Jackson Can not deserialize empty array

Question

Im reading the Facebook Insights and trying to get Jackson to map the JSON to Object. If all the data comes in without empty, i have it working. But Im having a problem trying to deserialize empty array of key value. Even after trying this post: How to prevent null values inside a Map and null fields inside a bean from getting serialized through Jackson it did not resolve the problem :(

This is the JSON :

{"data":[{"id":"492640667465465\/insights\/page_fans_country\/lifetime","name":"page_fans_country","period":"lifetime","values":[{"value":{"MY":26315,"ID":311,"SG":77,"NP":63,"MM":56,"PH":51,"GB":44,"US":44,"KR":36,"TH":36,"IN":34,"BD":24,"PK":22,"BN":22,"AU":15,"TW":14,"VN":12,"KH":11,"YE":11,"CA":10,"JP":10,"EG":8,"ZA":7,"SA":6,"ES":6,"HK":6,"FR":6,"IT":5,"IL":5,"IR":5,"NG":5,"LK":5,"BR":5,"IQ":4,"AF":4,"AE":4,"GT":4,"RO":4,"LR":4,"RU":4,"PS":4,"DE":4,"CN":4,"LY":3,"JO":3},"end_time":"2014-08-02T07:00:00+0000"},{"value":{"MY":26326,"ID":315,"SG":77,"NP":63,"MM":56,"PH":54,"GB":44,"US":43,"TH":38,"KR":36,"IN":33,"BD":23,"BN":22,"PK":21,"AU":16,"TW":14,"VN":12,"KH":11,"YE":11,"CA":10,"JP":10,"EG":8,"ZA":7,"SA":7,"ES":6,"HK":6,"FR":6,"IT":5,"IL":5,"IR":5,"NG":5,"LK":5,"BR":5,"IQ":4,"RU":4,"CN":4,"GT":4,"RO":4,"LR":4,"AF":4,"PS":4,"DE":4,"AE":4,"LY":3,"CH":3},"end_time":"2014-08-03T07:00:00+0000"},{"value":{"MY":26338,"ID":312,"SG":79,"NP":63,"MM":55,"PH":52,"US":45,"GB":44,"TH":39,"KR":34,"IN":32,"BD":24,"BN":22,"PK":21,"AU":16,"TW":14,"KH":12,"VN":12,"CA":11,"YE":11,"JP":10,"EG":8,"ZA":7,"SA":7,"ES":6,"HK":6,"FR":6,"IT":5,"CN":5,"IR":5,"NG":5,"LK":5,"BR":5,"IL":5,"IQ":4,"AF":4,"AE":4,"GT":4,"RO":4,"LR":4,"RU":4,"PS":4,"DE":4,"NZ":3,"TR":3},"end_time":"2014-08-04T07:00:00+0000"}],"title":"Lifetime Likes by Country","description":"Lifetime: Aggregated Facebook location data, sorted by country, about the people who like your Page. (Unique Users)"},{"id":"492640667465465\/insights\/page_storytellers_by_country\/day","name":"page_storytellers_by_country","period":"day","values":[{"value":[],"end_time":"2014-08-02T07:00:00+0000"},{"value":[],"end_time":"2014-08-03T07:00:00+0000"},{"value":[],"end_time":"2014-08-04T07:00:00+0000"}],"title":"Daily Country: People Talking About This","description":"Daily: The number of People Talking About the Page by user country (Unique Users)"},{"id":"492640667465465\/insights\/page_storytellers_by_country\/week","name":"page_storytellers_by_country","period":"week","values":[{"value":{"MY":136,"IN":3,"ID":2,"BD":1,"US":1,"TN":1,"AU":1},"end_time":"2014-08-02T07:00:00+0000"},{"value":{"MY":131,"IN":3,"US":1,"TN":1,"AU":1,"ID":1},"end_time":"2014-08-03T07:00:00+0000"},{"value":{"MY":118,"IN":2,"KH":1,"TR":1,"US":1,"TN":1,"AR":1,"AU":1},"end_time":"2014-08-04T07:00:00+0000"}],"title":"Weekly Country: People Talking About This","description":"Weekly: The number of People Talking About the Page by user country (Unique Users)"},{"id":"492640667465465\/insights\/page_storytellers_by_country\/days_28","name":"page_storytellers_by_country","period":"days_28","values":[{"value":{"MY":492,"IN":5,"ID":3,"AU":2,"SG":2,"ZA":2,"US":2,"GB":2,"RO":1,"PH":1,"NP":1,"BD":1,"JO":1,"PS":1,"TN":1,"IR":1,"CA":1,"CN":1,"KR":1},"end_time":"2014-08-02T07:00:00+0000"},{"value":{"MY":499,"IN":5,"ID":3,"GB":2,"SG":2,"ZA":2,"US":2,"RO":1,"PH":1,"NP":1,"BD":1,"AU":1,"CN":1,"KR":1,"TN":1,"IR":1,"CA":1,"JO":1},"end_time":"2014-08-03T07:00:00+0000"},{"value":{"MY":501,"IN":4,"ID":3,"SG":2,"ZA":2,"US":2,"GB":2,"AU":1,"RO":1,"PH":1,"NP":1,"JO":1,"AR":1,"KR":1,"BD":1,"TR":1,"IR":1,"CA":1,"CN":1,"KH":1,"TN":1},"end_time":"2014-08-04T07:00:00+0000"}],"title":"28 Days Country: People Talking About This","description":"28 Days: The number of People Talking About the Page by user country (Unique Users)"}],"paging":{"previous":"https:\/\/graph.facebook.com\/v2.0\/492640667465465\/insights?since=1406649169&until=1406908369","next":"https:\/\/graph.facebook.com\/v2.0\/492640667465465\/insights?since=1407167569&until=1407426769"}}

