Stream:常见使用场景

左手的ㄟ右手 2024-03-27 12:24 83阅读 0赞

对Stream流简单使用（单个集合、集合和集合），见[Stream:常用示例][Stream]

此篇博客是对上文未提到的，日常工作中常见的stream用法进行补充

1.  ### 排序 ###

### 1.1 对map排序 ###

//map根据value倒序排序
     map.entrySet().stream().sorted(Collections.reverseOrder(Map.Entry.comparingByValue()));
    //map根据key倒序排序
     map.entrySet().stream().sorted(Collections.reverseOrder(Map.Entry.comparingByKey()));
    //map根据value正序排序
     map.entrySet().stream().sorted(Map.Entry.comparingByValue());
     map.entrySet().stream().sorted(Comparator.comparing(e -> e.getValue())).forEach(System.out::println);
    //map根据key正序排序
     map.entrySet().stream().sorted(Map.Entry.comparingByKey());
     map.entrySet().stream().sorted(Comparator.comparing(e -> e.getKey())).forEach(System.out::println);

#### 1.2 对List<Map>排序 ####

//正序
    List<Map<String,Object> result = list.stream().sorted((m1,m2)-> MapUtils.getIntValue(m1,"totalNum") - MapUtils.getIntValue(m2,"totalNum")).collect(Collectors.toList());
    //或
    List<Map<String, Object>> result = list.stream().sorted(Comparator.comparingInt(m -> MapUtils.getIntValue(m, "totalNum"))).collect(Collectors.toList());
    //倒序
    List<Map<String,Object> result = list.stream().sorted((m1,m2)-> MapUtils.getIntValue(m2,"totalNum") - MapUtils.getIntValue(m1,"totalNum")).collect(Collectors.toList());
    //或
    List<Map<String, Object>> result = list.stream().sorted(Collections.reverseOrder(Comparator.comparingInt(m -> MapUtils.getIntValue(m, "totalNum")))).collect(Collectors.toList());

注意：这里的排序后是重新生成新的集合

1.  ### 去重 ###

### 2.1 按多个属性（字段）去重 ###

List<DeviceManage> collect = dataList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new ConcurrentSkipListSet<>(Comparator.comparing(DeviceManage::getDeviceTypeCode).thenComparing(DeviceManage::getAffiliatedUnitId))), ArrayList::new));

注：

ConcurrentSkipListSet::线程安全

TreeSet::线程不安全

1.  ### 集合合并 ###

List<Integer> mergedList = Stream.of(list1, list2, list3).flatMap(Collection::stream).collect(Collectors.toList());
    
    //List<Object>合并某个属性并转为逗号分隔的字符串
    String opcCodes = dtoList.stream().filter(item -> CollectionUtils.isNotEmpty(item.getFactorSimpleDtoList())).map(PositionFactorsDto::getFactorSimpleDtoList)
            .flatMap(Collection::stream).filter(item2 -> StringUtils.isNotBlank(item2.getOpcCode())).map(FactorSimpleDto::getOpcCode)
            .collect(Collectors.joining(",");

**持续更新......**

[Stream]: https://blog.csdn.net/coder_afly/article/details/128868734