Can converted @PathVariables reference each other?
@RequestMapping("/admin/{dept}/{mod}/")
public String showModule(@PathVariable String dept, @PathVariable String mod) {
    Department department = dao.findDepartment(dept);
    Module module = department.findModule(mod);
    return "view";
}

@RequestMapping("/admin/{dept}/")
public String showDept(@PathVariable Department dept) {
    return "view";
}

@RequestMapping("/admin/{deptAndModule}/")
public String showDept(@PathVariable DepartmentAndModule deptAndModule) {
    return "view";
}