[Java知识库]集合分组：Collectors.groupingBy()

数据库中有groupby 分组，Java里面其实也有的，感觉很好用。对List里面的数据进行分组，一行代码解决问题，太爽了

话不多说，上代码。

people实体：按照人员的地址分组，使用map<key,List<people>>接收。

public class People {
    private Integer id;
    private String name;
    private String address;
    private Integer 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 String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public People() {
    }

    public People(Integer id, String name, String address, Integer age) {
        this.id = id;
        this.name = name;
        this.address = address;
        this.age = age;
    }

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

实例方法：

public class Test {
    public static void main(String[] args) {
        People people1=new People(1,"only-qi1","11",11);
        People people2=new People(2,"only-qi2","12",12);
        People people3=new People(3,"only-qi3","14",13);
        People people4=new People(1,"only-qi4","14",14);
        People people5=new People(2,"only-qi5","13",15);
        People people6=new People(1,"only-qi6","11",16);
        ArrayList<People>arrayList=new ArrayList<>();
        arrayList.add(people1);
        arrayList.add(people2);
        arrayList.add(people3);
        arrayList.add(people4);
        arrayList.add(people5);
        arrayList.add(people6);
        Map<String,List<People>>map=arrayList.stream().collect(Collectors.groupingBy(People::getAddress));
        for (String s : map.keySet()) {
            System.out.println("key值是："+s+"========="+"value的值是"+map.get(s));
        }
    }
}

执行结果：