Check if whole text is matched by a part of regex?

Question

Is it possible to check if a text is fully matched by a part of regular expression?

I'd like to match text that is a prefix of (potentially) matching text.

So, for example, I have a following regex:

/etc/tomcat/conf/.*

I'd like to match all files in directory /etc/tomcat/conf/. I can do that by matching full file name against my regex. But I need first to enter that directory, so I'd like to check if I need to enter /etc and /etc/tomcat in first line.

Is it possible to achieve in general case? The regex to match files will come from external system, so it's possible I'd get a regex in form:

/et..tomcat/con.*

If I understand regex machines correctly, it should be possible, because the /et..tomcat/ would be matched agaist /etc/tomcat/, but the match will be negative because the text will and in that moment and the part con.* would not be satisfied. I'd need only to access the internal information, that the text was fully consumed but regex not...

Do Java provides means to check that?

Check the `Matcher`'s documentation: https://docs.oracle.com/javase/8/docs/api/java/util/regex/Matcher.html. The `hitEnd()` method is probably what you are looking for. — Vadim Landa, Sep 06 '17 at 12:04
@VadimLanda thanks, I've made a quick test and it is exactly what I need — 9ilsdx 9rvj 0lo, Sep 06 '17 at 12:16
@LucasTrzesniewski yes, the answer from that question is exactly what I need. The tricky part is, I haven't looked for 'partial mapping' because I'd thought of it only as a case where the whole regex matches a part of the text, not the opposite. — 9ilsdx 9rvj 0lo, Sep 06 '17 at 12:16

score 0 · Answer 1 · answered Sep 06 '17 at 12:09

Only a overcomplex regex. As the idea is to go for single subdirectories, one could do:

Path full = Paths.get("/etc/tomcat/conf");

assert okay(full, Paths.get("/etc")); // -1-
assert !okay(full, Paths.get("/and/so/on")); // -2-

boolean okay(Path full, Path input) {
    try {
        input.relativize(full); // -1- "tomcat/conf"
        return true;
    } catch (IllegalArgumentException e) {
        return false; // -2-
    }
}

Though a bit more code without exception might be worth the effort.

Check if whole text is matched by a part of regex?

1 Answers1