How to translate "Lorem 3 ipsum dolor sit amet" into SEO friendly "Lorem-3-ipsum-dolor-sit-amet" in Java?

In my blog app, a user can enter any text as a title for their entry and then I generate a URL based on the text.

I validate their title to make sure it only contains letters and numbers.

If they enter something like

Lorem 3 ipsum dolor sit amet

how could I generate the more SEO friendly version of this text:

Lorem-3-ipsum-dolor-sit-amet

It's in practice really not as simple as replacing spaces by hypens. You would often also like to make it all lowercase and normalize/replace diacritics, like á, ö, è and so on which are invalid URL characters. The only valid characters are listed as "Unreserved characters" in the 2nd table of this Wikipedia page.

Here's how such a function can look like:

public static String prettyURL(String string) {
    return Normalizer.normalize(string.toLowerCase(), Form.NFD)
        .replaceAll("\\p{InCombiningDiacriticalMarks}+", "")
        .replaceAll("[^\\p{Alnum}]+", "-");
}

It does basically the following:

• lowercase the string
• remove combining diacritical marks (after the Normalizer has "extracted" them from the actual chars)
• replace non-alphanumeric characters by hyphens

See also:

• JSP 2.0 SEO friendly links encoding

String s = "Lorem 3 ipsum dolor sit amet"
s = s.replaceAll(" ","-");

Since it won't seem to allow me to comment. I would do:

String s = "Lorem 3 ipsum dolor sit amet"
s = s.replaceAll(" ","_");

Using the Underscore character instead because it is a space indicator. Its been a while since I've done java but I know there is a function in .Net that will cleanup a file name so its safe for the file system. I lot of the same general rules applies to a URL so if you can find one in the API it be worth taking a look.