Luhn Number generator

LuhnGenerator.java

import java.util.Random;

public class LuhnGenerator {
  public static String generate(Integer len) {
    Random rgen = new Random();
    Integer luhnNumber = rgen.nextInt(899999) + 100000;
    String code = luhnNumber.toString();

    return code + generateCheckSum(code);
  }

  public static String generateCheckSum(String code) {
    Integer codeLength = code.length();
    Integer luhnChecksum = 0;
    Integer luhnCheckDigit;
    for (Integer i = codeLength; i > 0; i--) {
      String codeDigit = code.substring(i-1, i);
      Integer luhnDigit = Integer.parseInt(codeDigit);
      if (i % 2 == 0) {
        luhnDigit *= 2;

        if (luhnDigit > 9) {
          luhnDigit -= 9;
        }
      }
      luhnChecksum += luhnDigit;
    }
    luhnCheckDigit = (luhnChecksum * 9) % 10;
    return luhnCheckDigit.toString();
  }
}