Conditional Regular Expression in Java?

Question

I have a conditional regular expression that works on regex test websites, such as regexlib.com, but cannot get it to work in my Java application.

But, http://www.regular-expressions.info/conditional.html indicates that Java doesn't support conditionals, but I've seen other posts on SO imply that it does.

An example of my RegEx is: (?(?=^[0-9])(317866?)|[a-zA-Z0-9]{6}(317866?))

It should match either of these inputs: 317866 or 317866A12 or FCF1CS317866

How do I work around this Java limitation?

TIA

Answer 1

Conditional expressions are not supported by java.util.regex.Pattern class. To get around that you could use a 3rd party regexp library such as JRegex

Answer 2

How about just doing this instead?

(?:[a-zA-Z0-9]{6})?(317866?)

Or if you know that the longer version always start with a letter then you can use this:

(?:[a-zA-Z][a-zA-Z0-9]{5})?(317866?)

It will first try to match 6 alphanumerics followed by 31786 or 317866, and if that fails it will then backtrack and try matching 31786 or 317866.