java - 使用 Jackson 反序列化时如何映射重复命名的字段？

Question

我有一个简单的 Java 类，如下所示:

public class AllAdverts {

    @JsonIgnoreProperties(value="id", ignoreUnknown=true)
    public static class Advert {

        @JsonProperty(value="_id")
        public String advertId;

        public String adgroupId;
    }

    public List<Advert> adverts;

    public AllAdverts(String json) throws IOException {
        this.adverts = MyUtils.mapper.readValue(json, 
                new TypeReference<List<Advert>>(){});
    }
}

我正在尝试反序列化以下 JSON:

[
    {
        "_id": "535788abf789b8916a8b456e",
        "adgroup_id": "535788abf789b8916a8b456c",
        "subcampaign_id": "535788abf789b8916a8b4569",
        "id": 6005879321807,
    },
    {
        "_id": "535788abf789b8916a8b456f",
        "adgroup_id": "535788abf789b8916a8b456c",
        "subcampaign_id": "535788abf789b8916a8b4569",
        "id": 6005879319007,
    }
]

当我将 JSON 传递到类 AllAdverts 的构造函数中时，除了名为 advertId 的字段之外，JSON 都会正确映射。

正如您所看到的，JSON 有两个名为 id 和 _id 的字段，我认为 Jackson 将这两个字段视为 id，因此，我无法加载这个。我该如何解决这个问题？我一直在深入研究文档，并认为 JsonProperty 注释可以解决这个问题，但它没有起作用。虽然 adgroupId 有值，但 advertId 为 null。

Answer 1

您的映射器是否使用/删除下划线并将大写字母替换为小写字母来填充 bean 属性？因为这似乎就是正在发生的事情。如果没有，Jackson 就不会填写 adgroupId 字段。

检查您的映射器。

下面是我的代码，完全没有问题(意识到我必须注释 adgroupId 字段，因为 json 和 pojo 字段之间的名称差异:

Main.java

import java.util.List;

import org.json.JSONArray;
import org.json.JSONObject;

import com.fasterxml.jackson.databind.ObjectMapper;

public class Main {

    public static void main(String[] args) throws Exception {
        new Main().start();
    }

    public List<Advert> adverts;

    private void start() throws Exception {

        String jsonString =
                "[" +
                    "{" +
                        "\"_id\": \"535788abf789b8916a8b456e\"," +
                        "\"adgroup_id\": \"535788abf789b8916a8b456c\"," +
                        "\"subcampaign_id\": \"535788abf789b8916a8b4569\"," +
                        "\"id\": 6005879321807," +
                    "}," +
                    "{" +
                        "\"_id\": \"535788abf789b8916a8b456f\"," +
                        "\"adgroup_id\": \"535788abf789b8916a8b456c\"," +
                        "\"subcampaign_id\": \"535788abf789b8916a8b4569\"," +
                        "\"id\": 6005879319007," +
                    "}" +
                "]";

        ObjectMapper mapper = new ObjectMapper();

        JSONArray jsonArray = new JSONArray(jsonString);
        for (int i = 0; i < jsonArray.length(); i++) {
            JSONObject jsonObject = jsonArray.getJSONObject(i);

            Advert advert = mapper.readValue(jsonObject.toString(), Advert.class);

            System.out.println("advertId: " + advert.advertId);
            System.out.println("adgroupId: " + advert.adgroupId);
        }

    }

}

Advert.java

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;

@JsonIgnoreProperties(value = "id", ignoreUnknown = true)
public class Advert {

    public Advert() {}

    @JsonProperty(value = "_id")
    public String advertId;

    @JsonProperty(value = "adgroup_id")
    public String adgroupId;

}

我正在使用 Jackson 2.4.1。