@Override
    public String toString() {
        return MoreObjects.toStringHelper(this)
                          .add("length", length)
                          .add("lastModified", DateFormatter.format(new Date(lastModifiedMillis)))
                          .toString();
    }
Returns the last modified time represented as the number of milliseconds since the epoch.
core/src/main/java/com/linecorp/armeria/server/file/HttpFileAttributes.java