My current code does not like this at all --> "value":[]

And the follwing is my Object:

import java.util.Date;
import java.util.List;
import java.util.Map;

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonInclude.Include;

public class Insights {
private Data[] data;
private Paging paging;

public Data[] getData() {
    return data;
}
public void setData(Data[] data) {
    this.data = data;
}
public Paging getPaging() {
    return paging;
}
public void setPaging(Paging paging) {
    this.paging = paging;
}




/**
 * inner class for Data
 * @author pohsoon.yap
 *
 */
public static class Data {
    private String id;
    private String name;
    private String period;
    private Values[] values;
    private String title;
    private String description;

    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getPeriod() {
        return period;
    }
    public void setPeriod(String period) {
        this.period = period;
    }       
    public Values[] getValues() {
        return values;
    }
    public void setValues(Values[] values) {
        this.values = values;
    }
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }


    /**
     * inner class for Values
     * @author pohsoon.yap
     *
     */
    public static class Values {
        // if "value":[]  then this will break
        private Map<String, Integer> Value;
        private String end_time;
        public Map<String, Integer> getValue() {
            return Value;
        }
        public void setValue(Map<String, Integer> value) {
            Value = value;
        }
        public String getEnd_time() {
            return end_time;
        }
        public void setEnd_time(String end_time) {
            this.end_time = end_time;
        }


    }
}

public static class Paging {
    private String previous;
    private String next;

    public String getPrevious() {
        return previous;
    }
    public void setPrevious(String previous) {
        this.previous = previous;
    }
    public String getNext() {
        return next;
    }
    public void setNext(String next) {
        this.next = next;
    }
}
}

My code snippet as follows:

    ObjectMapper mapper = new ObjectMapper();
    mapper.setSerializationInclusion(JsonInclude.Include.NON_EMPTY);
    List<Insights> insightList = new ArrayList();
    String insightStr = "";
    try {

        for (Operation operation : mq.getOperationList()){

            String apiEndPoint = this.facebookGraphApiUrl + operation.getApi();
            apiEndPoint = apiEndPoint.replace("{pageid}", mq.getFacebookPage().getPageId());
            uri = new URI(apiEndPoint);
            insightStr = facebook.getApi().restOperations().getForObject(uri, String.class);

