CODEWITHSUNDEEP
jsonkotlinjson-deserializationdata-classkotlin-null-safety
Gidi Dembovsky
Gidi Dembovsky

Reputation: 1

Handle JSON With null Inside Array With Kotlin

I am trying to handle null or empty JSON value fields value which has received both JSON case:

{
    "field": [
        null
    ]
}

and

{
    "field": []
}

The case when an empty array works fine for me: If I get an object with an array size of 0, it means it is empty. In the second case, when the field's value is [null], I get an array size 1 with all the elements null. That is why I check the null case with the following approach:

val deserializedJson = jacksonObjectMapper().readValue<DataSimpleClass>(theJsonAsText)    
if (deserializedJson.field.size == 1 && deserializedJson.field[0] == null) {
        throw Exception()
    }

Is there any better or more elegant approach to check such a [null] case?

I deserialize the JSON using jacksonObjectMapper() object version 2.9.8. Also, I have created a two-data class that looks like that:

@JsonInclude(JsonInclude.Include.NON_NULL)
data class DataSimpleClass(
    @JsonInclude(JsonInclude.Include.NON_NULL)
    val field: List<SpecificClass>
    )

@JsonInclude(JsonInclude.Include.NON_NULL)
data class SpecificClass(
    @JsonInclude(JsonInclude.Include.NON_NULL)
    @JsonProperty("field1") val field1: String,
    @JsonInclude(JsonInclude.Include.NON_NULL)
    @JsonProperty("field2") val field2: String,
    @JsonProperty("field3") val field3: String? = null,
    val updateTime: Instant = Instant.now(Clock.systemUTC())
)

Also, I don't understand how Kotlin (null-safe language) may let me create a field when all the elements are null. How is it possible that Kotlin doesn't catch null while I send the non-nullable field null value The deserializedJson result, then the JSON key's value is null ?

I was expecting that the null won't be deserialized cause of its null value, as the object DataSimpleClass holds a non-nullable field.

In addition, my IntelliJ shows me that due to the null safe fields, the following condition "is always false" while, in fact, it is actually true during the run.

How is it possible that the value shouldn't be null due to the null safe, but it all gets null during the run time?the IntelliJ warning for wrong condition result

Upvotes: 0

Views: 1198

Answers (1)

TheLibrarian
TheLibrarian

Reputation: 1898

Kotlin is "null-safe" language because it enforces non-null-ability by default. You can still have nulls in Kotlin - e.g. val foo: String? = null

The IDE just says that based on your definition it shouldn't be null and it will not allow you(at compile time) to put null there. Runtime is where don't have control over who/what puts null there.

If there is no guarantee that you will not receive null there you should sanitize it before assuming there are no nulls.

deserializedJson.field..filterNotNull()

If you would rather that it crashed the whole app I think you can set

.addModule(KotlinModule(strictNullChecks = true))

when configuring Jackson.

Upvotes: 1

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