If your application *requires* JDk 1.3.1 (why?), you could consider two Jakarta regular expression packages:
ORO:
http://jakarta.apache.org/oro/index.html and Regexp:
http://jakarta.apache.org/regexp/index.html The usages of them are similar to the JDK 1.4 standard package. However, if you really want to a lot with regular expression, I still recommand JDK 1.4 simply because it provide tighter integrations with a number of
String functions etc.