ACCEPT_EMPTY_STRING_AS_NULL_OBJECT with List field

Question

with Jackson, I'm trying to properly deserialize a JSON which contains empty string as no value values. Herein an example:

{
  "code" : "REQ500",
  "description" : "Problem with Service",
  "params" : ""
}

and the bean I would get:

public final class MyError {

    @JsonProperty("code")
    private String code;

    @JsonProperty("description")
    private String description;

    @JsonProperty("params")
    private List<String> params;

    // [CUT]

    public void setParams(List<String> params) {
        this.params = params;
    }
}

Using ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, I've create an object mapper with

public static final ObjectMapper OBJECT_MAPPER = new ObjectMapper()
    .configure(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, true)
    .registerModule(new SimpleModule().addDeserializer(LocalDate.class, new DateDeserializer()));

expecting to have params = null, but deserialization doesn't work. Herein the error I got:

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot 
deserialize instance of `java.util.ArrayList` out of VALUE_STRING token
 at [Source: (String)"{
  "code" : "REQ500",
  "description" : "Problem with Service",
  "params" : ""
}"; line: 4, column: 14] (through reference chain: solutions.infinitec.fabrick.models.common.MyError["params"])

    at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:63)

Any hints on how to solve this issue? Am I wrong somewhere?

Thank you in advance for suggestions.

did u try with implement setter method?

Golam Mazid Sajib
– Golam Mazid Sajib

2018-07-23 09:38:23 +00:00
Commented Jul 23, 2018 at 9:38 — Golam Mazid Sajib
– Golam Mazid Sajib, Commented Jul 23, 2018 at 9:38
Yep, implemented. Nothing changed.

Gilberto T.
– Gilberto T.

2018-07-23 09:53:46 +00:00
Commented Jul 23, 2018 at 9:53 — Gilberto T.
– Gilberto T., Commented Jul 23, 2018 at 9:53

Halko Karr-Sajtarevic · Accepted Answer · 2018-07-23 10:07:05Z

I tried it using ACCEPT_SINGLE_VALUE_AS_ARRAY and it works as expected.

ObjectMapper om = new ObjectMapper();
om.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);

MyJson asString = om.readValue("{\n"
            + "  \"code\" : \"REQ500\",\n"
            + "  \"description\" : \"Problem with Service\",\n"
            + "  \"params\" : \"\"\n"
            + "}", MyError.class);

MyJson asArray = om.readValue("{\n"
            + "  \"code\" : \"REQ500\",\n"
            + "  \"description\" : \"Problem with Service\",\n"
            + "  \"params\" : [\"\"]\n"
            + "}", MyError.class);

The only thing you have to handle is the response containing just a single element in params which is empty.

Another way could be this definition of MyError:

public class MyError {

    @JsonProperty("code")
    private String code;

    @JsonProperty("description")
    private String description;

    private List<String> params;

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public List<String> getParams() {
        return params;
    }

    @JsonProperty("params")
    private void setParams(JsonNode params) {
        if (params.isArray()) {
            this.params = new ArrayList<>();
            for(JsonNode child : params) {
                this.params.add(child.asText());
            }
        }
    }
}

Worthless · Accepted Answer · 2018-07-23 09:39:38Z

0

I'd try using

OBJECT_MAPPER.enable(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY);

As shown in "Cannot deserialize instance of java.util.ArrayList"

answered Jul 23, 2018 at 9:39

Worthless

5213 silver badges7 bronze badges

2 Comments

Elletlar Over a year ago

Thanks for your answer. Can you please explain how this API solves the problem.

Gilberto T. Over a year ago

Already tried, it doesn't solve my issue given that, unfortunately, ObjectMapper::enable has the same behaviour of configuring ACCEPT_SINGLE_VALUE_AS_ARRAY equal to true.

Golam Mazid Sajib · Accepted Answer · 2018-07-23 10:15:56Z

0

Just implement a setter method which accept string:

public void setParams(String params) {
    this.params = null;
}

if want to accept array:

public void setParams(String[] params) {
    this.params = Arrays.asList(params);
}

edited Jul 23, 2018 at 10:15

answered Jul 23, 2018 at 9:32

Golam Mazid Sajib

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5 Comments

Golam Mazid Sajib Over a year ago

when jackson deserialize it call no argument construct if there is no jsoncreator constructor. then call setter method.

Golam Mazid Sajib Over a year ago

u need to implement another method which accept array

Gilberto T. Over a year ago

Herein the error: line: 4, column: 13] (through reference chain: solutions.infinitec.fabrick.models.common.MyError["params"])

Gilberto T. Over a year ago

Doesn't work. I've got the following error: Cannot deserialize instance of 'java.lang.String' out of START_ARRAY token.

Gilberto T. Over a year ago

Interesting solution proposed by Halko Karr-Sajtarevic solves my issue.

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