I wrote a program to do this for myself using the JarFile class, but I
doubt it is general or robust enough to be useful to anyone else.
JarBrowser on SourceForge looks like it will do the trick:

http://jarbrowser.sourceforge.net/

There's also a commercial utility (trial version available) that looks
like it will search most kinds of archive files, including jars. (I am
not associated with ZipScan in any way and know nothing about their
product, just found it by googling.)

http://www.zipscan.co.uk/

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I have a student project writeup at
http://mindprod.com/projects/which.html

If you have any budget, I would be happy to write such a tool for you.

You didn't say what OS you're using, but I'd use a shell script.
Something like:

for f in *.jar
do
    echo "Jar file is $f"
    jar t $f | grep classname
done

where 'classname' is the name of the class you're looking for. As a
bonus you'll also be told the package name as well. That works for any
*nix system.

You could do essentially the same in Java by using the JarFile, Manifest
and Pattern classes. Use JarFile to pull the Manifest out of each jar
file and Pattern to search the output stream you can get from the Manifest.

Dang,
I've only been toying with Java for a couple of months and that's one
of the first things I did.  And you guys are trying to get him to buy
something. :-(

The "entries" method of "java.util.zip.ZipFile" works on jar files as
well as zip files it will return an enumeration - "size" will tell you
how many files are in the jar.

Lee