RegexBugs.java

package javabugs;

import org.junit.Test;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegexBugs {


    protected static String simpleText = "eebbbbcbbbbd";
    protected static Pattern pLazyPossessive = Pattern.compile("^([ebc]*?)(c)?+d$");
    protected static Pattern pLazyGreedy = Pattern.compile("^([ebc]*?)(c)?d$");
    protected static Pattern pGreedyPossessive = Pattern.compile("^([ebc]*)(c)?+d$");

    @Test
    public void testLazyPossesiveSimple() {
        testRegex(pLazyPossessive, simpleText, 1, 2);
    }

    @Test
    public void testLazyGreedySimple() {
        testRegex(pLazyGreedy, simpleText, 1, 2);
    }

    @Test
    public void testGreedyPossessiveSimple() {
        testRegex(pGreedyPossessive, simpleText, 1, 2);
    }


    public void testRegex(Pattern p, String text, int groupA, int groupB) {
        Matcher m = p.matcher(text);
        System.out.append("Text: " + text + "\n\n");
        System.out.append("Pattern: " + p.toString() + "\n");

        if (m.find()) {
            int b = m.start(groupB);
            int a = m.end(groupA);
            System.out.append("Group " + groupB + " starts at " + b + ". Group " + groupA + " ends at " + a + "\n");

            assert b >= a || b < 0 : "There are no group repetitions... How is this happening?";
        }
    }


    /**
     * The real world examples I discovered this with:
     *
     */
    /**
     * group(1) closing slash
     * group(2) tag name
     * group(3) tag attributes
     * group(4) self closing slash
     **/
    protected static Pattern pTag = Pattern.compile("^<(/)?+([\\w\\-\\.:]++)(\\s++[^>]*?)?(/)?+>$");

    /*
     * Doesn't use possessive quantifier "?+"... uses "?"
     */
    protected static Pattern pTag2 = Pattern.compile("^<(/)?+([\\w\\-\\.:]++)(\\s++[^>]*?)?(/)?>$");

    /*
     * Grouping the rest of the regex separately from defective group #4
     */
    protected static Pattern pTag3 = Pattern.compile("^(?:<(/)?+([\\w\\-\\.:]++)(\\s++[^>]*?)?)(/)?+>$");


    protected static String text = "<record class=\"NormalLevel\" fullPath=\"/\" level=\"root\" " +
            "levelDefOrder=\"Year,Tape,Chapter,Section,Normal Level\"  " +
            "levels=\"Year,Tape,Chapter,Section\">";

    @Test
    public void realWorld_testPossesive() {
        testRegex(pTag, text, 3, 4);
    }

    @Test
    public void realWorld_testGreedy() {
        testRegex(pTag2, text, 3, 4);
    }


    @Test
    public void realWorld_testGrouped() {
        testRegex(pTag3, text, 3, 4);
    }


}