ObjectMapper 從具有特定名稱的字段創建列表

Question

我有一個 JSON，我將其解析為一個 Result 對象列表。 此對象包含 5 個字符串字段，稱為 photo1、photo2 等（基於 JSON）是否可以將它們直接讀入 List 字段？

JSON 喜歡：

{
    "ErrorMessage": null,
    "Result": [{
        "id": "462290",
        "name_English": "name in english",
        "name_Local": "külföldiül a név",
        "zipcode": "5463",
        "photo1": "dfglkj.com/blabla",
        "photo2": "dfglkj.com/blabla",
        "photo3": "dfglkj.com/blabla",
        "photo4": "dfglkj.com/blabla",
        "photo5": "dfglkj.com/blabla"
    }]
}

和我的對象：

static final class ApiResponse
    {
        public String ErrorMessage;
        public List<Result> Result = new ArrayList<Result>();
    }

 static final class Result
    {
        public String id;
        public String name_English;
        public String name_Local;
        public List<String> photos;
        public String zipcode;
    }

我有一個 ObjectMapper：

private static ObjectMapper newObjectMapper()
        {
            final ObjectMapper om =
                new ObjectMapper()  //
                .configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false)  //
                .configure(JsonParser.Feature.CANONICALIZE_FIELD_NAMES, true);

            om.registerSubtypes(ApiResponse.class);

            return om;
        }

在解析器中：

final ApiResponse ret = OM.readValue(inputStream, ApiResponse.class);

Answer 1

根據 Gaetano 的回答，我寫了一個更通用的解決方案（任意數量的照片，任意數量的其他字段

@Override public List<Result> deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException
        {
            JsonNode node = jp.getCodec().readTree(jp);
            List<Result> listResult = new ArrayList<Result>();

            for (JsonNode interNode : node)
            {
                Result result = new Result();

                for (int i = 1; i < 30; i++)
                {
                    if (interNode.get("photo" + i) != null)
                    {
                        result.photos.add(interNode.get("photo" + i).getTextValue());
                    }
                    else
                    {
                        break;
                    }
                }

                for (Field field : result.getClass().getDeclaredFields())
                {
                    if (interNode.get(field.getName()) != null)
                    {
                        try
                        {
                            field.set(result, interNode.get(field.getName()).getTextValue());
                        }
                        catch (IllegalAccessException e)
                        {
                            e.printStackTrace();
                        }
                    }
                }

                listResult.add(result);
            }

            return listResult;
        }

Answer 2

我發現的最佳解決方案是為您的ObjectMapper定義一個自定義反序列化器。

您可以告訴JACKSON使用帶有 ApiResponse 類上“結果”對象列表的特定注釋的自定義反序列化器：

public class ApiResponse {

    private String errorMessage;

    @JsonDeserialize(using = CustomDeserializer.class)
    private List<Result> result = new ArrayList<Result>();

    public String getErrorMessage() {
        return errorMessage;
    }

    public void setErrorMessage(String arg) {
        errorMessage = arg;
    }

    public List<Result> getResult() {
        if(result==null)
        {
            result = new ArrayList<Result>();
        }
        return result;
    }

    public void setResult(List<Result> arg) {
        result = arg;
    }
}

public class Result {
     private String id;
     private String name_English;
     private String name_Local;
     private List<String> photos;
     private String zipcode;
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getName_English() {
        return name_English;
    }
    public void setName_English(String name_English) {
        this.name_English = name_English;
    }
    public String getName_Local() {
        return name_Local;
    }
    public void setName_Local(String name_Local) {
        this.name_Local = name_Local;
    }
    public List<String> getPhotos() {
        if(photos == null)
        {
            photos = new ArrayList<String>();
        }
        return photos;
    }
    public void setPhotos(List<String> photos) {
        this.photos = photos;
    }
    public String getZipcode() {
        return zipcode;
    }
    public void setZipcode(String zipcode) {
        this.zipcode = zipcode;
    }
}

請注意java命名約定： https ://docs.oracle.com/javase/tutorial/java/nutsandbolts/variables.html

自定義解串器將如下所示：

public class CustomDeserializer extends StdDeserializer<List<Result>> {

private static final long serialVersionUID = -3483096770025118080L;

public CustomDeserializer() {
    this(null);
}

public CustomDeserializer(Class<?> vc) {
    super(vc);
}

@Override
public List<Result> deserialize(JsonParser jp, DeserializationContext ctxt)
        throws IOException, JsonProcessingException {
    JsonNode node = jp.getCodec().readTree(jp);

    List<Result> listResult = new ArrayList<Result>();
    for (JsonNode interNode : node) {

        Result result = new Result();           

        if (interNode.get("id") != null) {
            result.setId(interNode.get("id").asText());
        }
        if (interNode.get("name_English") != null) {
            result.setName_English(interNode.get("name_English").asText());
        }
        if (interNode.get("name_Local")!= null) {
            result.setName_Local(interNode.get("name_Local").asText());
        }
        if (interNode.get("zipcode") !=null ) {
            result.setZipcode(interNode.get("zipcode").asText());
        }

        // photo array
        if (interNode.get("photo1") != null) {
            result.getPhotos().add(interNode.get("photo1").asText());
        }
        if (interNode.get("photo2") != null) {
            result.getPhotos().add(interNode.get("photo2").asText());
        }
        if (interNode.get("photo3") != null) {
            result.getPhotos().add(interNode.get("photo3").asText());
        }
        if (interNode.get("photo4") != null) {
            result.getPhotos().add(interNode.get("photo4").asText());
        }
        if (interNode.get("photo5") != null) {
            result.getPhotos().add(interNode.get("photo5").asText());
        }

        listResult.add(result);
    }

    return listResult;
}

Answer 3

如果您可以更改 POJO 代碼，那么最簡單的選擇是使用@JsonAnySetter和@JsonAnyGetter並在那里編寫自定義代碼。（就像@Oleg建議的那樣）但不要忘記@JsonIgnore List<String> photos 。

@Data // lombok.Data; for getters and setters
public static final class Result {
    public String id;
    public String name_English;
    public String name_Local;
    @JsonIgnore
    public List<String> photos = new ArrayList<>();
    public String zipcode;

    @JsonAnySetter
    public void setOther(String key, String value){
        photos.add(value);
    }
    @JsonAnyGetter
    public Map<String,String> getOther(){
        Map<String,String> map = new HashMap<>();
        for (int i = 0;i<photos.size();i++)
            map.put("photo" + i + 1, photos.get(i));
        return map;
    }
}

但是如果你不能改變 POJO 代碼，你將不得不編寫自定義序列化器和反序列化器