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

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

		System.out.println(mapp);

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

		Map<Integer, String> 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}