            Insights insights = mapper.readValue(insightStr, Insights.class);

The full stack trace:

com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.LinkedHashMap out of START_ARRAY token at [Source: java.io.StringReader@625a80df; line: 1, column: 1603] (through reference chain: com.social.facebook.model.Insights["data"]->com.social.facebook.model.Data["values"]->com.social.facebook.model.Values["value"]) at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:164) at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:599) at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:593) at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:306) at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:26) at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:375) at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:98) at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:308) at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121) at com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:147) at com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:18) at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:375) at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:98) at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:308) at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121) at com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:147) at com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:18) at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:375) at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:98) at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:308) at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121) at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2796) at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:1942)

The JSON value property seems to be an array type but your model class expects a map. I wonder how the value property looks when it is not empty? — Alexey Gavrilov, Aug 06 '14 at 18:34
@AlexeyGavrilov within the same JSON i attach above, "data" array has 4 items, only one of them has the value as empty, the rest, it looks like this: "value":{"MY":26315,"ID":311} which i thought is a map; a key and a value? — Reusable, Aug 06 '14 at 23:16

score 11 · Answer 1 · answered Sep 11 '16 at 04:20

As explained by others, you are trying to map JSON Array into Java Map, something that is not allowed by default.

But it may be possible to allow empty JSON Array to map to java.util.Map. by enabling DeserializationFeature.ACCEPT_EMPTY_ARRAY_AS_NULL_OBJECT:

objectMapper.enable(DeserializationFeature.ACCEPT_EMPTY_ARRAY_AS_NULL_OBJECT);

this at least works in case of a POJO type; I do not recall if this works for other Java types that usually take JSON Object.

I get `[]` as an empty set from a API (instead of `{}`) and this flag fixed the problem for me. — MrSmith42, May 03 '23 at 14:47

score 6 · Accepted Answer · answered Aug 07 '14 at 07:56

The value field in your model is declared as Map while the corresponding JSON property can be either an empty array or a key-value map. Jackson cannot assign an empty array to a map field.

Assuming that you wish to solve the problem on the client side, you can modify the setValue method to accept a generic Object and then verify whether it is a map or an array (actually List since Jackson deserialize arrays as Java collections). Here is an example:

public class JacksonArrayAsMap {

    public static class Bean {
        private Map<String, Object> value;

        public void setValue(Object value) {
            if (value instanceof Map) {
                this.value = (Map<String, Object>) value;
            } else if (value instanceof List && ((List) value).size() == 0){
                this.value = Collections.EMPTY_MAP;
            } else {
                throw new IllegalArgumentException("Invalid value: " + value);
            }
        }

        @Override
        public String toString() {
            return "Bean{" +
                    "value=" + value +
                    '}';
        }
    }

    public static void main(String[] args) throws IOException {
        final String json1 = "{\"value\":{}}";
        final String json2 = "{\"value\":[]}";
        final String json3 = "{\"value\":{\"a\":\"b\"}}";
        ObjectMapper mapper = new ObjectMapper();
        System.out.println(mapper.readValue(json1, Bean.class));
        System.out.println(mapper.readValue(json2, Bean.class));
        System.out.println(mapper.readValue(json3, Bean.class));
    }
}

Output:

Bean{value={}}
Bean{value={}}
Bean{value={a=b}}

Thanks for the answer, i'll try this out once i wear my hobby hat :) — Reusable, Aug 07 '14 at 14:21
Yay! confirm it works :) i'll continue on other available JSON feed from Graph API. — Reusable, Aug 08 '14 at 02:19

Jackson Can not deserialize empty array

2 Answers2