Unexpected InvalidTypeIdException when parsing XML to POJO containing nested List<> , custom `TypeIdResolver`

XML Parsing fails with the complain that type id is missing, even when it is defined in the input xml

When ‘uid’ attribute is completely removed from the input xml, then the parsing works.

Java Code where problem can be reproduced with jackson-dataformat-xml 2.11.2

package com.temp;

import java.io.IOException;
import java.util.List;

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.databind.DatabindContext;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.annotation.JsonTypeIdResolver;
import com.fasterxml.jackson.databind.jsontype.impl.TypeIdResolverBase;
import com.fasterxml.jackson.dataformat.xml.XmlMapper;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlElementWrapper;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty;

public class AutoParser {
    public static void main(String[] args) throws Exception {

        String xml = "" +
                "<Auto>\n" +
                "    <Object uid=\"1\" type=\"Engine\">\n" +
                "        <Object uid=\"2\" type=\"Chassis\"></Object>\n" +
                "        <Object uid=\"3\" type=\"Motor\"></Object>\n" +
                "    </Object>\n" +
                "    <Object uid=\"4\" type=\"Body\"></Object>\n" +
                "</Auto>";

        XmlMapper xmlMapper = new XmlMapper();
        Auto auto = xmlMapper.readValue(xml, Auto.class);
        xmlMapper.configure(SerializationFeature.INDENT_OUTPUT, true);
        System.out.println(xmlMapper.writeValueAsString(auto));
    }
}

class Auto {

    @JacksonXmlProperty(localName = "Object")
    @JacksonXmlElementWrapper(useWrapping = false)
    @JsonInclude(JsonInclude.Include.NON_EMPTY)
    List<CarParts> carParts;
}

@JsonTypeIdResolver(CarPartsResolver.class)
@JsonTypeInfo(use = JsonTypeInfo.Id.CUSTOM, include = JsonTypeInfo.As.PROPERTY, property = "type")
abstract class CarParts {

    @JacksonXmlProperty(isAttribute = true) // The is triggering the issue.
    String uid;

    @JacksonXmlProperty(localName = "Object")
    @JacksonXmlElementWrapper(useWrapping = false)
    @JsonInclude(JsonInclude.Include.NON_EMPTY)
    List<CarParts> carParts;
}

class Engine extends CarParts{}
class Chassis extends CarParts{}
class Motor extends CarParts{}
class Body extends CarParts{}

class CarPartsResolver extends TypeIdResolverBase {

    private JavaType superType;

    @Override
    public void init(JavaType javaType) {
        this.superType = javaType;
    }

    @Override
    public String idFromValue(Object o) {
        return idFromValueAndType(o, o.getClass());
    }

    @Override
    public String idFromValueAndType(Object o, Class<?> aClass) {
        return aClass.getSimpleName();
    }

    @Override
    public JavaType typeFromId(DatabindContext context, String id) throws IOException {
        Class<?> subType = null;
        switch (id) {
            case "Engine": subType = Engine.class; break;
            case "Chassis": subType = Chassis.class; break;
            case "Motor": subType = Motor.class; break;
            case "Body": subType = Body.class; break;
        }
        return context.constructSpecializedType(superType, subType);
    }

    @Override
    public JsonTypeInfo.Id getMechanism() {
        return JsonTypeInfo.Id.CUSTOM;
    }
}

Stacktrace

Exception in thread "main" com.fasterxml.jackson.databind.exc.InvalidTypeIdException: Missing type id when trying to resolve subtype of [simple type, class com.temp.CarParts]: missing type id property 'type' (for POJO property 'Object')
 at [Source: (StringReader); line: 3, column: 40] (through reference chain: com.temp.Auto["Object"]->java.util.ArrayList[0]->com.temp.Engine["Object"]->java.util.ArrayList[0])
	at com.fasterxml.jackson.databind.exc.InvalidTypeIdException.from(InvalidTypeIdException.java:43)
	at com.fasterxml.jackson.databind.DeserializationContext.missingTypeIdException(DeserializationContext.java:1794)
	at com.fasterxml.jackson.databind.DeserializationContext.handleMissingTypeId(DeserializationContext.java:1323)
	at com.fasterxml.jackson.databind.jsontype.impl.TypeDeserializerBase._handleMissingTypeId(TypeDeserializerBase.java:303)
	at com.fasterxml.jackson.databind.jsontype.impl.AsPropertyTypeDeserializer._deserializeTypedUsingDefaultImpl(AsPropertyTypeDeserializer.java:166)
	at com.fasterxml.jackson.databind.jsontype.impl.AsPropertyTypeDeserializer.deserializeTypedFromObject(AsPropertyTypeDeserializer.java:107)
	at com.fasterxml.jackson.databind.deser.AbstractDeserializer.deserializeWithType(AbstractDeserializer.java:254)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:293)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:250)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:27)
	at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:138)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:293)

PS: Above code is able to parse following XMLs

<Auto>
    <Object type="Engine">
        <Object type="Chassis"></Object>
        <Object type="Motor"></Object>
    </Object>
    <Object type="Body"></Object>
</Auto>

<Auto>
    <Object uid="1" type="Engine"></Object>
    <Object uid="4" type="Body"></Object>
</Auto>

but fails on

<Auto>
    <Object uid="1" type="Engine">
        <Object uid="2" type="Chassis"></Object>
        <Object uid="3" type="Motor"></Object>
    </Object>
    <Object uid="4" type="Body"></Object>
</Auto>

[cowtowncoder]

Thank you for reporting this issue. I hope to look into this in near future.

[cowtowncoder]

Looks like part of this is buffering: switching order of type and uid for first 2 elements actually makes test pass. This is probably since buffering with TokenBuffer will by-pass all XML specific logic of FromXmlParser – a known potential problem, but in this case actual problem it appears.

Will give up for now, hope to address eventually.