Java regex to extract text between tags

Question

I have a file with some custom tags and I'd like to write a regular expression to extract the string between the tags. For example if my tag is:

[customtag]String I want to extract[/customtag]

How would I write a regular expression to extract only the string between the tags. This code seems like a step in the right direction:

Pattern p = Pattern.compile("[customtag](.+?)[/customtag]");
Matcher m = p.matcher("[customtag]String I want to extract[/customtag]");

Not sure what to do next. Any ideas? Thanks.

For starters, you need to escape the [] square brackets which are metacharacters in a regex. — ridgerunner
– ridgerunner, Commented Jul 3, 2011 at 2:28

Wiktor Stribiżew · Accepted Answer · 2018-11-21 21:23:21Z

199

You're on the right track. Now you just need to extract the desired group, as follows:

final Pattern pattern = Pattern.compile("<tag>(.+?)</tag>", Pattern.DOTALL);
final Matcher matcher = pattern.matcher("<tag>String I want to extract</tag>");
matcher.find();
System.out.println(matcher.group(1)); // Prints String I want to extract

If you want to extract multiple hits, try this:

public static void main(String[] args) {
    final String str = "<tag>apple</tag><b>hello</b><tag>orange</tag><tag>pear</tag>";
    System.out.println(Arrays.toString(getTagValues(str).toArray())); // Prints [apple, orange, pear]
}

private static final Pattern TAG_REGEX = Pattern.compile("<tag>(.+?)</tag>", Pattern.DOTALL);

private static List<String> getTagValues(final String str) {
    final List<String> tagValues = new ArrayList<String>();
    final Matcher matcher = TAG_REGEX.matcher(str);
    while (matcher.find()) {
        tagValues.add(matcher.group(1));
    }
    return tagValues;
}

However, I agree that regular expressions are not the best answer here. I'd use XPath to find elements I'm interested in. See The Java XPath API for more info.

edited Nov 21, 2018 at 21:23

Wiktor Stribiżew

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answered Jul 3, 2011 at 2:06

hoipolloi

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3 Comments

b10hazard Over a year ago

Thanks so much, that is just what I needed. I will look into XPaths, but for now I think this solution will work. My applications is very simple and will probably stay that way. Thanks again!

K.Sopheak Over a year ago

What about this string "<tag>apple</tag><b>hello</b><tag>orange</tag><tag>pear"? How can we get pear without close tag?

TroniPM Over a year ago

To generalize: private String extractDataFromTags(String tag) { Pattern pattern = Pattern.compile("<.+?>(.+?)</.+?>"); Matcher matcher = pattern.matcher(tag); matcher.find(); return (matcher.group(1)); // Prints String I want to extract or throws exception }

jdc0589 · Accepted Answer · 2011-07-03 17:59:48Z

17

To be quite honest, regular expressions are not the best idea for this type of parsing. The regular expression you posted will probably work great for simple cases, but if things get more complex you are going to have huge problems (same reason why you cant reliably parse HTML with regular expressions). I know you probably don't want to hear this, I know I didn't when I asked the same type of questions, but string parsing became WAY more reliable for me after I stopped trying to use regular expressions for everything.

jTopas is an AWESOME tokenizer that makes it quite easy to write parsers by hand (I STRONGLY suggest jtopas over the standard java scanner/etc.. libraries). If you want to see jtopas in action, here are some parsers I wrote using jTopas to parse this type of file

If you are parsing XML files, you should be using an xml parser library. Dont do it youself unless you are just doing it for fun, there are plently of proven options out there

edited Jul 3, 2011 at 17:59

answered Jul 3, 2011 at 2:10

jdc0589

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1 Comment

b10hazard Over a year ago

Thanks for the suggestion. I've bookmarked them and I will certainly look into using this in future projects. For now the regex method is probably the one I will go with since the file I'm parsing is very small/simple.

