public class InvertCodeGenerator {public static String generateRandomStr(int len) { String randomcode = ""; String model = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"; char[] m = model.toCharArray(); for (int j = 0; j < 6; j++) { char c = m[(int) (Math.random() * 36)]; // 保证六位随机数之间没有重复的 randomcode = randomcode + c; } return randomcode; }public static void main(String[] args) { LinkedHashSet