jdk 8新特性 List.stream() .distinct() 去重 List中对象多条件去重

一；去重

public static Predicate distinctByKey(Function super T, ?> keyExtractor) {
Map seen = new ConcurrentHashMap<>();
return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
}

distinct()不对对象列表进行去重的直接实现。它是hashCode()和equals()工作的
用Stream接口的 filter()接收为参数

List lists = list.stream().filter(distinctByKey(user->user.getUid())).collect(Collectors.toList());

二；去重

对象中的部分元素的重复

//long num = addList.stream().distinct().count();
long count = addList.stream().collect(Collectors.collectingAndThen(
                Collectors.toCollection(() -> new TreeSet<>(
                        Comparator.comparing(po ->DateTimeFormatter.ofPattern("yyyy-MM-dd").format(po.getOrderTime()) + ";" + po.getCityCode()))), ArrayList::new)).stream().count();
        Assert.checkBoolean(addList.size() == count, "Excel中,存在相同日期的城市活跃度");

DateTimeFormatter.ofPattern(“yyyy-MM-dd”).format(po.getOrderTime()):
是LocalDateTime 类型格式化
正常这样写：Comparator.comparing(p->p.getOrderTime() + “;” + p.getCityCode()))), ArrayList::new)

三、stream 遍历List<Map<String,Object>> key 获取值放到List中

 List<Map<String,Object>> listMap=new ArrayList<>();
        Map<String,Object> ma1=new HashMap<>();
        ma1.put("code",123456);
        Map<String,Object> ma2=new HashMap<>();
        ma2.put("code",456);
        listMap.add(ma1);
        listMap.add(ma2);
        List<String> collect = listMap.stream()
                .flatMap(map -> map.entrySet().stream())
                .filter(entry -> "code".equals(entry.getKey()))
                .map(Map.Entry::getValue)
                .map(Object::toString)
                .collect(Collectors.toList());
        System.out.println("33");
        System.out.println(collect);//[123456, 456]