There are more robust apps out there that find a Java class given a bunch of jars, but I mostly use this script. Usage is:
jargrep ClassName /scratch/a/dir/with/jars
Script:
#!/bin/bash
# usage: jargrep searchstring dir
for jar in `find $2 -name '*.jar' -type f`
do
echo $jar
jar tvf $jar | grep "$1"
done
I leave the echo of each [...]