class RandomStringUtils {

    public static String random(int length) {
        return new RandomStringGenerator.Builder()
                .filteredBy(NUMBERS, LETTERS)
                .build().generate(length);
    }

}

class RandomStringUtilsTest {

    @SuppressWarnings("unused")
    private final static Logger LOGGER;

    @Test
    public void testRandom() {

        for (int length = 1; length < 10; length++) {
            String value = RandomStringUtils.random(length);
            //LOGGER.debug( "random alphanumeric string: " + value );

            Assert.assertEquals(
                    "random string has a length of " + length,
                    length, value.length());

            Assert.assertTrue(
                    "random string is alphanumeric",
                    isAsciiAlphanumeric(value));
        }
    }

}