Gorky · Accepted Answer · 2019-06-13 11:03:58Z

8

A generic,simpler and a bit primitive approach to find tag, attribute and value

    Pattern pattern = Pattern.compile("<(\\w+)( +.+)*>((.*))</\\1>");
    System.out.println(pattern.matcher("<asd> TEST</asd>").find());
    System.out.println(pattern.matcher("<asd TEST</asd>").find());
    System.out.println(pattern.matcher("<asd attr='3'> TEST</asd>").find());
    System.out.println(pattern.matcher("<asd> <x>TEST<x>asd>").find());
    System.out.println("-------");
    Matcher matcher = pattern.matcher("<as x> TEST</as>");
    if (matcher.find()) {
        for (int i = 0; i <= matcher.groupCount(); i++) {
            System.out.println(i + ":" + matcher.group(i));
        }
    }

edited Jun 13, 2019 at 11:03

answered Sep 3, 2015 at 0:49

Gorky

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2 Comments

kapishreshth Over a year ago

What would be the pattern If there is a sequence of different tags or nested tags like <h2>Mac</h2><h1>loves it</h1> or <h2>Mac<h1>liked your answer</h1></h2>?

AVA Over a year ago

please edit i < matcher.groupCount(); to i <= matcher.groupCount(); to include first matching substring ie. at 0th index

Shubham Khurana · Accepted Answer · 2017-07-24 14:38:45Z

5

    String s = "<B><G>Test</G></B><C>Test1</C>";

    String pattern ="\\<(.+)\\>([^\\<\\>]+)\\<\\/\\1\\>";

       int count = 0;

        Pattern p = Pattern.compile(pattern);
        Matcher m =  p.matcher(s);
        while(m.find())
        {
            System.out.println(m.group(2));
            count++;
        }

answered Jul 24, 2017 at 14:38

Shubham Khurana

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Comments

Gopal00005 · Accepted Answer · 2017-12-04 11:24:53Z

4

Try this:

Pattern p = Pattern.compile(?<=\\<(any_tag)\\>)(\\s*.*\\s*)(?=\\<\\/(any_tag)\\>);
Matcher m = p.matcher(anyString);

For example:

String str = "<TR> <TD>1Q Ene</TD> <TD>3.08%</TD> </TR>";
Pattern p = Pattern.compile("(?<=\\<TD\\>)(\\s*.*\\s*)(?=\\<\\/TD\\>)");
Matcher m = p.matcher(str);
while(m.find()){
   Log.e("Regex"," Regex result: " + m.group())       
}

Output:

10 Ene

3.08%

edited Dec 4, 2017 at 11:24

Gopal00005

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answered Oct 23, 2015 at 20:12

Heriberto Rivera

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Comments

Bibhuti Agarwal · Accepted Answer · 2013-12-04 12:03:33Z

2

    final Pattern pattern = Pattern.compile("tag\\](.+?)\\[/tag");
    final Matcher matcher = pattern.matcher("[tag]String I want to extract[/tag]");
    matcher.find();
    System.out.println(matcher.group(1));

answered Dec 4, 2013 at 12:03

Bibhuti Agarwal

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1 Comment

user1514499 Over a year ago

how about prefix for tag (if prefix is dynamic)

Shirik · Accepted Answer · 2011-07-03 02:06:41Z

1

I prefix this reply with "you shouldn't use a regular expression to parse XML -- it's only going to result in edge cases that don't work right, and a forever-increasing-in-complexity regex while you try to fix it."

That being said, you need to proceed by matching the string and grabbing the group you want:

if (m.matches())
{
   String result = m.group(1);
   // do something with result
}

answered Jul 3, 2011 at 2:06

Shirik

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Comments

Marryam Shahzad · Accepted Answer · 2022-05-26 16:01:18Z

0

This works for me, use in your main method below Scanner input. Works for Hackerrank "Tag Content Extractor" also.

  boolean matchFound = false;
        Pattern r = Pattern.compile("<(.+)>([^<]+)</\\1>");
        Matcher m = r.matcher(line);

        while (m.find()) {
            System.out.println(m.group(2));
            matchFound = true;
        }
        if ( ! matchFound) {
            System.out.println("None");
        }
        
        testCases--;

answered May 26, 2022 at 16:01

Marryam Shahzad

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