java集合lamda常用一些方式

个人最近常使用集合lamda，大致整理下

1. Map的values快速转List
   Map<String,Obj> diagnosisInvoiceMap = new ConcurrentHashMap<>();
   List list = diagnosisInvoiceMap.values().stream().collect(Collectors.toList();

2. 集合的对象某个字段数据转速转Set
   List dataList = new ArrayList();
   Set problemSet = dataList.stream().map(e->e.getFile_id()).collect(Collectors.toSet());

3. 集合数据过滤
   List detaillist = costDetailDtoList.stream().filter(e -> e.getInvoiceNo().equals(hospitalInvoice.getInvoiceNo()) ).collect(Collectors.toList());

4. 判断集合是否过滤到数据(orelse)
   (1)第一种方式
   List dataList = new ArrayList();
   Optional first = dataList ().stream().filter(e -> e.getDrug_name().equals(costDetailDto.getProjectName())).findFirst();
   if(null == first || !first.isPresent()){
   //没有数据
   continue;
   }
   drugListDto = first.get();
   （2）第二种方式
   List dataList = new ArrayList();
   Stream.of(dataList.values()).filter(e -> e.getType().equals(type)).findFirst().orElse(null);
   (3). 第三种方式
   booolean flag = dataList ().stream().anyMach(data->data.equals(“3”)); //另：allMach 意思全部是否等于3，noneMatch正好相反
   为ture为全匹配上

5. 集合数据，转Map:按照集合的某一个属性作为key，把对象作为对象
   (1)方法1
   List dataList = new ArrayList();
   Map<String, Obj> invoiceMap = dataList.collect(Collectors.toMap(paramCalcrate -> paramCalcrate.getInvoiceNo(), Function.identity()));
   （2）方法2
   Map<String, String> attrMap = dataList.stream().collect(Collectors.toMap(Obj::getName, Obj::getCity));
   (3) 方法3
   Map<String, Person> mapByName = persons.stream().collect(Collectors.toMap(Person::getName, p -> p));

6. 集合对象的对象某个字段快速这个字段的集合
   List dataList = new ArrayList();
   List diagCodeList = dataList.map(e->e.getDiagnosisName()).filter(StringUtils::isNotBlank).collect(Collectors.toList());

7. 集合对象的金额属性统计汇总
   List dataList = new ArrayList();
   BigDecimal payAmountSum = dataList.map(AdjustAndPerson::getArealAmount)
   .reduce(BigDecimal.ZERO, BigDecimal::add);
   另：dataList.stream().mapToInt(o -> Objects.isNull(o.getAmount()) ? 0 : o.getAmount()).sum())

8. 集合对象的对象属性字段的以“，”分割
   List dataList = new ArrayList();
   String content = dataList.stream().map(x -> x.getProjectName() + “|” + x.getAmount()).collect(Collectors.joining(“,”));

9. .集合按照集合对象某个属性分组group
   (1) 方法1
   List dataList = new ArrayList();
   Map<String, List> groupBySex = dataList.collect(Collectors.groupingBy(Obj::getItemName));
   (2) 方法2，自定义
   Map<Object, List> cityGroupSelf = dataList .stream()
   .collect(Collectors.groupingBy(obj -> {
   if (“北京”.equals(person.getCity()) || “广州”.equals(person.getCity())) {
   return “北广”;
   } else {
   return person.getCity();
   }
   }));
   });

10. 集合的某个字段排序
    (1)方法1
    List dataList = new ArrayList();
    List result = dataList.values().stream().sorted(
    // 优先1
    Comparator.comparing(GetDuty::getDutyType, Comparator.reverseOrder())
    // 优先2
    .thenComparing(GetDuty::getDutyClass)
    // 优先3
    .thenComparing(GetDuty::getTreatType, Comparator.reverseOrder());
    (2)方法2
    List personsSorted = dataList .stream().sorted((a, b) -> {
    return (int) (a.getBirthday().getTime() - b.getBirthday().getTime());
    }).collect(Collectors.toList());

11. 集合遍历
    List dataList = new ArrayList();
    dataList.forEach(person -> {
    person.setName(person.getName() + “@”);
    });

12. 属性去重
    （1）方法1
    List dataList = new ArrayList();
    List names = dataList.stream().map(p->p.getName()).collect(Collectors.toList());
    System.out.println(“list的属性列表”+names);
    System.out.println(“去重后的列表：”+names.stream().distinct().collect(Collectors.toList()));
    （2）方法2
    TreeSet set = new TreeSet<>(dataList );
    System.out.println(“去重集合:” + set);

13. 集合数据取最大值
    List dataList = new ArrayList(“1”,“2”,“3”);
    int maxValue = dataList.stream().max(Comparator.comparing(Integer,parseInt)).get();

14. 排序
    List result = standardMedicalCatalogDtoList.stream().sorted(
    Comparator.comparing(BStandardMedicalCatalogDto::getCoincidentWordScore, Comparator.reverseOrder())
    .thenComparing(BStandardMedicalCatalogDto::getDrugClassSort)
    .thenComparing(BStandardMedicalCatalogDto::getMedicalCategory)
    ).collect(Collectors.toList());
    转参考资料：https://blog.youkuaiyun.com/qq_31635851/article/details/120322776