ObjectMapper creates list from fields with specific name

Question

I've got a JSON, which I parse to a List of Result objects. This object contains 5 string fields, called photo1, photo2 etc. (based on the JSON) Is it possible to read them directly into a List field?

JSON likes:

{
    "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"
    }]
}

and my object:

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;
    }

I have an 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;
        }

And in the parser:

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

Please add an example json and the object you want to get from it, it's not clear what you're asking. — Oleg, Oct 04 '17 at 10:09
You can do it with `@JsonAnySetter` https://stackoverflow.com/a/30894845/1398418 I don't think there is an easier way. — Oleg, Oct 04 '17 at 11:12

score 2 · Answer 1 · answered Oct 05 '17 at 07:56

Based on Gaetano's answer I wrote a more general solution (any number of photos, any number of other fields

@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;
        }

This is a nice solution. Please pay some attention to the performance . when using reflection the things slow down a lot: https://stackoverflow.com/questions/435553/java-reflection-performance — Gaetano Piazzolla, Oct 05 '17 at 08:14

Gaetano Piazzolla · Answer 2 · 2017-10-04T12:38:14.487

The best solution I've found is to define a Custom Deserializer for your ObjectMapper.

You can tell JACKSON to use the custom deserializer with a specific annotation of the list of "Result" objects on the ApiResponse class:

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;
    }
}

Please pay some attention to the java naming convenction : https://docs.oracle.com/javase/tutorial/java/nutsandbolts/variables.html

The custom deserializer will look like this:

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;
}

score 1 · Answer 3 · answered Oct 05 '17 at 04:53

If you can change your POJO code then the easiest option is to use @JsonAnySetter and @JsonAnyGetter and write custom code there.(Like @Oleg suggested) But don't forget to @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;
    }
}

But if you can't change POJO code you will have to write custom serializer and deserializer

In this way any other attributes will go into the "photos" list, not only the ones named "photos1" "photos2" etc.. — Gaetano Piazzolla, Oct 05 '17 at 08:02
OP's json has no other attributes so it's not a problem. This can be made more robust by checking that `key` starts with `photo` in `setOther`. @Gaetano — Oleg, Oct 05 '17 at 10:36

ObjectMapper creates list from fields with specific name

3 Answers3