jdk8对象集合转map集合

package koukay.Controller.Controllers;

import koukay.Portal.webservices.Entity.User;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;

import static java.util.stream.Collectors.toList;

public class A {
    public static void main(String[] args) {
        List<User> list= new ArrayList();
        for (int i = 0; i <5 ; i++) {
            User user = new User();
            user.setCode("code"+i);
            user.setName("name"+i);
            user.setBirthday(new Date());
            list.add(user);
        }
        ObjectMapper objectMapper = new ObjectMapper();
        List<HashMap> collect = list.stream()
                .map(f -> objectMapper.convertValue(f, HashMap.class))
                .collect(toList());
        System.out.println("--------------"+collect.get(0).keySet());
    }
}