Something You May Not Know about Jar Command: Part 1

1. jar command can also operate on zip files. I usually run jar tvf hello.zip to quickly view its content, without starting up the WinZip program. jar xvf hello.zip should also be able to expand the target zip files. I find it hard to memorize Unix zip/unzip command line options, so I just use jar tvf/jar xvf instead. For example:

C:\tmp > jar tvf eclipse-SDK-3.2RC7-win32.zip

2. jar tvf can selectively list table of contents for archive. I used to run jar tvf j2ee.jar | grep javax/servlet/http to search for servlet classes in j2ee.jar. Replace grep with findstr on Windows. In fact, I don't need grep or findstr; I can just run this command:

jar tvf j2ee.jar javax/servlet/http

Note that the search criteria are matched against the beginning of all entries in jar file. It uses String.startsWith(what) rather than String.contains(what). So this command jar tvf j2ee.jar ejb will not return any matching entries, though jar tvf j2ee.jar javax/ejb will return all ejb classes. The search is also case-sensitive.

If you want case-insensitive search, or match by any parts (not just the beginning) of entries, you still need to use jar tvf my.jar | grep -i aNynAmE

3. You can extract selected entries from a jar file. For instance, if you only want to view the meta-inf/manifest.mf file, you can

C:\Sun\AppServer\lib > jar xvf j2ee.jar META-INF/MANIFEST.MF
inflated: META-INF/MANIFEST.MF

Or using a backslash instead of a forward slash:

C:\Sun\AppServer\lib > jar xvf j2ee.jar META-INF\MANIFEST.MF
inflated: META-INF/MANIFEST.MF

The entry names are case sensitive, and so the following will not extract anything:

C:\Sun\AppServer\lib > jar xvf j2ee.jar meta-inf/manifest.mf

Of course, you can always double-click the entry to view it in WinZip, fileroller, or other tools.

Tags: java, jar, meta-inf, MANIFEST.MF, JDK