Hesson Deserialization with Kotlin, initializer block not called

Question

My initialization block works fine when I create my object

class ObjectToDeserialize(var someString: String = "") : Serializable {
    init{
        someString += " initialized"
    }
}

in the following way:

@Test
fun createObject_checkIfInitialized() {
      assertEquals("someString initialized",ObjectToDeserialize("someString").someString)
}

But when I deserialize the object using Gson, the initializer block does not start:

@Test
fun deserializeObject_checkIfInitialized(){
    val someJson: String = "{\"someString\":\"someString\" }"
    val jsonObject = Gson().fromJson(someJson, ObjectToDeserialize::class.java)

    assertEquals("someString initialized",jsonObject.someString)

    // Expected :someString initialized
    // Actual   :someString
}

I think gson creates an object in a different way than when executing the main constructor. Is it possible to have something similar to initializer blocks?

---

Answer 1

Gson is designed to be used with pure Java and does not interpret the basic Kotlin constructors properly.

, ( : "" someString), Gson .

Gson ( Kotlin , ).

---

jackson-module-kotlin, ( Kotlin, Kotlin , 2.8.x).

jackson-module-kotlin Kotson:

class SomeClass(val id: Int = -1) {
    init { println("init $id") }
}

class SomeClassNoDefault(val id: Int) {
    init { println("init $id") }
}

fun main(args: Array<String>) {
    val mapper = jacksonObjectMapper()
    val gson = Gson()

    val idDefault = "{}"
    val id123 = "{\"id\": 123 }"

    println("jackson-module-kotlin, { }:")
    val o1 = mapper.readValue<SomeClass>(idDefault)
    println("after construction: ${o1.id}\n")

    println("jackson-module-kotlin, { \"id\" = 123 }:")
    val o2 = mapper.readValue<SomeClass>(id123)
    println("after construction: ${o2.id}\n")

    println("kotson, { }:")
    val o3 = gson.fromJson<SomeClass>(idDefault)
    println("after construction: ${o3.id}\n")

    println("kotson, { \"id\" = 123 }:")
    val o4 = gson.fromJson<SomeClass>(id123)
    println("after construction: ${o4.id}\n")

    println("---\n")

    println("jackson-module-kotlin, no default value, { \"id\" = 123 }:")
    val o5 = mapper.readValue<SomeClassNoDefault>(id123)
    println("after construction: ${o5.id}\n")

    println("kotson, no default value, { \"id\" = 123 }:")
    val o6 = gson.fromJson<SomeClassNoDefault>(id123)
    println("after construction: ${o6.id}\n")
}

jackson-module-kotlin, { }:
init -1
after construction: -1

jackson-module-kotlin, { "id" = 123 }:
init 123
after construction: 123

kotson, { }:
init -1
after construction: -1

kotson, { "id" = 123 }:
init -1
after construction: 123

---

jackson-module-kotlin, no default value, { "id" = 123 }:
init 123
after construction: 123

kotson, no default value, { "id" = 123 }:
after construction: 123