Duplicate attribute regex simplification

Question

I am looking for duplicate attributes within the code base, I threw an expression together that works, but I am wondering if it can be made any simpler or more logical.

Sample input

test.append("<td class='no-order' style='text-align:center;' class=\"data text\">");

My attempt

<([^>]*)(class=('|\\")[^('|\\")]+('|\\"))([^>]*)(class=('|\\")[^('|\\")]+('|\\"))([^>]*)>

My thinking was looking for a start tag < then anything that is not an end tag [^>]* followed by a class attribute with either ' or \" and then repeating the whole thing.

As you can see, even though it works, it looks quite long and complicated, is their a simpler way?

Edit:

super bonus brownie points for whoever writes it in the form of a replace all, so it combines the attribute values after running

you could use capturing groups.. check http://docs.oracle.com/javase/tutorial/essential/regex/groups.html — TheLostMind, Apr 30 '14 at 14:11
the thing is a backreference matches _exactly_ the specified match, what if the attributes have different content? `class="hello", class="wow"` — epoch, Apr 30 '14 at 14:13
are you really concerned about "hello" and "wow"?. Both are just names.. You just need class="...." right? — TheLostMind, Apr 30 '14 at 14:15
consider using [jsoup](https://jsoup.org/) instead of regex. There are [many reasons](http://stackoverflow.com/questions/1732348/regex-match-open-tags-except-xhtml-self-contained-tags/1732454#1732454) you should no use regex to parse html. — John Mercier, Apr 25 '17 at 12:59
@JohnMercier, completely missing the point of the question... I have already accepted an answer. this was for a search and replace, not for parsing... — epoch, May 04 '17 at 07:57

Amit Joki · Accepted Answer · 2014-04-30T14:22:56.327

4

You can use the following regex:

<.+(class)=("|').+?\2.+?\1.+>

Escape the regex before you use it.

And if it matches the string, then it contains duplicates. Else, it doesn't.

Explanation:

<.+(class)=("|') matches the < plus any characters till it reaches class= single or double quotes.

The rest of the regex matches the value only if the string contains class again somewhere along the line using backreference.

edited Apr 30 '14 at 14:22

answered Apr 30 '14 at 14:15

Amit Joki

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Very smart, i did not think about _only_ matching for another class attribute, ugh so simple.. accepting – epoch Apr 30 '14 at 14:25
Do you *really* have to create a capture group? ;-) – thefourtheye Apr 30 '14 at 14:26
@epoch, be sure to escape the regex. And I saw the edit. You can't do it with `replaceAll` so easily. You need to do some replace, check if it is equal to original and all sort of things. So, just use `matches` which does it for you ;) – Amit Joki Apr 30 '14 at 14:27
@AmitJoki What will `<.+class=("|').+?\2.+?class.+>` do? – thefourtheye Apr 30 '14 at 14:32
@thefourtheye, it will do the same ;) – Amit Joki Apr 30 '14 at 14:33
@thefourtheye mine is [DRY principle](http://en.wikipedia.org/wiki/Don't_repeat_yourself) `:)` – Amit Joki May 29 '14 at 13:45
Its not working if there are multiple tags in single line like this: `` Can someone please help? – Prabhu Vinod Jan 30 '19 at 10:53

Braj · Answer 2 · 2014-04-30T16:33:18.643

Simply use class=("|') to check for the multiple class attributes.

Sample code:

    String str = "test.append(\"<td class='no-order' style='text-align:center;' class=\"data text\">\");";

    Pattern pattern = Pattern.compile("class=(\"|')");
    Matcher matcher = pattern.matcher(str);
    int index = 0;
    while (matcher.find()) {
        index++;
    }

    if (index > 1) {
        System.out.println("multiple class attribute found");
    }

output:

multiple class attribute found

score 0 · Answer 3 · answered Apr 25 '17 at 12:42

To build on what Amit Joki suggested, if you want to make sure it's in the same element you could use:

<.+(class)=("|').+?\2[^>]+?\1.+>

The addition of [^>] will make sure your second class attribute will reside in the same element as it will match anything except the closing of the tag.

Duplicate attribute regex simplification

3 Answers3