基于jdk8的常用编程api

这里记录的全部是自己平时开发的项目中所用到的方法或者技巧，其中有的可以完全使用 Hutool 工具包替代

一、基于jdk8的常用编程api

1. list数据返回前端过滤字段方法

// list数据返回前端过滤字段方法
List<ZlDataStandard> queryList = zlDataStandardService.findList(new ZlDataStandard());
List<Dict> dictList = queryList.stream().collect(ArrayList::new, (list, item) -> {
   Dict dict = Dict.create()
         .set("id", item.getId())
         .set("standardName", item.getStandardName())
         .set("standardDescribe", item.getStandardDescribe())
         .set("standardCode", item.getStandardCode())
         .set("standardType", item.getStandardType());
   list.add(dict);
}, ArrayList::addAll);
// 查询栏目
CmsContent content = cmsContentService.getById(id);
Dict dict = Dict.create().parseBean(content)
    // 过滤出bean中的属性id", "title", "subtitle", "image 其他的字段一概不要
    .filter("id", "title", "subtitle", "image")
    .set("type", column.getType());

2. java 8 stream 使用sorted排序

List<Dict> collect = list.stream().sorted(Comparator.comparing(ZlEvaluate::getCreateTime, Comparator.reverseOrder())).collect(ArrayList::new, (arrList, item) -> {
    Dict dict = Dict.create()
            .set("id", item.getId())
            .set("modelId", item.getModelId())
            .set("evaluateNum", item.getEvaluateNum());
    arrList.add(dict);
}, ArrayList::addAll);

3. 对于list集合使用java8中新特性排序，按照指定字段排序

List<ZlDataGovernResult> zlDataGovernResultList = list.stream().sorted(Comparator.comparing(ZlDataGovernResult::getPassRate)
     .thenComparing(ZlDataGovernResult::getPassRate,Comparator.reverseOrder())).limit(5).collect(Collectors.toList());

4. 集合 list 转 map

Map<Integer, Apple> appleMap = appleList.stream().collect(Collectors.toMap(Apple::getId, a -> a,(k1,k2)->k1));


public List<PersonVO> selectPersons(List<Long> personIds) {
    List<PersonVO> persons = new ArrayList<>(personIds.size());
    List<Person> personList = personMapper.selectByIds(personIds);
    //批量查询，转换成Map
    List<PersonExt> personExtList = personExtMapper.selectByIds(person.getId());
    Map<String, PersonExt> personExtMap = personExtList.stream().collect(Collectors.toMap(PersonExt::getPersonId, Function.identity()));
    for (Person person : personList) {
        PersonVO vo = new PersonVO();
        //直接从Map中查找
        PersonExt personExt = personExtMap.get(person.getId());
        // 组装数据
        persons.add(vo);
    }
    return persons;
}

5. 属性拷贝

// 属性拷贝
BeanUtils.copyProperties(Object source, Object target);

6. 集合中常见操作

// 集合判空
CollectionUtils.isEmpty(details)

// 集合排序
Collections.sort(list,Comparator.comparing(Rule::getPriority).thenComparing(Rule::getPriority).reversed());

// 随机排序
Collections.shuffle(list);

// 集合循环
List<String> list = new ArrayList<>();
coupons.forEach(n -> {
        list.add(n.getId());
});
parents.forEach((p) -> {
    this.add(o);
});

// 集合分组
Map<Integer, List<Apple>> groupBy = appleList.stream().collect(Collectors.groupingBy(Apple::getId));

// 集合 list 转 map
Map<Integer, Apple> appleMap = appleList.stream().collect(Collectors.toMap(Apple::getId, a -> a,(k1,k2)->k1));

// 集合去重
List list=(List) a.stream().distinct().collect(Collectors.toList());

// 集合取属性
List<String> courseIds=  users.stream().map(UserEntity::getUserName).collect(Collectors.toList());

// 集合过滤
list.stream().filter(user-> user.getId() > 5 && "1组".equals(user.group)).collect(Collectors.toList());

// 集合取部分
List newList = list.subList(start, end);

// 集合类型转换
Integer[] aftIdArray = (Integer[]) ConvertUtils.convert(questionIds, Integer.class);

// 时间转换
LocalDateTime midnight = LocalDateTime
                        .now()
                        .plusDays(1)
                        .withHour(0)
                        .withMinute(0)
                        .withSecond(0)
                        .withNano(0);
                long seconds = ChronoUnit.SECONDS.between(LocalDateTime.now(), midnight);

7. 异步执行

TimerUtil.instance().addTaskSeconds((timeout) -> {
        // TODO 异步执行方法
}, 2);

8. 字符串和list互相转换

// 字符串转list
List<String> payTypes = Arrays.asList(payTypeStr.split(CommonConstants.SIGN_COMMA));
// list转字符串
String s = org.apache.commons.lang.StringUtils.join(list.toArray(), ",");

9. java stream 流的发方式分页加排序

// java  stream 流的发方式分页加排序
    List<DiScript> collect = scriptList.stream().skip(pageSize * (pageNum - 1)).limit(pageSize).sorted(
                Comparator.comparing(DiScript::getCreateDate)).collect(Collectors.toList());

10. 格式化数字

// 格式化数字
public static void main(String[] args) {
    System.out.println(String.format("%03d", 1));
    // 输出001
}