Extracting URLs from a text document using Java + Regular Expressions

Question

I'm trying to create a regular expression to extract URLs from text documents using Java, but thus far I've been unsuccessful. The two cases I'm looking to capture are listed below:

URLs that start with http:// URLs that start with www. (Missing the protocol from the front)

along with the query string parameters.

Thanks! I wish I really knew Regular expressions better.

Cheers,

Answer 1

If you want to make sure you are really matching a url adress and not only some word starting with 'www.' you can use the expression mentioned by DVK before. I modified it slightly and wrote a small code snippet to be a starting point for you:

import java.util.*;
import java.util.regex.*;

class FindUrls
{
    public static List<String> extractUrls(String input) {
        List<String> result = new ArrayList<String>();

        Pattern pattern = Pattern.compile(
            "\\b(((ht|f)tp(s?)\\:\\/\\/|~\\/|\\/)|www.)" + 
            "(\\w+:\\w+@)?(([-\\w]+\\.)+(com|org|net|gov" + 
            "|mil|biz|info|mobi|name|aero|jobs|museum" + 
            "|travel|[a-z]{2}))(:[\\d]{1,5})?" + 
            "(((\\/([-\\w~!$+|.,=]|%[a-f\\d]{2})+)+|\\/)+|\\?|#)?" + 
            "((\\?([-\\w~!$+|.,*:]|%[a-f\\d{2}])+=?" + 
            "([-\\w~!$+|.,*:=]|%[a-f\\d]{2})*)" + 
            "(&(?:[-\\w~!$+|.,*:]|%[a-f\\d{2}])+=?" + 
            "([-\\w~!$+|.,*:=]|%[a-f\\d]{2})*)*)*" + 
            "(#([-\\w~!$+|.,*:=]|%[a-f\\d]{2})*)?\\b");

        Matcher matcher = pattern.matcher(input);
        while (matcher.find()) {
            result.add(matcher.group());
        }

        return result;
    }
}

Answer 2

All RegEx -based code is over-engineered, especially code from the most voted answer, and here is why: it will find only valid URLs! As a sample, it will ignore anything starting with "http://" and having non-ASCII characters inside.

Even more: I have encountered 1-2-seconds processing times (single-threaded, dedicated) with Java RegEx package for very small and simple sentences, nothing specific; possibly bug in Java 6 RegEx...

Simplest/Fastest solution would be to use StringTokenizer to split text into tokens, to remove tokens starting with "http://" etc., and to concatenate tokens into text again.

If you really want to use RegEx with Java, try Automaton