Unable to deserialize collection of concrete subclass when using defaultImpl

[michaelaberman]

This worked in the last 2.7, but is broken in both 2.8.0 and 2.8.5.

I have a field parameterized with a concrete subclass of a base class annotated with @JsonTypeInfo, and I am trying to deserialize a collection that contains only that specific class. In 2.8.x, the readValue method fails with com.fasterxml.jackson.databind.JsonMappingException: Class JacksonSubclassCollectionTest$SomeBaseClass not subtype of [simple type, class JacksonSubclassCollectionTest$SomeSubClass]. This doesn't appear to happen without defaultImpl (but I have legacy data with no type field that I need to be able to keep deserializing in other contexts). Full stack trace follows example.

public class JacksonSubclassCollectionTest {
  public static void main(String[] args) throws Exception {
    ObjectMapper mapper = new ObjectMapper();

    SomeContainer container = mapper.readValue("{\"collection\":[{\"type\":\"SUBCLASS\",\"field\":7}]}", SomeContainer.class);

    System.out.println(container.collection.get(0).field);
  }

  @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type", defaultImpl = SomeBaseClass.class, visible = true)
  @JsonSubTypes({@JsonSubTypes.Type(name = "SUBCLASS", value = SomeSubClass.class)})
  public static class SomeBaseClass {
    @JsonTypeId
    public String type;
  }

  public static class SomeSubClass extends SomeBaseClass {
    public int field;
  }

  public static class SomeContainer {
    public ArrayList<SomeSubClass> collection;
  }
}

Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Class JacksonSubclassCollectionTest$SomeBaseClass not subtype of [simple type, class JacksonSubclassCollectionTest$SomeSubClass]
 at [Source: {"collection":[{"type":"SUBCLASS","field":7}]}; line: 1, column: 1]
	at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:296)
	at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:269)
	at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCacheValueDeserializer(DeserializerCache.java:244)
	at com.fasterxml.jackson.databind.deser.DeserializerCache.findValueDeserializer(DeserializerCache.java:142)
	at com.fasterxml.jackson.databind.DeserializationContext.findRootValueDeserializer(DeserializationContext.java:475)
	at com.fasterxml.jackson.databind.ObjectMapper._findRootDeserializer(ObjectMapper.java:3890)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3785)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2833)
	at JacksonSubclassCollectionTest.main(JacksonSubclassCollectionTest.java:20)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)
Caused by: java.lang.IllegalArgumentException: Class JacksonSubclassCollectionTest$SomeBaseClass not subtype of [simple type, class JacksonSubclassCollectionTest$SomeSubClass]
	at com.fasterxml.jackson.databind.type.TypeFactory.constructSpecializedType(TypeFactory.java:359)
	at com.fasterxml.jackson.databind.jsontype.impl.StdTypeResolverBuilder.buildTypeDeserializer(StdTypeResolverBuilder.java:118)
	at com.fasterxml.jackson.databind.deser.BasicDeserializerFactory.findTypeDeserializer(BasicDeserializerFactory.java:1363)
	at com.fasterxml.jackson.databind.deser.BasicDeserializerFactory.findPropertyContentTypeDeserializer(BasicDeserializerFactory.java:1526)
	at com.fasterxml.jackson.databind.deser.BasicDeserializerFactory.resolveMemberAndTypeAnnotations(BasicDeserializerFactory.java:1841)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.constructSettableProperty(BeanDeserializerFactory.java:735)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.addBeanProps(BeanDeserializerFactory.java:520)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.buildBeanDeserializer(BeanDeserializerFactory.java:226)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.createBeanDeserializer(BeanDeserializerFactory.java:141)
	at com.fasterxml.jackson.databind.deser.DeserializerCache._createDeserializer2(DeserializerCache.java:406)
	at com.fasterxml.jackson.databind.deser.DeserializerCache._createDeserializer(DeserializerCache.java:352)
	at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:264)
	... 12 more

[cowtowncoder]

Unfortunately this is probably same as #1339 and is not as much a bug than eager validation feature.
As per #1339 I hope to (eventually...) improve things so that validation of type compatibility is deferred, but the issue here is that usage is problematic: although you are asking for SomeContainer, base type for polymorphic handling is really SomeBaseClass, and if type is missing, that's what you would get.
Since that would result in a cast exception, code throws an exception.

Earlier versions (2.7 and prior) did not do such validation, which allowed code to work (at least until one entry was missing type).
With 2.8 compatibility check is made, related to other type handling changes (related to type resolution improvements in 2.7). Intent was to more gracefully handle assignment incompatibilities.

On short term I would suggest that you change your code to bind using SomeBaseClass as target class, and just doing explicit cast. It's bit ugly, but will work the same on both 2.7 and 2.8.
Longer term I hope to improve handling here, but that may take time and is not guaranteed to get in 2.8 branch.

Thank you for reporting the problem; I hope my explanation helps.

[dialtahi]

Is still broken in jackson 2.8.10 and 2.9.1

[cowtowncoder]

@dialtahi Of course. If it was fixed there would be update here.

[blop]

Guys, this is a BIG regression for people upgrading from 2.7.

If you have some class with a List<> and another with a Set<>, using a SimpleAbstractTypeResolver that provides the defaultImpl as ArrayList and HashSet, it just does NOT work anymore.

[cowtowncoder]

@blop what you describing sounds different from the original report, so I would suggest filing a separate issue with reproduction. The issue as described here is very unlikely to be addressed until 3.x, but if what you experience is different there might be possibility of a fix.

[KroligG]

Look like this is fixed by #1565. At least updating to 2.9.6 fixed same issue for me.