regular expression to limit 300 words

Question

I need a regex which success 0-300 words and fails 301 or more words.

I tried:

^\s*(\S+\s+){0,300}\S*$

I also checked

^\W*(?:\w+\b\W*){0,300}$

Both are working fine but in Java I get a java.lang.StackOverflowError. I know using a larger "XSS" I get around this issue but I wanted to ask if there is a way to optimize the regex?

*"Both are working fine but in Java I get a "java.lang.StackOverflowError""* Um, how can they be "working fine" **and** be throwing an exception? — T.J. Crowder, Mar 11 '15 at 08:14
Sorry you're right... Both are doing the job fine if I test the in an online regex tool such as https://regex101.com/ but in Java they are not working — user1635689, Mar 11 '15 at 08:34
Then you'll need to show your code using it, as that's likely to be the problem. — T.J. Crowder, Mar 11 '15 at 08:52

score 2 · Accepted Answer · edited May 23 '17 at 12:06

2

I believe the problem is because the Java implementation of Pattern uses up a stack for each repetition of a group because of backtracking. The solution might be to either change your approach as others have answered or to make all quantifiers possessive :

^\s*(\S+\s+){0,300}+\S*$

or

^\W*(?:\w+\b\W*){0,300}+$

For more info, see here or here.

edited May 23 '17 at 12:06

Community

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answered Mar 11 '15 at 08:43

buftlica

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score 1 · Answer 2 · edited Mar 11 '15 at 09:22

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You can use String.split and check the size of the returned array.

edited Mar 11 '15 at 09:22

CompuChip

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answered Mar 11 '15 at 08:12

Scary Wombat

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I can't, I'm using a constraint framework. And it would really be complicated to write own code (maybe very last resort). Any idea if the regex can be improved? – user1635689 Mar 11 '15 at 08:33
`String.split` is part of standard Java - what do you mean? – Scary Wombat Mar 11 '15 at 08:35
I'm using hibernate constraint, I can't add custom Java code. Only regex changes... – user1635689 Mar 11 '15 at 08:37
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should have maybe mentioned that in your question and tagged it appropriately – Scary Wombat Mar 11 '15 at 08:49

score 0 · Answer 3 · answered Mar 11 '15 at 08:41

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Your regex will fail if the 300th word is the last word and there is notspace ahead of it.You should use

^ *(?:\S+(?: +|$)){0,300} *$

answered Mar 11 '15 at 08:41

vks

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regular expression to limit 300 words

3 Answers3