Question

I use Java 7.

I would like to extract the lang and the country from a String which represent a bundle file name or properties file name. File name doesn’t contains the extension.

For example

• bundle –> Empty string or null
• bundle_en –> en
• bundle_en_US –> en_US
• complicated_bundle_name_en_US –> en_US

I tried this but it doesn’t give me the expected result.

private static void testPattern(String bundleName) {
        final Pattern pattern = Pattern.compile(".+(_[a-z]{2,3}(_[A-Z]{2,3}){0,1}){0,1}");
        final Matcher matcher = pattern.matcher(bundleName);
        if (matcher.matches()) {
            for (int i = 0; i < matcher.groupCount(); ++i) {
                System.out.println("Group " + i  + " = " + matcher.group(i));
            }
        } else {
            System.out.println("Nothing");
        }
    }

For “bundle_en_US” its show:

Group 0 = bundle_fr_US
Group 1 = null

Can you help me to correct my regex or may be this regex already exist in the java core ?

Thanks.

Answer 1

Problem is imo that .+ in the beginning already matches the whole sequence. Use reluctant quantifier instead:

.+?(_[a-z]{2,3}(_[A-Z]{2,3}){0,1}){0,1}

Edit: The finest solution I would consider this:

.+?(?:_([a-z]{2,3})(?:_([A-Z]{2,3}))?)?

Using non capturing groups this solely captures language and country code and throws out the “_”. Additionally you should change your for condition to i <= matcher.groupCount() otherwise you miss the last group. Using the last version and the altered for condition you get:

Input: bundle
Output:

Group 0 = bundle
Group 1 = null
Group 2 = null

Input: bundle_en
Output:

Group 0 = bundle_en
Group 1 = en
Group 2 = null

Input: bundle_en_US
Output:

Group 0 = bundle_en_US
Group 1 = en
Group 2 = US