Shorten

private static final int NUM_CHARS_SHORT_LINK = 7;
private static final String ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
private Random random = new Random();
public String generateRandomShortUrl() {
    char[] result = new char[NUM_CHARS_SHORT_LINK];
while (true) {
   for (int i = 0; i < NUM_CHARS_SHORT_LINK; i++) {
        int randomIndex = random.nextInt(ALPHABET.length() - 1);
        result[i] = ALPHABET.charAt(randomIndex);
    }
     String shortLink = new String(result);
      // make sure the short link isn't already used
      if (!DB.checkShortLinkExists(shortLink)) {
            return shortLink;;
        }
    }
}