A mechanism is provided for extending a Java archive file to include additional information that describes the contents of the archive as update information. A program is provided for determining differences between an initial file system tree and a final file system tree and encoding those differences into entries in a Java archive file. An extractor class is included in the Java archive file and named as the main class. The Java archive file may be transported to a site that needs a file system update. The Java archive file may be executed in a Java runtime environment to update a target file system. The extractor class is executed to decode and effectuate the difference entries in the archive file.