The book Java Regular Expressions: Taming the java.util.regex Engine by Mehran Habibi (published by APress, 2004) is generally regarded as a good study on the topic. If you are interested enough to want to play around with Perl, you can visit the www.perl.com/ website to find tutorials and download a free copy of the software. O'Reilly sponsors the Perl website, and they also support a corresponding “Java in the Enterprise” website at www.onjava.com/. They have some good Java articles and other resources.

See developer.java.sun.com/developer/technicalArticles/releases/1.4regex/ for more information on Java regular expressions.