Java Regex Engine Crashing

Question

Regex Pattern - ([^=](\\s*[\\w-.]*)*$)

Test String - paginationInput.entriesPerPage=5

Java Regex Engine Crashing / Taking Ages (> 2mins) finding a match. This is not the case for the following test inputs:

paginationInput=5

paginationInput.entries=5

My requirement is to get hold of the String on the right-hand side of = and replace it with something. The above pattern is doing it fine except for the input mentioned above.

I want to understand why the error and how can I optimize the Regex for my requirement so as to avoid other peculiar cases.

regex seems overkill, have you thought about using testString.split("=") on each line of this file and checking that length ==2? That will return an array and the second item will be the right side of the = — Daniel Rucci
– Daniel Rucci, Commented Dec 2, 2010 at 5:01
That's the crude way to do it. I'm leaving it as my last resort. — kaychaks
– kaychaks, Commented Dec 2, 2010 at 5:10
There's too much backtracking allowed in your regex so you're probably getting stack overflows if it doesn't match quickly. Try to avoid nesting *s, or see if you can make them possessive - you want to help it fail faster. — CurtainDog
– CurtainDog, Commented Dec 2, 2010 at 5:17

Nicole · Accepted Answer · 2010-12-02 05:58:45Z

1

You can use a look behind to make sure your string starts at the character after the =:

(?<=\\=)([\\s\\w\\-.]*)$

As for why it is crashing, it's the second * around the group. I'm not sure why you need that, since that sounds like you are asking for :

A single character, anything but equals
Then 0 or more repeats of the following group:
- Any amount of white space
- Then any amount of word characters, dash, or dot
End of string

Anyway, take out that *, and it doesn't spin forever anymore, but I'd still go for the more specific regex using the look behind.

Also, I don't know how you are using this, but why did you have the $ in there? Then you can only match the last one in the string (if you have more than one). It seems like you'd be better off with a look-ahead to the new line or the end: (?=\\n|$)

[Edit]: Update per comment below.

edited Dec 2, 2010 at 5:58

answered Dec 2, 2010 at 5:06

Nicole

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8 Comments

kaychaks Over a year ago

your pattern does not give me the RHS of "=" in the string "something.operer= asda adad" as it has space in between words. My second * was to take care of these instances. And I will have only one match per string hence I could use "$"

Nicole Over a year ago

Ah, well if spaces are allowed on the right side, simply move the \\s into the character class instead of adding another *. You only need repeating groups if the pattern is more strict than that. Updated my answer too.

kaychaks Over a year ago

I already did that, was about to update here. Thanks anyway for the help.

tchrist Over a year ago

That equals does not need to be escaped. Also, this pattern only works for ASCII.

Nicole Over a year ago

@tchrist The equals doesn't need to be escaped? What kind of feedback is that? Who cares? It has a functional equals sign immediately preceding it, so I escaped it A) to be safe, B) to be less confusing. So since I'm obviously not the expert here, maybe you can tell me what the negatives are?

|

Jim Garrison · Accepted Answer · 2010-12-02 05:03:31Z

0

Try this:

=\\s*(.*)$

answered Dec 2, 2010 at 5:03

Jim Garrison

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