Answer by cmsherratt for How to generate a random alpha-numeric string?

If you're happy to use Apache classes, you could use org.apache.commons.text.RandomStringGenerator (commons-text).

Example:

RandomStringGenerator randomStringGenerator =
        new RandomStringGenerator.Builder()
                .withinRange('0', 'z')
                .filteredBy(CharacterPredicates.LETTERS, CharacterPredicates.DIGITS)
                .build();
randomStringGenerator.generate(12); // toUpperCase() if you want

Since commons-lang 3.6, RandomStringUtils is deprecated.