自定义简单的规则（可以末尾或者开头添加时间戳（加密））完美。

package demo.day.web;

import java.util.Random;

/**
 * @description: demo
 * @author: nice
 * @created: 2022/06/17 08:58
 */
public class demo2 {
    private final static Integer num = 9;
    private final static Integer numSum = 60;
    /**
     * 设置规则字符串
     * */
    private String setCode(String code,String number){
        int start = num / 2;
        int end = num - start - 1;
        StringBuffer stringBuffer = new StringBuffer(code);
        // 取前3个字符放第4位开始
        stringBuffer.replace(3,start - 1,number.substring(0,start));
        // 取后3个字符放末尾倒数第4位开始
        StringBuffer stringBufferOne = new StringBuffer(stringBuffer.toString());
        stringBufferOne.replace(stringBufferOne.length() - end - 1 ,stringBufferOne.length() - 3 ,number.substring(end));
        return stringBufferOne.toString();
    }
    /**
     * 验证规则字符串
     * */
    private boolean isCheck(String code){
        int start = num / 2;
        int end = num - start;
        String num = code.substring(3,start + 3);
        num += code.substring(code.length() - ( 3 + end),code.length() - 3);
        int sum = 0;
        for (int i = 0 ; i < num.length() ; i++){
            sum += getInt(num.substring(i,i+1));
        }
        return sum == numSum;
    }
    private int getInt(String str){
        try{
            return Integer.parseInt(str);
        }catch (Exception e){
            return 0;
        }
    }
    /**
     *  生成规则字符串
     * */
    private String getStringEncryption(int encryptionNumber){
        if(encryptionNumber > 32 || encryptionNumber < 16){
            throw new RuntimeException(" 只能填写16~32之间数字 ");
        }
        // 生成一个32位随机串
        String code = getString(encryptionNumber);
        // 生成6位数字且相加等于24
        String number = getRandomNumber(num,numSum);
        // 设置规则
        String codeNew = setCode(code,number);
        return codeNew;
    }
    /**
     * 获取随机数和等于sum
     * */
    private String getRandomNumber(int num,int sum){
        // 随机数 * 9 不能小于等于 sum
        if(num <= 0 || num * 9 <= sum){
            return null;
        }
        String str = "";
        int yj = 0;  // 预警总额(计算前)
        int yjh = 0;  // 预警总额(计算后)
        int yjsy = sum;  // 预警总额(剩余额度)
        for(int i = 0 ; i < num ; i++){
            Integer random = getRandom();
            if(yjsy > 9 * (num - i - 1)){
                if(yjsy - 9 > 0){
                    str += "9";
                    yjh += 9;
                    yjsy -= 9;
                    yj += 9;
                    continue;
                }
                str += yjsy;
                continue;
            }
            yj += random;
            if(yj <= sum){
                str += random;
            }else if(yjh >= sum){
                str += "0";
            }else if(yjh <= sum){
                str += (sum - yjh);
            }
            yjh += random;
            yjsy -= random;
        }
        return str;
    }
    /**
     * 获取随机数 [0-9]
     * */
    private Integer getRandom(){
        Random r = new Random();
        return r.nextInt(10);
    }
    /**
     * 获取随机字符串（字母与数字）
     * */
    private String getString(int n) {
        Random r = new Random();
        String code = "";//分配一个空字符内存
        for(int i = 0; i < n; i++) {
            int type = r.nextInt(3);
            switch(type) {
                case 0://大写字母
                    char c0 = (char)(r.nextInt(26) + 65);//ASII中大写字母的范围
                    code += c0;
                    break;
                case 1 ://小写字母
                    char c1 = (char)(r.nextInt(26) + 97);//ASII中小写字母的范围
                    code += c1;
                    break;
                case 2://数字
                    int m = r.nextInt(10);//生成0~9的随机数
                    code += m;
                    break;
            }
        }
        return code;
    }

    public static void main(String[] args) {
        demo2 s = new demo2();
        String code = s.getStringEncryption(32);
        System.out.println("输出加密的code = " + code);
        boolean isTrue = s.isCheck(code);
        System.out.println("验证加密的code = " + isTrue);
    }
}