public val/var in constructor produces 'No String-argument constructor/factory method to deserialize from String value'

As per https://github.com/FasterXML/jackson-dataformat-xml/issues/254, I have a very similar problem. I’m on 2.9.1. The case is so simple that I’m not sure my usage is correct, but the functioning workaround suggests it’s legitimate.

The following should serve as a self-contained example.

package com.robpridham.jsonexample

import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
import com.fasterxml.jackson.module.kotlin.readValue
import org.junit.Assert.assertEquals
import org.junit.Test

class DataClassTest {

    data class DataClass1(val name: String, val content: DataClass2)

    data class DataClass2(val content: String)

    private val jsonData = """
        {
            "name": "my name",
            "content": "some value"
        }
        """

    @Test
    fun testJsonParsing() {
        val mapper = jacksonObjectMapper()
        val dataClass1 = mapper.readValue<DataClass1>(jsonData)
        assertEquals(DataClass2("some value"), dataClass1.content)
    }
}

This fails with the following:

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `com.robpridham.jsonexample.DataClassTest$DataClass2` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('some value')
 at [Source: (String)"
{
            "name": "my name",
            "content": "some value"
        }
        "; line: 4, column: 24] (through reference chain: com.robpridham.jsonexample.DataClassTest$DataClass1["content"])

	at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:63)
	at com.fasterxml.jackson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1329)
	at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1031)
	at com.fasterxml.jackson.databind.deser.ValueInstantiator._createFromStringFallbacks(ValueInstantiator.java:370)
	at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromString(StdValueInstantiator.java:314)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromString(BeanDeserializerBase.java:1351)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:170)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:161)
	at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:519)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeWithErrorWrapping(BeanDeserializer.java:527)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeUsingPropertyBased(BeanDeserializer.java:416)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1265)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:325)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:159)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4001)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3011)
	at com.robpridham.jsonexample.DataClassTest.testJsonParsing(DataClassTest.kt:28)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:51)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at com.intellij.rt.execution.application.AppMainV2.main(AppMainV2.java:131)

If I rework DataClass2 to have private val in the constructor, or indeed no val keyword in its constructor at all, then this works.

[Fleshgrinder]

Hey @apatrida the former case you described is what I have and I’m running into exactly this issue, minimal example:

import com.fasterxml.jackson.annotation.JsonValue
import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
import com.fasterxml.jackson.module.kotlin.readValue

data class ValueObject(@JsonValue val value: String)

fun main(args: Array<String>) {
    val mapper = jacksonObjectMapper()
    val vo = mapper.readValue<ValueObject>(""""value"""")

    check(vo == ValueObject("value"))
}

Deserialization fails with:

Exception in thread "main" com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `ValueObject` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('value')
 at [Source: (String)""value""; line: 1, column: 1]
	at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:63)
	at com.fasterxml.jackson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1342)
	at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1031)
	at com.fasterxml.jackson.databind.deser.ValueInstantiator._createFromStringFallbacks(ValueInstantiator.java:371)
	at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromString(StdValueInstantiator.java:323)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromString(BeanDeserializerBase.java:1366)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:171)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:161)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4001)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3011)
	at MainKt.main(main.kt:14)

The only workaround I found so far is the following:

import com.fasterxml.jackson.annotation.JsonCreator
import com.fasterxml.jackson.annotation.JsonValue
import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
import com.fasterxml.jackson.module.kotlin.readValue

data class ValueObject(@JsonValue val value: String) {
    private companion object {
        @JsonCreator
        @JvmStatic
        fun valueOf(value: String) = ValueObject(value)
    }
}

fun main(args: Array<String>) {
    val mapper = jacksonObjectMapper()
    val vo = mapper.readValue<ValueObject>(""""value"""")

    check(vo == ValueObject("value"))
}

[apatrida]

I am wondering if what @robpridham-bbc is doing is instead trying to use the ideas of @JsonUnwrapped which won’t currently work since (@cowtowncoder) you get the error:

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot define Creator property “content” as @JsonUnwrapped: combination not yet supported

If that is not the case, maybe is intending to use @JsonValue annotation but that succeeds in @Fleshgrinder 's case but not the case of a nested object.

But really I think he just wants the single string constructor to work as-is, so I think this is the solution here:

class Github91Test {

    data class DataClass1(val name: String, val content: DataClass2)

    data class DataClass2 @JsonCreator(mode = JsonCreator.Mode.DELEGATING) constructor (@JsonValue val content: String)

    private val jsonData = """
        {
            "name": "my name",
            "content": "some value"
        }
        """

    @Test
    fun testJsonParsing() {
        val mapper = jacksonObjectMapper()
        val dataClass1 = mapper.readValue<DataClass1>(jsonData)
        assertEquals(DataClass1("my name", DataClass2("some value")), dataClass1)
        assertEquals("{\"name\":\"my name\",\"content\":\"some value\"}", mapper.writeValueAsString(dataClass1))
    }
}

Closing this issue because nothing reported here is an actual bug.