Select ‘Not group’ regular expression

I started this year with a nice regular expression fight.
An expression which I used in an application to select all files which name starts with ‘IWu’ but not ends with ‘Bean’,'Local’ or ‘Home’ followed by ‘.java’ aparently did not work properly.
The expression which I used was:

.*\\IWu.*[^(Bean)|(Home)|(Local)]\.java

Somehow with this expression, filenames like ‘….\IwuRelation.java’ did not validate as true. A small test showed that the group ‘Bean’ in the expression was the cause. Why I don’t know. Maybe because ‘Bean’ and ‘Relation’ share 3 letters; ‘a’,'e’,'n’.

So aparently grouping a combination of letters this way, does not work. What than? It’s easy to create an expression using a group, but how to create one which validates ‘not group’.
After trying many different expressions, I finally found one which seems to do exactly what I wanted it to do. All tests I created were successful for this expression.

.*\\IWu.*(?<!Bean|Home|Local)\.java

This expression uses a negative-lookbehind (”?<!”) function of regular expressions. It looks back and makes sure it does not contain ‘Bean’,'Home’ or ‘Local’. If it does, validation fails.
If you need to define this expression in an XML file, like I did, you have to use CDATA because a ‘<’ is used in the expression.

<![CDATA[.*\\IWu.*(?<!Bean|Home|Local)\.java]]>

This entry was posted on Thursday, January 4th, 2007 at 8:48 pm and is filed under Tools. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.