urlregex.java

import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeSet;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Main {
	
	static final String protocol = "(?<protocol>(?:https?:\\/\\/?)+(?:www(?!.))?)?";
	static final String tdl = "(?<tdl>[a-zA-Z0-9@:._-]{2,256}\\.[a-z0-9]{2,6}(?:[:0-9]{1,5})?)";
	static final String path = "(?<path>(?:\\/)[-a-zA-Z0-9\\/_]+)?";
	static final String params = "(?<params>[-a-zA-Z0-9?%#+()=&]+)?";
	
	static Map<Integer, String> namedGroups = new HashMap<>();

	public static void main(String[] args) throws Exception {
		Set<String> set = new TreeSet<>();
		set.add("http://foo.com/blah_blah");
		set.add("http://foo.com/blah_blah/");
		set.add("https://www.example.com/wpstyle/?p=364");
		set.add("https://www.example.com/wpstyle/wpath/?p=364&?param=this");
		set.add("https://www.example.com/foo/?bar=baz&inga=42&quux");
		set.add("google.com");
		set.add("www.google.com");
		set.add("http://foo.com:");
		set.add("http://foo.com:8080/blah_blah");
		set.add("https://www.example.com/foo/?bar=baz&inga=42&quux");
		
        int matchCount = 0;
        
		for (String element : set) {
            matchCount = matchCount + 1;
			runRegex(element, matchCount);
		}
	}

	private static void runRegex(String string, int matchCount) {
        Pattern p = Pattern.compile(protocol + tdl + path + params);
        
        setNamedGroupCandidates(p.toString());
        
        Matcher m = p.matcher(string);


        if (m.find()) {
            // Remove invalid groups
            Iterator<String> i = namedGroups.values().iterator();
            while (i.hasNext()) {
                try {
                    m.group(i.next());
                } catch (IllegalArgumentException e) {
                    i.remove();
                }
            }

            System.out.println("Match " + matchCount + ":");
            System.out.println();
            printMatches(m, namedGroups.values());
        }
	}

    private static void printMatches(Matcher matcher, Collection<String> namedGroups) {
        for (String name: namedGroups) {
            String matchedString = matcher.group(name);
            if (matchedString != null) {
                System.out.println(name + ": " + matchedString);
            }
        }
        System.out.println();
        System.out.println("------------------------");
    }

	private static void setNamedGroupCandidates(String regex) {
		Matcher m = Pattern.compile("\\(\\?<([a-zA-Z][a-zA-Z0-9]*)>").matcher(regex);
		int order = 0;
		while (m.find()) {
			order += 1;
			namedGroups.put(order, m.group(1));
		}
	}
}