[移动开发]关于Collections.toMap的坑

首先看下代码

import lombok.AllArgsConstructor;
import lombok.Data;
import org.assertj.core.util.Lists;

import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class TestMap {

    public static void main(String[] args) {
        List<Person> list = Lists.newArrayList();

        list.add(new Person(1, "tom", "北京"));
        list.add(new Person(2, "tom2", "北京1s"));
        list.add(new Person(3, "tom4", null));

        Map<String, String> map = list.stream().collect(Collectors.toMap(Person::getName, Person::getAddress));
        System.out.println(map);
    }

    @Data
    @AllArgsConstructor
    public static class Person {

        private Integer id;
        private String name;
        private String address;


    }


}

看似没有问题，但是执行报错，

?查看源码?才知道?toMap底层调用的map.merge有非空判断

替代方案：

        Map<String, String> map =list.stream().collect(HashMap :: new,(m, v)-> m.put(v.getName(), v.getAddress()), HashMap :: putAll);

?