Java regular expression replace issue

Question

public class Main {
    /**
     * @param args
     */
    public static void main(String[] args) {
        String url="http://a.b.com/m/test/index";
        System.out.println(url.replaceAll("^.*?((?<!/)(?:/)(?!/))", ""));
    }
}

The system print is: m/test/index. But in my mind it should print is:/m/test/index. Somebody give some reason?

Use URI/URL class to process them. Don't play around with regular expression in such case. — nhahtdh, Sep 16 '15 at 03:13
While your comment is generally true, a) that's not what the question is about, and b) someone has to write those URL processors. See Asimov's short story "Profession". — Mad Physicist, Sep 16 '15 at 03:17
@MadPhysicist: This is Java. Use the class library. You don't even have to write the class yourself. — nhahtdh, Sep 16 '15 at 03:18
Again, I don't disagree. This question is about regex, not specifically URL. The "http" in the string is incidental. — Mad Physicist, Sep 16 '15 at 03:35
On a side note, is there a reason for using `(?:/)` in the middle instead of just `/`? — Cinnam, Sep 16 '15 at 03:36
@Cinnam In my thinking, no capture group is not replaced which is replaced in fact. — boiledwater, Sep 16 '15 at 03:40
`^.*?((?<!/)(?=/)(?!//))` See [Demo](https://regex101.com/r/oM3vY6/1) — Kerwin, Sep 16 '15 at 03:50
`(?:/)` will matched the `/` before `m`,so we should use `(?=/)` — Kerwin, Sep 16 '15 at 03:51

score 2 · Accepted Answer · answered Sep 16 '15 at 03:15

Your regex reads "As few characters as possible up to and including the first slash that is neither preceded nor followed by a slash". The slash itself is clearly included in the regex. The fact that it is in a non-capturing group does not mean that it is not part of the match.

Java regular expression replace issue

1 Answers1