How to get a relative filepath using Java?

Question

Hi,
I'd like to write a custom application for something I'm doing at work. Basically, I need to find the relative filepath from one file to another. Like, if I start in a subdirectory of directory A with file abc.htm, I want to use Java find the relative hyperlink I would put in abc.htm to link to another file in another subdirectory of A. Something like "../Subdirectory/xyz.htm" (where xyz.htm is the file I want to link to) returned as a string.
The reason it needs to be a relative filepath without any references to named directories is that the application with all the hyperlinks in it will eventually reside on a different server or servers. The people who put it there will maintain the same directory structure as we have in our development directory, however.
So, anyway, I see in the File class you have methods for getting absolute filepaths and directory names and such, but nothing for getting a relative link to another file.
Does anyone know if such a class/method exists anywhere in std Java? Or how else I could go about doing this?
Many thanks if you can help.

Answer 1

Given a File object f then one can build the path to the root as a list of file names from f.getName() and iterating using f = f.getParentFile().
Once you have the path lists for your two files then it is simple enough to find the branch point by moving forward through the lists until values differ. Building the relative path is then a matter of moving back through one using "../" until the branch point and then forward through the other until you reach the last element.