There is a tiny little utility that let's you inspect JAR/WAR/EAR files on the Mac OS platform. The software is available here. Install it. To open a JAR, simply right click and chose JarInspector as the application. I personally did not set JarInspector as my default .jar application to let the default JAR launcher kicks in but I have been very close to.
Amongst the useful features:
- navigate in your jars recursively
- edit/view files (useful for MANIFEST.MF)
- decompile a class
- find a file/class by name
By the way, this utility also opens zip files.