liquibase-core/src/main/java/liquibase/util/StringUtil.java
public static String randomIdentifer(int len) {
        final String AB = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

        StringBuilder sb = new StringBuilder( len );
        for (int i = 0; i < len; i++)
            sb.append( AB.charAt( rnd.nextInt(AB.length()) ) );
        return sb.toString();
    }
public static String randomIdentifer(int len) {
        final String AB = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

        StringBuilder sb = new StringBuilder( len );
        for (int i = 0; i < len; i++)
            sb.append( AB.charAt( rnd.nextInt(AB.length()) ) );
        return sb.toString();
    }
Produce a random identifer of the given length, consisting only of uppercase letters.
@param len desired length of the string
@return an identifier of the desired length