//根據(jù)id去重
examRoomModelLists = examRoomModelLists.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(
? ? ? ? ? ? ? ? // 利用 TreeSet 的排序去重構(gòu)造函數(shù)來(lái)達(dá)到去重元素的目的
? ? ? ? ? ? ? ? // 根據(jù)firstName去重
? ? ? ? ? ? ? ? () -> new TreeSet<>(Comparator.comparing(ExamRoomModel::getId))), ArrayList::new));

過(guò)濾StudentExamState=0的數(shù)據(jù)

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

過(guò)濾ExamRoomStudentCount=0的數(shù)據(jù)

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

是不是很方便，換成以前過(guò)濾去重不知道要寫(xiě)多少橫代碼，現(xiàn)在一行解決.

Java8 stream根據(jù)對(duì)象字段去重

public class Java8StreamTest {
    public static class Book{
        private String id;
        private String name;
        public Book(String id, String name) {
            this.id = id;
            this.name = name;
        }
        public String getId() {
            return id;
        }
        public void setId(String id) {
            this.id = id;
        }
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        @Override
        public String toString() {
            return "Book{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                '}';
        }
    }
    @Test
    public void testUnique(){
        List<Book> books = Lists.newArrayList(new Book("1","1"),new Book("2","2"),new Book("3","3"),new Book("2","2"));
		//使用TreeSet去重
        List<Book> unique1 = books.stream().collect(
                collectingAndThen(toCollection(() -> new TreeSet<>(Comparator.comparing(o -> o.getId()))),
                        ArrayList::new));
        System.out.println(unique1);
		//使用map去重
        List<Book> unique2 = books.stream()
                .filter(distinctByKey(o -> o.getId()))
                .collect(Collectors.toList());
        System.out.println(unique2);
    }
    public static <T> Predicate<T> distinctByKey(Function<? super T, Object> keyExtractor) {
        Map<Object, Boolean> seen = new ConcurrentHashMap<>();
        System.out.println("這個(gè)函數(shù)將應(yīng)用到每一個(gè)item");
        return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
    }
}

stream對(duì)list中的對(duì)象進(jìn)行去重

首先我們有一個(gè)對(duì)象屬性如下

@Data
public class Person {
? ? private String id;
? ? private String name;
? ? private String sex;
}

我們根據(jù)屬性name來(lái)去重，去重代碼如下

List<Person> persons = new ArrayList();
//賦值初始化過(guò)程省略
List<Person> uniqueByName = persons.stream().collect(
? ? ? ? ? ? Collectors.collectingAndThen(
? ? ? ? ? ? ? ? ? ? Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(Person::getName))), ArrayList::new)
);

根據(jù)name,sex兩個(gè)屬性去重

List<Person> persons = new ArrayList();
//賦值初始化過(guò)程省略
List<Person> uniqueByNameAndSex = persons.stream().collect(
? ? ? ? ? ?Collectors. collectingAndThen(
? ? ? ? ? ? ? ? ? ? Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(o -> o.getName() + ";" + o.getSex()))), ArrayList::new)
);

以上為個(gè)人經(jīng)驗(yàn)，希望能給大家一個(gè)參考，也希望大家多多支持腳本之家。

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