Regex not working in class but works in execute anonymous

Question

You can get some context here on my previous post.

When I run the below code on execute anonymous, it renders the following result:

String txt = 'Requesting service for Id Number 9202204720082, Case C - 12246503 and passport A01524783';
String regex = '[ADMT]\\d{8}|\\d{2}[01]\\d[0-3]\\d ?\\d{4} ?[01]8 ?\\d|(?i)C - \\d{8}';
System.debug('========' + regex);
Matcher thematcher = Pattern.compile(regex).matcher(txt);
String idno = (thematcher.find()) ? thematcher.group() : '';
System.debug('========= ' + idno);

When I call the class from execute anonymous:

String txt = 'Requesting service for Id Number 9202204720082';
String regex = '[ADMT]\\d{8}|\\d{2}[01]\\d[0-3]\\d ?\\d{4} ?[01]8 ?\\d|(?i)C - \\d{8}';
System.debug('========' + new EmailLinker(new Messaging.InboundEmail()).findMatch(txt, regex));

If I call the class directly from the backend:

public String findMatch(
    String emailContent,
    String criteriaValue
) {
    String idNumber = '';
    criteriaValue = criteriaValue.unescapeHtml4();
    System.debug('======== Criteria ' + criteriaValue);
    System.debug('======== content ' + emailContent);
    Matcher emailMatcher = Pattern.compile(criteriaValue).matcher(emailContent);
    System.debug('======== email match ' + emailMatcher.find());
    Boolean isFound = Boolean.valueOf(emailMatcher.find());
    //if (isFound == true) {
        System.debug('======== ID ' + emailMatcher.group());
        idNumber = emailMatcher.group();
    //}
    System.debug('======== ID ' + idNumber);
    return idNumber;
}

What am I missing here? Any help is appreciated.

Edit: As per the comment

public String findMatch(
        String emailContent,
        String criteriaValue
    ) {
        String idNumber = '';
        criteriaValue = criteriaValue.unescapeHtml4();
        System.debug('======== Criteria ' + criteriaValue);// [ADMT]\\d{8}|\\d{2}[01]\\d[0-3]\\d ?\\d{4} ?[01]8 ?\\d|(?i)C - \\d{8}
        System.debug('======== content ' + emailContent);
        Matcher emailMatcher = Pattern.compile(criteriaValue).matcher(emailContent);
        if (emailMatcher.find()) {
            System.debug('======== ID ' + emailMatcher.group());
            idNumber = emailMatcher.group();
        }
        System.debug('======== ID ' + idNumber);
        return idNumber;
    }

This is still not working, it only works when I hardcode the regex pattern, and can't do that as it is dynamic.

Answer 1

According to doc

find() Attempts to find the next subsequence of the input sequence that matches the pattern. This method returns true if a subsequence of the input sequence matches this Matcher object's pattern.

hence if you call find() twice, one from Systm.debug another from code., it will try to find next to next sequence, which will fail.

Thus removing Boolean isFound = Boolean.valueOf(emailMatcher.find()); from code should work fine.

I replicated your scenario like this:

public with sharing class EmailLinker {

    public String findMatch(
            String emailContent,
            String criteriaValue) {
        String idNumber = '';
        criteriaValue = criteriaValue.unescapeHtml4();
        System.debug('======== Criteria ' + criteriaValue);
        System.debug('======== content ' + emailContent);
        Matcher emailMatcher = Pattern.compile(criteriaValue).matcher(emailContent);
        System.debug('======== email match ' + emailMatcher.find());

        //if (isFound == true) {
        System.debug('======== ID ' + emailMatcher.group());
        idNumber = emailMatcher.group();
        //}
        System.debug('======== ID ' + idNumber);
        return idNumber;
    }

}

Anonymouos apex :

String txt = 'Requesting service for Id Number 9202204720082';
String regex = '[ADMT]\\d{8}|\\d{2}[01]\\d[0-3]\\d ?\\d{4} ?[01]8 ?\\d|(?i)C - \\d{8}';
System.debug('========' + new EmailLinker().findMatch(txt, regex));

Shows:

16:29:00.168 (179827998)|USER_DEBUG|[8]|DEBUG|======== Criteria [ADMT]\d{8}|\d{2}[01]\d[0-3]\d ?\d{4} ?[01]8 ?\d|(?i)C - \d{8} 16:29:00.168 (179898844)|USER_DEBUG|[9]|DEBUG|======== content Requesting service for Id Number 9202204720082 16:29:00.168 (184007884)|USER_DEBUG|[11]|DEBUG|======== email match true 16:29:00.168 (184074021)|USER_DEBUG|[14]|DEBUG|======== ID 9202204720082 16:29:00.168 (184103751)|USER_DEBUG|[17]|DEBUG|======== ID 9202204720082 16:29:00.168 (184134185)|USER_DEBUG|[3]|DEBUG|========9202204720082

Answer 2

The Apex compiler requires certain characters to be escaped in order to work. This is mentioned in Primitive Data Types:

EscapeSequences: All Strings in Apex use the same escape sequences as SOQL strings: \b (backspace), \t (tab), \n (line feed), \f (form feed), \r (carriage return), " (double quote), ' (single quote), and \ (backslash).

Further, regular expressions also use \ for its own escape sequences.

Subsequently, this means that you need to escape any \ that you want to put into your Apex source code to get them to the regular expression engine.

Pattern p = Pattern.compile('\\bHello\\b');

Matches the full word Hello (\b is the word-border matching pattern in regular expressions).

When your data comes from another place other than Apex source code, you don't need to escape it. This includes reading from a field, a static resource, an email body, and so on. The extra escape sequence is only for Apex source code.