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javaphpregexreluctant-quantifiersnon-greedy

Java Regexp: UNGREEDY flag

I'd like to port a generic text processing tool, Texy!, from PHP to Java.

This tool does ungreedy matching everywhere, using preg_match_all("/.../U"). So I am looking for a library, which has some UNGREEDY flag.

I know I could use the .*? syntax, but there are really many regular expressions I would have to overwrite, and check them with every updated version.

I've checked

  • ORO - seems to be abandoned
  • Jakarta Regexp - no support
  • java.util.regex - no support

Is there any such library?

Thanks, Ondra

Solution

  • I suggest you create your own modified Java library. Simply copy the java.util.regex source into your own package.

    The Sun JDK 1.6 Pattern.java class offers these default flags:

    static final int GREEDY     = 0;

static final int LAZY       = 1;

static final int POSSESSIVE = 2;

    You'll notice that these flags are only used a couple of times, and it would be trivial to modify. Take the following example:

        case '*':
        ch = next();
        if (ch == '?') {
            next();
            return new Curly(prev, 0, MAX_REPS, LAZY);
        } else if (ch == '+') {
            next();
            return new Curly(prev, 0, MAX_REPS, POSSESSIVE);
        }
        return new Curly(prev, 0, MAX_REPS, GREEDY);

    Simply change the last line to use the 'LAZY' flag instead of the GREEDY flag. Since your wanting a regex library to behave like the PHP one, this might be the best way to go.