Java Lambda 表达式对集合去重、分组、排序等

た入场券 2024-04-01 13:42 108阅读 0赞

#### 1、排序 ####

List<WorkFlowAuditByVO> auditByListNew = auditByList.stream()
    .sorted(Comparator.comparing(WorkFlowAuditByVO::getStep))
    .collect(Collectors.toList());

// 正序
    List<Ticket> list = tickets.stream().sorted(Comparator.comparing(Ticket::getPlanTime)).collect(Collectors.toList());

// 倒序
    List<Ticket> list = tickets.stream().sorted(Comparator.comparing(Ticket::getPlanTime).reversed()).collect(Collectors.toList());

#### 2、从对象集合中获取属性集合 ####

List<String> userIds = list.stream()
            .map(OntologyMappingTask::getCreatedBy)
            .distinct()
            .map(String::valueOf).collect(Collectors.toList());

#### 3、通过属性对集合分组 ####

Map<String, List<BusinessModelAttribute>> listMap = attrList.stream()
    .collect(Collectors.groupingBy(BusinessModelAttribute::getModelId));

// 对card_id,channel_id,store_id进行分组
    Map<String, List<Map<String, Object>>> glist = counts.stream().collect(Collectors.groupingBy(e -> e.get("card_id").toString()+"#"+e.get("channel_id").toString()+"#"+e.get("store_id")));

#### 4、集合中找出重复的属性值 ####

List<String> repeatEntityArrayList = entityArrayList.stream()
                    .collect(Collectors.groupingBy(a -> a.getName(), Collectors.counting()))
                    .entrySet().stream().filter(entity -> entity.getValue() > 1)
                    .map(entity -> entity.getKey())
                    .collect(Collectors.toList());

#### 转map集合 ####

Map<Long, User> userMap = userList.stream().collect(Collectors.toMap(User::getId, option -> option, (oldOption, newOption) -> newOption));

#### 5、集合去重 ####

// 去重前:[{name=苹果, id=1}, {name=香蕉, id=2}, {name=梨子, id=3}, {name=香蕉, id=4}]
            System.out.println("去重前:" + list);
            ArrayList<Map<String, String>> mapArrayList = list.stream()
                    .collect(Collectors.collectingAndThen(
                            Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(
                                    s -> String.valueOf(s.get("name"))))), ArrayList::new));
     
            // 去重后:[{name=梨子, id=3}, {name=苹果, id=1}, {name=香蕉, id=2}]
            System.out.println("去重后:" + mapArrayList);

// 根据属性name来去重，去重代码如下
    
    List persons = new ArrayList();
    
    //赋值初始化过程省略
    
    List uniqueByName = persons.stream().collect(
    
    Collectors.collectingAndThen(
    
    Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(Person::getName))), ArrayList::new)
    );
    
    // 根据name,sex两个属性去重
    
    List persons = new ArrayList();
    
    // 赋值初始化过程省略
    
    List uniqueByNameAndSex = persons.stream().collect(
    
    Collectors. collectingAndThen(
    
    Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(o -> o.getName() + ";" + o.getSex()))), ArrayList::new)
    
    );

list.stream().distinct().collect(Collectors.toList());