TemporaryFile jar = new TemporaryFile("plugin-classes.jar", null, null);
ZipOutputStream jarStream = new ZipOutputStream(new FileOutputStream(jar.getFile()));
jarStream.setLevel(0);
DirZipper jarZipper = new DirZipper();
jarZipper.addFilePatternToIgnore("^\\..*$");
jarZipper.zipDirectory(javaClassesDir, jarStream);
jarStream.close();
zipper.zipNormalFile(jar.getFile(), zipOutputStream, "files/system/");