Regular expression example: IP location (ctd)

We now have a total of three expressions to extract the country code from Yahoo and Google referrer strings. To get the country code from a referrer string, we simply try matching the string against each pattern in turn. Since in each case the captured country code will be group 1, we can declare a single Matcher variable, which we successively instantiate with the next pattern on failure. The code looks something like this. Note that we write it in such a way as to avoid calling matches() more than once on the same matcher:

  Pattern pGoogle1 =
  Pattern pGoogle2 = Pattern.compile("(?:http://)?" +
  Pattern pYahoo = Pattern.compile("(?:http://)?" +

  public String guessCountryCode(String referrer) {
    Matcher m = pGoogle1.matcher(referrer);
    if (!m.matches()) {
      m = pGoogle2.matcher(referrer);
      if (!m.matches()) {
        m = pYahoo.matcher(referrer);
        if (!m.matches()) {
          return null;
    String code =;
    if ("UK".equals(code)) {
      code = "GB";
    return code;

Of course if we had a large number of Patterns (as well may happen in real life), we may well want to put them in an array and cycle through in a loop. Notice that at the end of this method we can put in any corrections necessary to turn the domain suffixes and/or language codes into standard country codes (e.g. the standard country code GB generally covers the UK).

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Editorial page content written by Neil Coffey. Copyright © Javamex UK 2021. All rights reserved.