repository access

Has something changed in the repository API? I used to be able to do:

            Repository repository = Repository.getDefault();
            String fileName = classElement.getName().getFullName().replace('.', '/') + ".java";
            FileObject fileObject = repository.findResource(fileName);
            if (fileObject == null)
            {
                throw new FileStateInvalidException(fileName);
            }

to get the file for a Java object using the name, for example

[-]-, java.lang.String fileName [id: 5272]
    `--- ws/WS.java

but now I get null back, even though there is a package in my project
called "ws" and a file in that package called "WS.java". Is there
another way to search for such a file now? I trying to find the
Project the SourceElement is in, which I evidently can't do without
the file (now thanks to Svata and Tomas at least I know what to do
when I find the file) but I can't find the file in the first place any
more.

Thanks,

Peter