java8实现List中对象属性的去重方法

java8的stream流能完美解对象集合去重问题.

 List<UserCar> list1 = new ArrayList();
 UserCar userCar = new UserCar();
 userCar.setId(1);
 userCar.setCarNo("AA");
 list1.add(userCar);

 UserCar userCar1 = new UserCar();
 userCar1.setId(2);
 userCar1.setCarNo("AA");
 list1.add(userCar1);


 Person p1 = new Person(1, "11");
 Person p2 = new Person(1, "22");
 Person p3 = new Person(2, "11");
 List<Person> persons = Arrays.asList(p1, p2, p3);

第一种: 不使用java8

 private List<UserCar> removeDupliByRecordId(List<UserCar> userCars) {
 Set<UserCar> personSet = new TreeSet<UserCar>((o1, o2) ->o1.getRecordId().compareTo(o2.getRecordId()));
 personSet.addAll(userCars);

 return new ArrayList<UserCar>(personSet);
 }

 这也是大多数人第一想到的,借助 TreeSet 去重,其中 TreeSet 的其中一个构造函数接收一个排序的算法,同时这也会用到 TreeSet 的去重策略上.

public TreeSet(Comparator<? super E> comparator) {
 this(new TreeMap<>(comparator));
 }

第二种: 炫酷的java8写法

 List<Person> unique = persons.stream().collect(
  Collectors.collectingAndThen(
   Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(Person::getName))), ArrayList::new)
 );
 unique.forEach(p -> System.out.println(p));

第三种: 炫酷的java8写法

 List<String> names = new ArrayList<>();//用来临时存储person的id

 List<Person> personList = persons.stream().filter(// 过滤去重
  v -> {
   boolean flag = !names.contains(v.getName());
   names.add(v.getName());
   return flag;
  }
 ).collect(Collectors.toList());

java8根据某一属性过滤去重

//根据id去重
examRoomModelLists = examRoomModelLists.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(
        // 利用 TreeSet 的排序去重构造函数来达到去重元素的目的
        // 根据firstName去重
        () -> new TreeSet<>(Comparator.comparing(ExamRoomModel::getId))), ArrayList::new));

java8过滤StudentExamState=0的数据

em.setNoLoginExamineeCount((examinee.stream().map(ExamineeEntity::getStudentExamState).filter(x -> 
x == 0).collect(Collectors.toList())).size());
      }

java8过滤ExamRoomStudentCount=0的数据

 List<ExamRoomModel> filterList = examRoomModelLists.stream().filter(ExamRoomModel -> 
 !Objects.equals(ExamRoomModel.getExamRoomStudentCount(), 0)).collect(Collectors.toList());