"Agh for crying out loud, I know that that Java class is in one of these two hundred JARs, just tell me which one!"

Python 3 because that was quickest

findclass.py:

import os, sys, zipfile

top = sys.argv[1]
# e.g. "C:\\Program Files (x86)"

classname = sys.argv[2]
# e.g. "javax.wsdl.factory.WSDLFactory"

member = "/".join(classname.split(".")) + ".class"
# e.g. "javax/wsdl/factory/WSDLFactory.class"

for dirpath, _, filenames in os.walk(top):
	for filename in filenames:
		if not filename.endswith(".jar"):
			continue
		filename = os.path.join(dirpath, filename)

		with zipfile.ZipFile(filename) as jar:
			if member in jar.namelist():
				print(filename)

Usage:

python findclass.py "C:\\Program Files (x86)" javax.wsdl.factory.WSDLFactory