2.12.x regression: no default no-arguments constructor found

[henrik242]

I have this Kotlin object which parses an XML into a data class:

object XmlTool {

    @JvmStatic
    fun parseXml(xml: String?): Product {
        val xmlIn = XMLInputFactory.newInstance()
        val factory = XmlFactory(xmlIn)
        val xmlModule = JacksonXmlModule()

        val mapper = XmlMapper(factory, xmlModule).registerKotlinModule()

        return mapper.readValue(xml, Product::class.java)
    }

    data class Stuff(val str: String?)
    data class Product(val stuff: Stuff?)
}

And this Java test:

class Jackson212MissingConstructorTest {

    @Test
    void fails_with_jackson_2_12() throws Exception {
        String xml = "<product><stuff></stuff></product>";

        Product product = XmlTool.parseXml(xml);

        assertEquals(new Product(null), product);
    }
}

Parsing this in Jackson 2.12.0 fails with com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of jackson.xml.XmlTool$Stuff (although at least one Creator exists): no default no-arguments constructor found.

Jackson 2.11.3 works just fine.

The full exception is:

jackson.xml.Jackson212MissingConstructorTest > fails_with_jackson_2_12() 
    com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `jackson.xml.XmlTool$Stuff` (although at least one Creator exists): no default no-arguments constructor found
     at [Source: (StringReader); line: 1, column: 17] (through reference chain: jackson.xml.XmlTool$Product["stuff"])
        at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:63)
        at com.fasterxml.jackson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1590)
        at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1215)
        at com.fasterxml.jackson.databind.deser.ValueInstantiator.createUsingDefault(ValueInstantiator.java:248)
        at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createUsingDefault(StdValueInstantiator.java:275)
        at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.getEmptyValue(BeanDeserializerBase.java:1027)
        at com.fasterxml.jackson.databind.deser.std.StdDeserializer._deserializeFromEmptyString(StdDeserializer.java:322)
        at com.fasterxml.jackson.databind.deser.std.StdDeserializer._deserializeFromString(StdDeserializer.java:271)
        at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromString(BeanDeserializerBase.java:1480)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:207)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:197)
        at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:542)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeWithErrorWrapping(BeanDeserializer.java:565)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeUsingPropertyBased(BeanDeserializer.java:449)
        at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1390)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:362)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:195)
        at com.fasterxml.jackson.dataformat.xml.deser.XmlDeserializationContext.readRootValue(XmlDeserializationContext.java:91)
        at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4568)
        at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3523)
        at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3491)
        at jackson.xml.XmlTool.parseXml(XmlTool.kt:19)
        at jackson.xml.Jackson212MissingConstructorTest.fails_with_jackson_2_12(Jackson212MissingConstructorTest.java:14)

Here's a test project: https://github.com/henrik242/jackson-xml-problem/tree/2-12-empty-constructor

[henrik242]

@cowtowncoder Have you seen this? Looking forward to rc2 😄

[kupci]

@henrik242 To make sure this is categorized correctly, are you sure this should be here in jackson-dataformat-xml? Or should it go under jackson-module-kotlin?

dependencies {
    implementation("com.fasterxml.jackson.dataformat:jackson-dataformat-xml:$jacksonVersion")
    implementation**("com.fasterxml.jackson.module:jackson-module-kotlin:$jacksonVersion")**

    testImplementation("org.junit.jupiter:junit-jupiter-api:$junitVersion")
    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:$junitVersion")
}

[cowtowncoder]

@henrik242 Had not noticed it. As per @kupci's comment I suspect this might not Kotlin-specific, so I'll try to see if I can reproduce with XML and Java.

I would expect test to probably fail for different reason: instead of null, should give empty String to constructor. But we'll see.

[cowtowncoder]

Actually, no, I would need a plain Java reproduction -- I am guessing this may well be due to problem with @JsonCreator handling (properties vs delegating), and/or not using @JacksonXmlText. Alternative would be to try to reproduce this with json and move to Kotlin but that I don't think would work well.

Test itself could be added under jackson-integration-tests which can combine Kotlin and XML modules (neither of which is allowed to depend on each other, even for tests, since doing so would lead to cyclic dependency that's gnarly for builds).

So, the issue very likely has to do with the way Kotlin module's mapping of data classes to creators; in this case creator would have to be "delegating", not properties-based, looking at structure. I don't know how it might have worked before but I do not think there is a way to make that structure map as expected with properties-style constructors.

[cowtowncoder]

Example works with Java definitions like:

    static class Stuff427 {
        String str;

        @JsonCreator(mode = JsonCreator.Mode.DELEGATING)
        public Stuff427(String s) { str = s; }
    }

    static class Product427 {
        Stuff427 stuff;

        public Product427(@JsonProperty("stuff") Stuff427 s) { stuff = s; }
    }

    public void testEmptyIssue427() throws Exception
    {
        String xml = "<product><stuff></stuff></product>";
        Product427 product = MAPPER.readValue(xml, Product427.class);
        assertNotNull(product);
        assertNotNull(product.stuff);
        assertEquals("", product.stuff.str);
    }

and the distinction is that the outer POJO requires properties-based creator (since there is propert "stuff"), whereas inner POJO requires delegate-based as it must map straight from String value.

So I don't see a bug in XML format module, and suspect that challenge is that of annotating Stuff to delegate String value.

[henrik242]

@cowtowncoder Should I re-post this issue in the Kotlin module? Or add a PR to https://github.com/FasterXML/jackson-integration-tests ? Or maybe both?

[cowtowncoder]

@henrik242 I think I'll first transfer this to Kotlin module, for maintainers to see.

[henrik242]

@cowtowncoder @dinomite The 2.12 release fails with this issue now.

[michaelbrewer]

What is the timeline for 2.12.1 release and can we add this to the test coverage to prevent regression