iHotel_student_houtai/src/main/java/com/template/common/utils/StrUtils.java

package com.template.common.utils;

import java.text.ParseException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.UUID;

/**
 * @Author: binguo
 * @Date: 2023/7/25 星期二 14:20
 * @Description: com.repair.common.utils
 * @Version: 1.0
 */
public class StrUtils {

    public static String getRandomName(String fileName){
        int index=fileName.lastIndexOf(".");
        String houzhui=fileName.substring(index);//获取后缀名
        String uuidFileName=UUID.randomUUID().toString().replace("-","")+houzhui;
        return uuidFileName;
    }

    /**
     * 采用URL Base64字符，即把“+/”换成“-_”
     */
    static private char[] alphabet = "01234567899876543210012345678998765432100123456789987654321001234".toCharArray();//"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789xyz".toCharArray();
    /**
     * 获取指定位数的UUID
     * @param bits 指定位数
     * @return
     */

    public static String getUUIDBits(int bits) {
        UUID uuid = UUID.randomUUID();
        long msb = uuid.getMostSignificantBits();
        long lsb = uuid.getLeastSignificantBits();
        char[] out = new char[24];
        int tmp = 0, idx = 0;

        // 循环写法
        int bit = 0, bt1 = 8, bt2 = 8;
        int mask = 0x00, offsetm = 0, offsetl = 0;

        for(; bit < 16; bit += 3, idx += 4) {
            offsetm = 64 - (bit + 3) * 8;
            offsetl = 0;
            tmp = 0;

            if(bt1 > 3) {
                mask = (1 << 8 * 3) - 1;
            } else if(bt1 >= 0) {
                mask = (1 << 8 * bt1) - 1;
                bt2 -= 3 - bt1;
            } else {
                mask = (1 << 8 * ((bt2 > 3) ? 3 : bt2)) - 1;
                bt2 -= 3;
            }
            if(bt1 > 0) {
                bt1 -= 3;
                tmp = (int) ((offsetm < 0) ? msb : (msb >>> offsetm) & mask);
                if(bt1 < 0) {
                    tmp <<= Math.abs(offsetm);
                    mask = (1 << 8 * Math.abs(bt1)) - 1;
                }
            }
            if(offsetm < 0) {
                offsetl = 64 + offsetm;
                tmp |= ((offsetl < 0) ? lsb : (lsb >>> offsetl)) & mask;
            }

            if(bit == 15) {
                out[idx + 3] = alphabet[64];
                out[idx + 2] = alphabet[64];
                tmp <<= 4;
            } else {
                out[idx + 3] = alphabet[tmp & 0x3f];
                tmp >>= 6;
                out[idx + 2] = alphabet[tmp & 0x3f];
                tmp >>= 6;
            }
            out[idx + 1] = alphabet[tmp & 0x3f];
            tmp >>= 6;
            out[idx] = alphabet[tmp & 0x3f];
        }

        return new String(out, 0, bits);
    }

    public static void main(String[] args) throws ParseException
    {
        List<String> data = new ArrayList<>();
        for (int i = 0;i<10000000;i++){
            String sss = getUUIDBits(15);
            data.add(sss);
        }

        long allCount = data.size();
        long disCount = data.stream().distinct().count();

        Collections.sort(data);
        String sss ="";

    }
}