@Override
  public String getExtension() {
    int pos = path.lastIndexOf('.');
    if (pos == -1) {
      return null;
    }

    String extension = path.substring(pos + 1);
    if (StringUtils.isEmpty(extension)) {
      return null;
    }
    return extension;
  }
The class used to represent the resource in the class path.
src/main/java/com/eudemon/ratelimiter/env/io/ClassPathResource.java