Jakarta Regexp is a 100% Pure Java Regular Expression package that was graciously donated to the Apache Software Foundation by Jonathan Locke. He originally wrote this software back in 1996 and it has stood up quite well to the test of time. It includes complete Javadoc documentation as well as a simple applet for visual debugging and testing suite for compatibility.
This package is intended to be an answer to a question we commonly hear in the Java world:
"Why isn't there a decent regular expression package available for Java under a BSD-Style (ie: Apache) license?"
If you would like to get involved with this project in one way or another (Mailing lists, SVN, Contributions), please see the Getting Involved section of the Jakarta Website.