拥抱JAVA

String  word = list.stream().map(entity::getxx).collect(Collectors.joining(","));

String date = DateFormatUtils.format(new Date(), "yyyy-MM-dd");

String date2 = "2021-10-01 15:00:00";
Date date = DateUtils.parseDate(date2, "yyyy-MM-dd HH:mm:ss");

LocalDateTime now = LocalDateTime.now();
int year = now.getYear();
int month = now.getMonthValue();
int day = now.getDayOfMonth();

CollectionUtils.isNotEmpty(new ArrayList<>());

Objects.isNull(entity)

List<Object> list1 = Arrays.asList("1", "2", "3", "4");
List<Object> list2 = Arrays.asList("4", "5", "6", "7");
//并集 输出: [1, 2, 3, 4, 5, 6, 7]
CollectionUtils.union(list1, list2);
//交集 输出:[4]
CollectionUtils.intersection(list1, list2);

/**
* 两个时间相差距离多少天多少小时多少分多少秒
*
* @param one
* 时间参数 1 格式：1990-01-01 12:00:00
* @param two
* 时间参数 2 格式：2009-01-01 12:00:00
* @return long[] 返回值为：{天, 时, 分, 秒}
* @throws java.text.ParseException
*/
public static String getDistanceTimes(Date one, Date two) {
    long day = 0;
    long hour = 0;
    long min = 0;
    long time1 = one.getTime();
    long time2 = two.getTime();
    long diff;
    if (time1 > time2) {
        diff = time1 - time2;

        day = diff / (24 * 60 * 60 * 1000);
        hour = (diff / (60 * 60 * 1000) - day * 24);
        min = ((diff / (60 * 1000)) - day * 24 * 60 - hour * 60);
        sec = (diff / 1000 - day * 24 * 60 * 60 - hour * 60 * 60 - min * 60);
    }

    long[] times = { day, hour, min, sec };
    String str = String.format("%d天%d时%d分", day, hour, min);
    return str;
}

//Base64编码
String s = Base64.getEncoder().encodeToString("你好".getBytes(StandardCharsets.UTF_8));
//Base64解码
String s = new String(Base64.getDecoder().decode("你好"), StandardCharsets.UTF_8);

for(User user: userList) {
   for(Role role: roleList) {
      if(user.getRoleId().equals(role.getId())) {
         user.setRoleName(role.getName());
      }
   }
}

Map<Long, List<Role>> roleMap = roleList.stream().collect(Collectors.groupingBy(Role::getId));
for (User user : userList) {
    List<Role> roles = roleMap.get(user.getRoleId());
    if(CollectionUtils.isNotEmpty(roles)) {
        user.setRoleName(roles.get(0).getName());
    }
}

/**
 * 找出两个list的不同元素
 * @param list1
 * @param list2
 * @return
 */
private static List<String> getDiffByHashSet(List<String> list1,List<String> list2){
    //temp存放两个list的共有元素
    List<String> temp = new ArrayList<>();
    //hashSet底层通过hashmpa实现的，为了防止map扩容增加性能代价；初始化长度为两个链表的长度
    Set<String> set = new HashSet<>((int)((float)(list1.size()+list2.size())/0.75F+1.0F));
    for (String s1:list1) {
        set.add(s1);
    }
    for (String s2:list2) {
        //添加不成功说明元素共有
        if(!set.add(s2)){
            temp.add(s2);
        }
        set.add(s2);
    }
    //删除set中存在temp的元素
    set.removeAll(temp);
    return new ArrayList<>(set);
}

//方式一
list.removeIf(item -> "1".equals(item));
//方式二
Iterator it = list.iterator();
while (it.hasNext()){
    User user = (User)it.next();
    if("xxx".equals(user.getxxx())){
        list.remove(user);
    }
}

Map<Integer, Coupon> resultList = couponList.stream().collect(Collectors.groupingBy(Coupon::getCouponId,Collectors.collectingAndThen(Collectors.toList(),value->value.get(0))));

//升序
coDoctorVOList.sort(Comparator.comparing(CoDoctorVO::getTime));
//降序
coDoctorVOList.sort((m1, m2) -> m2.getTime().compareTo(m1.getTime()));

userList = userList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(User::getUserid))), ArrayList::new));