RegularExpressions

Regular expressions are common in many programming languages and Unixish utilities and provide a way to describe the format of text strings. You can write a pattern and then see if a string matches it, or look for all matches, or replace them all with something else, and so on. Here is an example of a regular expression matching typical (but not all) HTTP URLs with optional query strings and fragments:

http://([a-z0-9-]+\.)+[a-z0-9-]+/[^\s#?]*(\?[^\s?#)+?(#[^\s?#)+?

Regex Implementations

J2SE 1.4 supports regular expressions natively in the java.util.regex package. For earlier versions of Java, or for more choices, you can use:

• Apache Jakarta Regexp
• Apache Jakarta ORO
• Gnu Regexp
• JRegex

A comparison of the above libraries is available here http://www.oreilly.com/catalog/regex2/chapter/ch08.pdf

JUnit tests for regexes

• Use regex asserts for testing your application
  • with the sun java 1.4 regex implementation
  • with Jakarta Regexp
  • with the regex implementation you want
• Run test files for the regex implementation
  • Run your own testfiles
  • Run the Jakarta Regexp tests "docs/RETest.txt"
  • Run other implementation tests

Please leave a note on the H&P Open Source Wiki

Also See

Mastering Regular Expressions by Jeffrey Friedl at http://www.oreilly.com/catalog/regex2/ is a good introduction and covers advanced usage, including Java (this chapter is available online).

• Regular Expressions and the Java Programming Language
• Using Regular Expression Groups
• Easy Regex Tutorial

Java Regular Expressions: Taming the java.util.regex Engine by Mehran Habibi at http://www.apress.com/book/bookDisplay.html?bID=177 for complete coverage of the java regex package.

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