Groovy loop through Pattern matches

    def regex = 'crt1234[a-z]_(\\w\\w)_DTS(.*)'
    Pattern pattern = Pattern.compile(regex)
    Matcher matcher = pattern.matcher("crt1234_DH_DTS")
    matcher.findAll()

How do I loop through the matches? When I try the following it throws an IllegalStateEx

    for(i in 1..<matcher.count)
    group += matcher.group(i)

I am able to concat the groups using the following code matcher.findAll() { newGroup -> group += newGroup }

Solution

The call to the group method will always fail if there has been no attempt to match the input which is what you are experiencing. Before any calls to the group() method, you need to actually attempt to match. This can be done by calling the find() method on the matcher prior to calling the group() method.

Here is an example found on Geeks for Geeks (modified for your use case):

import java.util.regex.Matcher
import java.util.regex.Pattern

// Get the regex to be checked
String regex = "crt1234[a-z]?_(\\w\\w)_DTS(.*)";

// Create a pattern from regex
Pattern pattern = Pattern.compile(regex);

// Get the String to be matched
String stringToBeMatched = "crt1234_DH_DTS";

// Create a matcher for the input String
Matcher matcher = pattern.matcher(stringToBeMatched);

//find match
matcher.find()

//get matched group at index 1 (0 will be full match, not group)
System.out.println(matcher.group(1)); //outputs: DH

After some more investigation, it seems calling the matcher.count property (groovy enhancement), the groups are cleared and matcher.find() does not result in any more groups. To work around this, you can call matcher.reset() after accessing the matcher.count, then calling matcher.find() works as expected and you can access the matched groups using matcher.group(). Here is an example:

String regex = "crt1234[a-z]?_(\\w\\w)_DTS(.*)";
Pattern pattern = Pattern.compile(regex);
String stringToBeMatched = "crt1234_DH_DTS";
Matcher matcher = pattern.matcher(stringToBeMatched);

//get the count (this will break matcher.group() until matcher.reset() is called
Integer count = matcher.count

//reset the matcher and match the groups
matcher.reset()
matcher.find()

//get matched groups
for(Integer i=0;i<=count;i++){
    System.out.println(matcher.group(i));
}