stream 分组 分区

分组 Collectors.groupingBy

分区 Collectors.partitioningBy

TestMain.java

package com.nenu;

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

public class TestMain {
    public static void main(String[] args) {
        Student s1 = new Student(1,"test1","111",1);
        Student s2 = new Student(2,"test2","111",1);
        Student s3 = new Student(3,"test3","222",0);
        Student s4 = new Student(4,"test4","333",2);
        Student s5 = new Student(5,"test5","444",0);

        Set<String> stringSet = new HashSet<>();
        stringSet.add("222");
        stringSet.add("333");

        List<Student> studentList = new ArrayList<>();
        studentList.add(s1);
        studentList.add(s2);
        studentList.add(s3);
        studentList.add(s4);
        studentList.add(s5);

        Map<Boolean, List<Student>> collect = studentList.stream().collect(Collectors.partitioningBy(student -> stringSet.contains(student.getCode())));
        Map<Integer, List<Student>> collect1 = studentList.stream().collect(Collectors.groupingBy(Student::getStatus));

        System.out.println("状态0="+collect1.get(0));
        System.out.println("状态1="+collect1.get(1));
        System.out.println("状态2="+collect1.get(2));
        System.out.println("状态true="+collect.get(true));
        System.out.println("状态false="+collect.get(false));


    }
}

结果

状态0=[Student{id=3, code='222', status=0}, Student{id=5, code='444', status=0}]
状态1=[Student{id=1, code='111', status=1}, Student{id=2, code='111', status=1}]
状态2=[Student{id=4, code='333', status=2}]
状态true=[Student{id=3, code='222', status=0}, Student{id=4, code='333', status=2}]
状态false=[Student{id=1, code='111', status=1}, Student{id=2, code='111', status=1}, Student{id=5, code='444', status=0}]

Student.java

package com.nenu;

public class Student {
    private Integer id;
    private String name;
    private String code;
    private Integer status;

    public Student(Integer id, String name, String code,Integer status) {
        this.id = id;
        this.name = name;
        this.code = code;
        this.status = status;
    }

    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 String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public Integer getStatus() {
        return status;
    }

    public void setStatus(Integer status) {
        this.status = status;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", code='" + code + '\'' +
                ", status=" + status +
                '}';
    }
}