Coercion of primitive types during deserialization

[krystofrezac]

Hi everyone,

I've encountered an issue where primitive types are being automatically converted into other primitive types during deserialization. Specifically, I would like to prevent this behavior and enforce that deserialization only succeeds when the input JSON type matches exactly the type declared in my DTO.

Example

Given the following DTO and deserialization code:

@Serdeable
data class MyDto(
    @JsonProperty(required = true)
    val string: String,
    @JsonProperty(required = true)
    val boolean: Boolean,
)

@Context
class A(
    private val objectMapper: ObjectMapper,
) {
    init {
        objectMapper
            .readValue(
                """
                {
                   "string": 123,
                   "boolean": 1
                }
                """,
                MyDto::class.java,
            ).also { println(it) } // prints: MyDto(string=123, boolean=true)
    }
}

Current Behavior:

• The number 123 is deserialized into the string property.
• The number 1 is deserialized into the boolean property as true.

Configuration

I have the following settings in application.properties:

micronaut.serde.deserialization.strict-nullable=true
micronaut.serde.deserialization.fail-on-null-for-primitives=true

Question

Is there a way to disable this automatic primitive type conversion, so that deserialization fails if the JSON value type does not exactly match the DTO property type (e.g., number to string, number to boolean)? Ideally, I want an error to be thrown if the types don't match.

---

Thank you in advance for any guidance or suggestions!