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?

Answer 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)