /opt/share/java, because /share/java is not writable or volatile. But I suppose there is a readme in the tarball which tells so.