背景

原因是需要从表里查多个集合list，然后取多个集合得交集，并且元素是对象，所以使用了下面的方式，当然方式有很多种，仅供参考。

案例

下面提供了一段多个集合join取交集的例子，代码中，采用List为集合，Teacher为元素。

package stream;import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;/*** 求多个List<Object>集合的交集** @author happy* @since 2023-06-27*/
public class DistinctEntityByStream {public static void main(String[] args) {getDistinctList();}private static void getDistinctList() {List<Teacher> list = new ArrayList<>();list.add(new Teacher(10, "zhang", 24));list.add(new Teacher(10, "zhang", 24));list.add(new Teacher(10, "zhang", 24));list.add(new Teacher(10, "zhang", 24));list.add(new Teacher(5, "zhang2", 34));list.add(new Teacher(6, "zhang3", 26));list.add(new Teacher(6, "zhang3", 26));list.add(new Teacher(6, "zhang3", 26));list.add(new Teacher(6, "zhang3", 26));list.add(new Teacher(7, "zhang4", 24));list.add(new Teacher(7, "zhang4", 24));List<Teacher> teacherList = list.stream().filter(one -> Collections.frequency(list, one) == 4).filter(distinctByKey(Teacher::getId)).sorted(Comparator.comparing(Teacher::getId)).collect(Collectors.toList());teacherList.forEach(System.out::println);}private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {ConcurrentHashMap<Object, Boolean> seen = new ConcurrentHashMap<>();return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;}public static class Teacher {private Integer id;private String name;private Integer age;public Teacher(Integer id, String name, Integer age) {this.id = id;this.name = name;this.age = age;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;Teacher teacher = (Teacher) o;return Objects.equals(id, teacher.id) && Objects.equals(name, teacher.name) && Objects.equals(age, teacher.age);}@Overridepublic int hashCode() {return Objects.hash(id, name, age);}@Overridepublic String toString() {return "Teacher{" +"id=" + id +", name='" + name + '\'' +", age=" + age +'}';}}}

上面代码在idea中运行结果：

Teacher{id=6, name='zhang3', age=26}
Teacher{id=10, name='zhang', age=24}

代码

代码地址