java8 List去重

一、去除List中重复的String

    public static void main(String[] args) {
        List<String> stringList = new ArrayList<>();
        stringList.add("test1");
        stringList.add("test1");
        stringList.add("test2");
        stringList.add("test2");
        stringList.add("test3");
        stringList = stringList.stream().collect(
                Collectors.collectingAndThen(Collectors.toCollection(
                        () -> new TreeSet<>(Comparator.comparing(String::toString))), ArrayList::new));
        stringList.forEach(System.out::println);
    }

二、按对象属性去重

Object类：

public class Student {
    private String name;

    private int age;

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    @Override
    public String toString() {
        return "Student{" +
            "name='" + name + '\'' +
            ", age=" + age +
            '}';
    }
}

去重测试（通过姓名去重）：



public static void main(String[] args) {
        List<Student> studentList = new ArrayList<>();
        studentList.add(new Student("小明", 12));
        studentList.add(new Student("小明", 12));
        studentList.add(new Student("小华", 13));
        studentList.add(new Student("小华", 13));
        studentList.add(new Student("小王", 15));
        studentList = studentList.stream().collect(
                Collectors.collectingAndThen(Collectors.toCollection(
                        () -> new TreeSet<>(Comparator.comparing(Student::getName))), ArrayList::new));
        studentList.forEach(System.out::println);
    }

三. 对List Map 去重 （对Map中的某个key对应的值进行去重）

public static void main(String[] args) {
    List<Map<String, Object>> mapList = new ArrayList<>();
    Map<String, Object> map1 = new HashMap<>();
    map1.put("id", "val1");
    map1.put("name", "小明");
    Map<String, Object> map2 = new HashMap<>();
    map2.put("id", "val1");
    map2.put("name", "小王");
    Map<String, Object> map3 = new HashMap<>();
    map3.put("id", "val2");
    map3.put("name", "小华");
    Map<String, Object> map4 = new HashMap<>();
    map4.put("id", "val2");
    map4.put("name", "小张");
    Map<String, Object> map5 = new HashMap<>();
    map5.put("id", "val3");
    map5.put("name", "小美");
    mapList.add(map1);
    mapList.add(map2);
    mapList.add(map3);
    mapList.add(map4);
    mapList.add(map5);
    mapList = mapList.stream().collect(
        Collectors.collectingAndThen(Collectors.toCollection(
            () -> new TreeSet<>(Comparator.comparing(m -> (String) m.get("id")))), ArrayList::new));
    mapList.forEach(System.out::println);
}