CODEWITHSUNDEEP
javaregex
gilsilas
gilsilas

Reputation: 1461

How to iterate over regex expression

Let's say I have the following String:

name1=gil;name2=orit;

I want to find all matches of name=value and make sure that the whole string matches the pattern.

So I did the following:

  1. Ensure that the whole pattern matches what I want.

    Pattern p = Pattern.compile("^((\\w+)=(\\w+);)*$");
Matcher m = p.matcher(line);
if (!m.matches()) {
    return false;
}

  2. Iterate over the pattern name=value

    Pattern p = Pattern.compile("(\\w+)=(\\w+);");
Matcher m = p.matcher(line);
while (m.find()) {
    map.put(m.group(1), m.group(2));
}

Is there some way to do this with one regex?

Upvotes: 37

Views: 72436

Answers (3)

Bernhard Barker
Bernhard Barker

Reputation: 55619

You can validate and iterate over matches with one regex by:

  • Ensuring there are no unmatched characters between matches (e.g. name1=x;;name2=y;) by putting a \G at the start of our regex, which mean "the end of the previous match".

  • Checking whether we've reached the end of the string on our last match by comparing the length of our string to Matcher.end(), which returns the offset after the last character matched.

Something like:

String line = "name1=gil;name2=orit;";
Pattern p = Pattern.compile("\\G(\\w+)=(\\w+);");
Matcher m = p.matcher(line);
int lastMatchPos = 0;
while (m.find()) {
   System.out.println(m.group(1));
   System.out.println(m.group(2));
   lastMatchPos = m.end();
}
if (lastMatchPos != line.length())
   System.out.println("Invalid string!");

Live demo.

Upvotes: 43

weaselflink
weaselflink

Reputation: 254

You have to enable multiline-mode for "^" and "$" to work as expected.

Pattern p = Pattern.compile("^(?:(\\w+)=(\\w+);)*$", Pattern.MULTILINE);
while (m.find()) {
    for (int i = 0; i < m.groupCount() - 2; i += 2) {
        map.put(m.group(i + 1), m.group(i + 2));
    }
}

Comments where right, you still have to iterate through matching groups for each line and make the outer group a non-capturing group (?:...).

Upvotes: 4

Mena
Mena

Reputation: 48404

String example = "name1=gil;name2=orit;";
Pattern pattern = Pattern.compile("((name[0-9]+?=(.+?);))+?");
Matcher matcher = pattern.matcher(example);
// verifies full match
if (matcher.matches()) {
    System.out.println("Whole String matched: " + matcher.group());
    // resets matcher
    matcher.reset();
    // iterates over found
    while (matcher.find()) {
        System.out.println("\tFound: " + matcher.group(2));
        System.out.println("\t--> name is: " + matcher.group(3));
    }
}

Output: 

Whole String matched: name1=gil;name2=orit;
    Found: name1=gil;
    --> name is: gil
    Found: name2=orit;
    --> name is: orit

Upvotes: 1

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