Regular Expression using User String

Question

I want to convert an incoming user string into a regular expression, and the incoming string may contain whitespace. Is there a way to ignore all whitespace within the string?

Answer 1

@Zach L and @smas answered your real question

I want to convert an incoming user string into a regular expression ...

I want to warn you to be cautious. It is easy to write a pathological regex that can consume vast amounts of CPU time for certain input strings. If you allow users to enter arbitrary regexes themselves, there is a risk that they will enter a pathological regex, either by accident, or with the intention of overloading your service ...

Answer 2

You may be interested in using the COMMENTS flag in the Pattern class, which:

Permits whitespace and comments in pattern. In this mode, whitespace is ignored, and embedded comments starting with # are ignored until the end of a line.

You can find more info on using flags with Patterns here.

An alternative is to just remove the whitespace before compiling your regex by using either String.replace or String.replaceAll.

Answer 3

Maybe something like this will be good to you:

Pattern p = Pattern.compile("...", Pattern.COMMENTS)

Pattern.COMMENTS means:

Permits whitespace and comments in pattern. In this mode, whitespace is ignored, and embedded comments starting with # are ignored until the end of a line.

Answer 4

Use a regular expression replacement (see http://forums.devx.com/showthread.php?t=145832) to remove the spaces. If you are converting user input to a regular expression, be very careful about escaping (it is like SQL is that users can put in metacharacters that will make your program misbehave); you can get information on proper escaping here.