Regular Expression not working in Java

Question

I have the string "SELECTOR('(namespace=''ar.com.osde.reintegros'' and eventname=''generacionReintegro'')')".

I need return the string that is between "SELECTOR(" and ")", the result should be: '(namespace=''ar.com.osde.reintegros'' and eventname=''generacionReintegro'')'.

My code with the regular expression is:

public static String extractSelector(String txt){
    Pattern pattern = Pattern.compile("^SELECTOR\\((.*)\\)$");
    Matcher m = pattern.matcher(txt);
    String s = null;
    while (m.find()) {
        s = m.group(1);
    }
    return s;
}

Where txt = "SELECTOR('(namespace=''ar.com.osde.reintegros'' and eventname=''generacionReintegro'')')"

But this always return null. Why is that?

This code looks ok, the problem is probably elsewhere in your code — Reimeus, Jan 22 '15 at 18:20
Could it be that you have a hidden character or a space at the end or the beginning of your string? Try using `txt.trim()` instead of just `txt`. — RealSkeptic, Jan 22 '15 at 18:28
I don't really think this is a duplicate question. At least not a duplicate of the question it's marked as a duplicate of. — Brandon Buck, Jan 22 '15 at 18:55

Willem Van Onsem · Answer 1 · 2015-01-22T18:44:05.430

-1

This jdoodle demonstrates that that part of the code works (only added a declaration for txt and removed the return statement). Are you sure there is nothing done with the txt before that?

Given your code, the only explanation is that txt does not match the pattern fully... This because the while-loop is not executed at all (thus find is always false).

Perhaps there are spaces between SELECTOR and the opening bracket (, perhaps SELECTOR can be put in lowercase. In order to debug this, you can perhaps write

System.out.println("\""+txt+"\"");

Before actually matching it, or use the debugger features of your IDE to do this. The quotes are used to make the spaces more explicit.

edited Jan 22 '15 at 18:44

answered Jan 22 '15 at 18:23

Willem Van Onsem

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This is a comment, not an answer. – Brandon Buck Jan 22 '15 at 18:26
@BrandonBuck: updated it with advice on how to debug. Since it provides ways to fully diagnose the problem, this is more than a comment... – Willem Van Onsem Jan 22 '15 at 18:27
If it doesn't provide a means to resolve the problem (debugging isn't an answer, it's a recommendation) it's still not an answer. – Brandon Buck Jan 22 '15 at 18:29
@BrandonBuck: It does, the only possible reason why this doesn't work is because the while loop isn't executed. That's the only possible explanation because if `txt` was not effective, it would give a `NullPointerException`. The objective of SO is not to resolve problems. It is to share knowledge Q/A-like. That's one of the things people don't tend to pick up. – Willem Van Onsem Jan 22 '15 at 18:35

Regular Expression not working in Java

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