code: public static Collection<String> listFiles(ClassLoader classLoader, String rootPath) {
      return listResources(classLoader, rootPath, path -> !StringUtils.endsWith(path, "/"));
    }
docs: Finds files within a given directory and its subdirectories
  
  @param classLoader
  @param rootPath    the root directory, for example org/sonar/sqale
  @return a list of relative paths, for example {"org/sonar/sqale/foo/bar.txt}. Never null.