stream 里面的 Collectors.toMap 用法 ; list转map

https://blog.csdn.net/jiangpingjiangping/article/details/76474010

第一步：

package test;

public class Person {

    private Integer id;
    private String name;

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



}

第二步：

package test;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Test {
    public static void main(String[] args) {

        List list = new ArrayList();
        list.add(new Person(1, "haha"));
        list.add(new Person(2, "rere"));
        list.add(new Person(3, "fefe"));



        Map mapp = list.stream().collect(Collectors.toMap(Person::getId, Function.identity()));

        System.out.println(mapp);

        System.out.println(mapp.get(1).getName());

        Map map = list.stream().collect(Collectors.toMap(Person::getId, Person::getName));

        System.out.println(map);

    }

}

得到的结果：

{1=test.Person@4b9385, 2=test.Person@1311334, 3=test.Person@2a0b20}

haha

{1=haha, 2=rere, 3=fefe}