用杰克逊用重复的键转换JSON

问题描述

我正在将json转换为java对象，但是我没有得到想要的东西.我在json中复制了键"friend".

Im converting a json to a java object but I'm not getting what I want.I have duplicated keys "friend" in my json.

我的json:

{
    "id" : "5ee2e2f780bc8e7511a65de9",
    "friends": [{
        "friend": {
            "id": 1,
            "name": "Priscilla Lynch"
        },
        "friend": {
            "id": 2,
            "name": "William Lawrence"
        }
    }]
}

使用ObjectMapper中的readValue只需要最后一个朋友"，但我需要两个.我知道JSONObject使用Map进行转换，所以这就是为什么要使用最后一个.

Using readValue from ObjectMapper only takes the last one "friend" but I need both.I know JSONObject use Map to convert so that's why it is taking the last one.

结果:联系人(id = 5ee2e2f780bc8e7511a65de9，朋友= [{friend = {id = 2，name = William Lawrence}}])

Result:Contacts(id=5ee2e2f780bc8e7511a65de9, friends=[{friend={id=2, name=William Lawrence}}])

ObjectMapper mapper = new ObjectMapper();
Contacts contacts = mapper.readValue(json, Contacts.class);

联系Pojo:

@Getter
@Setter
@ToString
public class Contacts {

    String id;
    List<Object> friends;
}

我想要所有朋友的名单.由于提供json的服务不在我手中，因此我需要找到一种解决方法.我尝试从apache.commons使用MultiMap，但没有成功.我对此卡住了.

I want a list of all friends. As the service whose provide the json is not in my hand I need to find a way to solve it.I tried use MultiMap from apache.commons but no success.Im stuck on this.

推荐答案

当您的JSON Object具有重复的字段时，可以使用com.fasterxml.jackson.annotation.JsonAnySetter批注.结果将为List<List<X>>，因此，您可以使用flatMap方法创建List<X>.参见以下示例:

When you have a JSON Object with duplicated fields you can use com.fasterxml.jackson.annotation.JsonAnySetter annotation. Result will be a List<List<X>> so, you can use flatMap method to create List<X>. See below example:

import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.json.JsonMapper;
import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

import java.io.File;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class DuplicatedFieldsInJsonObjectApp {

    public static void main(String[] args) throws Exception {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        ObjectMapper mapper = JsonMapper.builder().build();
        Contacts contacts = mapper.readValue(jsonFile, Contacts.class);
        System.out.println(contacts.getUnwrappedFriends());
    }
}

@Getter
@Setter
@ToString
class Contacts {

    String id;
    List<Friends> friends;

    public List<Friend> getUnwrappedFriends() {
        return friends.stream().flatMap(f -> f.getFriends().stream()).collect(Collectors.toList());
    }
}

class Friends {

    private List<Friend> friends = new ArrayList<>();

    @JsonAnySetter
    public void setAny(String property, Friend friend) {
        friends.add(friend);
    }

    public List<Friend> getFriends() {
        return friends;
    }
}

@Getter
@Setter
@ToString
class Friend {
    int id;
    String name;
}

上面的代码显示:

[Friend(id=1, name=Priscilla Lynch), Friend(id=2, name=William Lawrence)]

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