java8两个list集合根据某个字段取交集

可以使用Java 8的Stream API来实现两个List集合根据某个字段取交集。

假设有两个List集合，每个集合都有一个Person对象，其中Person对象有一个id属性，我们需要根据id属性来取交集，可以按照以下步骤操作：

1. 将两个List集合转换成Map，其中Map的key为id，value为Person对象。

Map<Integer, Person> map1 = list1.stream().collect(Collectors.toMap(Person::getId, Function.identity()));
Map<Integer, Person> map2 = list2.stream().collect(Collectors.toMap(Person::getId, Function.identity()));

2. 使用map1的keySet()与map2的keySet()取交集，得到交集的id集合。

Set<Integer> intersection = map1.keySet().stream().filter(map2::containsKey).collect(Collectors.toSet());

3. 根据交集的id集合从map1中获取Person对象集合。

List<Person> result = map1.entrySet().stream().filter(entry -> intersection.contains(entry.getKey())).map(Map.Entry::getValue).collect(Collectors.toList());

完整代码如下：

import java.util.*;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        List<Person> list1 = Arrays.asList(new Person(1, "Tom"), new Person(2, "Jerry"), new Person(3, "Mike"));
        List<Person> list2 = Arrays.asList(new Person(2, "Jerry"), new Person(3, "Mike"), new Person(4, "John"));

        Map<Integer, Person> map1 = list1.stream().collect(Collectors.toMap(Person::getId, Function.identity()));
        Map<Integer, Person> map2 = list2.stream().collect(Collectors.toMap(Person::getId, Function.identity()));

        Set<Integer> intersection = map1.keySet().stream().filter(map2::containsKey).collect(Collectors.toSet());

        List<Person> result = map1.entrySet().stream().filter(entry -> intersection.contains(entry.getKey())).map(Map.Entry::getValue).collect(Collectors.toList());

        System.out.println(result);
    }
}

class Person {
    private int id;
    private String name;

    public Person(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}