public boolean watch(Path path) {
    path = normalize(path);
    Long modifiedTime;
    try {
      modifiedTime = Files.getLastModifiedTime(path).toMillis();
    } catch (IOException e) {
      modifiedTime = null;
    }
    var last = modificationTimes.put(path, modifiedTime);
    return !Objects.equals(modifiedTime, last);
  }
Adds {@code path} to the set of paths to check on each call to {@link #poll()}.
planetiler-core/src/main/java/com/onthegomap/planetiler/util/FileWatcher.java