Created a file, It's in memory only, how to save it to disk? Follow

I've got a plugin that creates an xml file and I want that file saved to disk, but I can't seem to find the magic incantation to do so.

This is what I'm doing.

        factory = PsiFileFactory.getInstance(project);

        xmlFile = (XmlFile)factory.createFileFromText("foobar", XMLLanguage.INSTANCE, docToString(doc));
        editorFactory = EditorFactory.getInstance();

        psiDocumentManager = PsiDocumentManager.getInstance(project);
        xmlEditor = editorFactory.createEditor(psiDocumentManager.getDocument(xmlFile));
        FileEditorManager.getInstance(project).openFile(xmlFile.getVirtualFile(), true);
        FileDocumentManager.getInstance().saveAllDocuments();

The xml file opens in an editor tab, but no corresponding file is created on disk.  Ideally I'd like this to be created in a resource directory of the currently open project.