Problem deserializing polymorphic types with @JsonCreator

[ihr]

I get a NPE when trying to de-serialize a hierarchy of objects. Here is the stack trace:

java.lang.NullPointerException
    at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.addBeanProps(BeanDeserializerFactory.java:542)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.buildBeanDeserializer(BeanDeserializerFactory.java:267)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.createBeanDeserializer(BeanDeserializerFactory.java:171)
    at com.fasterxml.jackson.databind.deser.DeserializerCache._createDeserializer(DeserializerCache.java:388)
    at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:264)
    at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCacheValueDeserializer(DeserializerCache.java:244)
    at com.fasterxml.jackson.databind.deser.DeserializerCache.findValueDeserializer(DeserializerCache.java:143)
    at com.fasterxml.jackson.databind.DeserializationContext.findContextualValueDeserializer(DeserializationContext.java:325)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:147)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:23)
    at com.fasterxml.jackson.databind.DeserializationContext.findContextualValueDeserializer(DeserializationContext.java:329)
    at com.fasterxml.jackson.databind.deser.impl.PropertyBasedCreator.construct(PropertyBasedCreator.java:96)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.resolve(BeanDeserializerBase.java:406)
    at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:295)
    at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCacheValueDeserializer(DeserializerCache.java:244)
    at com.fasterxml.jackson.databind.deser.DeserializerCache.findValueDeserializer(DeserializerCache.java:143)
    at com.fasterxml.jackson.databind.DeserializationContext.findContextualValueDeserializer(DeserializationContext.java:325)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:147)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:23)
    at com.fasterxml.jackson.databind.DeserializationContext.findContextualValueDeserializer(DeserializationContext.java:329)
    at com.fasterxml.jackson.databind.deser.impl.PropertyBasedCreator.construct(PropertyBasedCreator.java:96)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.resolve(BeanDeserializerBase.java:406)
    at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:295)
    at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCacheValueDeserializer(DeserializerCache.java:244)
    at com.fasterxml.jackson.databind.deser.DeserializerCache.findValueDeserializer(DeserializerCache.java:143)
    at com.fasterxml.jackson.databind.DeserializationContext.findRootValueDeserializer(DeserializationContext.java:342)
    at com.fasterxml.jackson.databind.ObjectMapper._findRootDeserializer(ObjectMapper.java:2898)
    at com.fasterxml.jackson.databind.ObjectMapper._readValue(ObjectMapper.java:2763)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:1477)
    at com.fasterxml.jackson.core.JsonParser.readValueAs(JsonParser.java:1285)

This exception does not happen with versions of jackson-databind prior to 2.1.0. I've tested with versions: 2.0.2, 2.0.4, 2.0.5, 2.0.6.

Let me know if you need more information.

[cowtowncoder]

This is not much information to go about. Do you have actual exception message, indicating which Java type triggers this? Presumably it is a class that uses @JsonCreator (due to line number).

[ihr]

I don't have actual exception message. But from debugging I gather it's the root class of my hierarchy which is abstract. Let me know if there is something else you would like to know.

[cowtowncoder]

Could you share the root object? To fix this, I will need to be able to reproduce it, and at this point I can't.
Unit test would be ideal; there is something special about either your configuration, or class definitions, that causes this.

[ihr]

Here you go: https://gist.github.com/4113543

[cowtowncoder]

Thanks!

[cowtowncoder]

Ok. Use of creator methods may be problematic with polymorphic types, so although this should work, a temporary work-around would be to change 'id' to be passed via field or (private) setter.

[cowtowncoder]

I added a check to at least indicate the root cause ("could not find creator property with name 'id'") here, as the first step.

[ihr]

Great. Do you plan to correct this problem for the next release?

[cowtowncoder]

If possible yes, i.e. my best intention is to do that. But it all depends on what exactly is going on.

I would recommend however to work around the issue in the meantime by moving id not to be passed via creator. I suspect that combination (abstract types, creator methods) is triggering the issue.

[jacques-n]

Another workaround for this issue is to ensure that you use an interface as the base rather than an abstract class. Then decorate the interface with @JsonTypeInfo.

[chids]

I bumped in to this when playing around with code along the lines of:

public class DummyTest {
    @Test
    public void test() throws JsonParseException, JsonMappingException, IOException {
        new ObjectMapper()
                .setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.NONE)
                .readValue("{\"foo\":\"blah\",\"bar\":\"bleh\"}", Sample.class);
    }

    public static class Sample {
        @JsonProperty
        private String foo;

        @JsonProperty
        private String bar;

        public Sample(@JsonProperty("foo") String foo, @JsonProperty("bar") String bar) {
            this.bar = bar;
            this.foo = foo;
        }
    }
}

[cowtowncoder]

@chids What problem are you seeing here? This should just work fine, as there is no polymorphic type to consider?

[chids]

@cowtowncoder I stumbled on a NPE in BeanDeserializerFactory (matching the one originally reported in this issue) while "tweaking" the ObjectMapper-configuration in a Dropwizard service. I tried to reproduce it by cloning jackson-databind and putting in the test case above just to see whether it'd been fixed in master. Instead of NPE I get could not find creator property with name 'id' and tracked that to your comment above.

From my, somewhat narrow, point of view the culprit seems to be:
setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.NONE)

But I also noticed that the error went away if I removed any one of the constructor arguments in the code above (thus leaving the constructor with only one argument).

[cowtowncoder]

@chids: handling of a single-non-annotated-ctor-argument is different: this will be considered so-called "delegating" creator, meaning that Jackson will actually bind full matching value and pass that; whereas with named parameters, JSON content must be a JSON Object, and properties are extracted from that. So your work-around does change semantics of handling.

You are right in that if auto-discovery is disabled, it has effect on handling of constructors that could otherwise be located as per rules (single-String, single-int/long/Integer/Long constructors).

So: to fix your example, you must add @JsonCreator next to constructor, since otherwise it will be ignored due to disabling of creator auto-detection. No attempt is made to try to look into parameter annotations; only explicit annotation on methods/fields/constructors are used.

[cowtowncoder]

Oh. Actually, one more thing: delegating-constructor should also NOT be auto-detected, with your configuration. So there may be a small flaw in there.