public class UniqueIdUtility {

public static String getSaltString() {

        String SALTCHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";

        StringBuilder salt = new StringBuilder();

        Random rnd = new Random();

        while (salt.length() < 6) { // length of the random string.

            int index = (int) (rnd.nextFloat() * SALTCHARS.length());

            salt.append(SALTCHARS.charAt(index));

        }

        String saltStr = "#"+salt.toString();

        return saltStr;

    }

}

/* Above is the sample method to generate 6 digit Unique String in java */