Ignoring null fields when deserializing with Jackson

Question

I have the following Kotlin data class:

data class TestObject(
        val boolField: Boolean,
        val stringField: String,
        val nullBoolField: Boolean = true,
        val nullStringField: String = "default",
        val notThereBoolField: Boolean = true,
        val notThereStringField: String = "not there"
)

I am then attempting to deserialize some JSON into this class using Jackson v2.9.4 with the Jackson Kotlin plugin v2.9.4.1. The test JSON is as follows:

{
    "boolField": true,
    "stringField": "string",
    "nullBoolField": null,
    "nullStringField": null
}

The first two and the last two fields deserialize successfully - with the values from the JSON and the default values from the Kotlin data class, as appropriate. However, when the middle pair of fields are present, the deserialization fails with:

Instantiation of [simple type, class com.example.TestObject] value failed for JSON property nullStringField due to missing (therefore NULL) value for creator parameter nullStringField which is a non-nullable type

I know I could solve the problem by changing the types of nullBoolField and nullStringField to Boolean? and String? respectively, but since default values are known I would rather not have to push the handling of null further down into the code by doing that.

The question is: is there any way of configuring Jackson to use the Kotlin data class default values for non-nullable properties when the property is present in the JSON but set to null?

Did you find any answer on it, I still have the same issue, and i can't resolve it at the moment...? — Rémi P, Mar 07 '18 at 14:24

kurt · Answer 1 · 2018-02-12T08:54:37.890

1

You could try first to filter null values from json and after to deserialize it to Kotlin object.

Or you may to try add feature to kotlin-jackson module, with adding a new feature parameter, which will enable a null ignoring from json parameters and use default values. You may do this by modify this line (if I'm not mistaken)

edited Feb 12 '18 at 08:54

answered Feb 11 '18 at 20:17

kurt

1,510
2
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23

`you may to try add feature to kotlin-jackson module, with adding a new feature parameter, which will enable a null ignoring from json parameters and use default values`. How would that work? Any examples? – denvercoder9 Aug 18 '19 at 06:40

score 0 · Answer 2 · answered Feb 11 '18 at 21:16

0

If you don't have any value and field is non-nullable then you should not pass it in request body:

{
    "boolField": true,
    "stringField": "string"
}

This results in following object, as expected:

{
    "boolField": true,
    "stringField": "string",
    "nullBoolField": true,
    "nullStringField": "default",
    "notThereBoolField": true,
    "notThereStringField": "not there"
}

answered Feb 11 '18 at 21:16

pwolaq

6,343
19
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That would be the easy way out I agree. However, in this case, I don't control the source JSON so am trying to find a way to get the intended result when deserializing. – George Feb 12 '18 at 20:21
@George in such situation you could use a DTO and then create TestObject based on its properties – pwolaq Feb 12 '18 at 20:42

score 0 · Answer 3 · answered Jul 24 '23 at 18:26

If you're mapping to Java 8, you can use:

    val kotlinModule = KotlinModule.Builder()
        .disable(KotlinFeature.StrictNullChecks)
        .build()
    val objectMapper = ObjectMapper()
    objectMapper.registerModules(
        Jdk8Module(),
        kotlinModule
    )

Ignoring null fields when deserializing with Jackson

3 Answers3