Weird Exception during read with Type info

[pgelinas]

I've hit a rather nasty problem when deserializing some XML, which seems to be caused by the order the attributes appear on an xml element. For exemple <Foo type=\"bad\" data=\"dummy\"><bar><bar>FOOBAR</bar></bar></Foo> parses fine, but inverting type and data attributes' order result in this weird exception:

com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of START_OBJECT token
 at [Source: java.io.StringReader@42787d6a; line: 1, column: 36] (through reference chain: FooBad["bar"])
    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:164)
    at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:698)
    at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:694)
    at com.fasterxml.jackson.databind.deser.std.StringCollectionDeserializer.handleNonArray(StringCollectionDeserializer.java:210)
    at com.fasterxml.jackson.databind.deser.std.StringCollectionDeserializer.deserialize(StringCollectionDeserializer.java:164)
    at com.fasterxml.jackson.databind.deser.std.StringCollectionDeserializer.deserialize(StringCollectionDeserializer.java:154)
    at com.fasterxml.jackson.databind.deser.std.StringCollectionDeserializer.deserialize(StringCollectionDeserializer.java:1)
    at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:538)
    at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:99)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:242)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:155)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:126)
    at com.fasterxml.jackson.databind.jsontype.impl.AsPropertyTypeDeserializer._deserializeTypedForId(AsPropertyTypeDeserializer.java:110)
    at com.fasterxml.jackson.databind.jsontype.impl.AsPropertyTypeDeserializer.deserializeTypedFromObject(AsPropertyTypeDeserializer.java:81)
    at com.fasterxml.jackson.databind.deser.AbstractDeserializer.deserializeWithType(AbstractDeserializer.java:132)
    at com.fasterxml.jackson.databind.deser.impl.TypeWrappedDeserializer.deserialize(TypeWrappedDeserializer.java:41)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3008)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2113)

I've also noted that this doesn't cause problem when the property is not a List. I'll attach a unit test shortly.

I've debugged a little bit and it seems that because the type property is not the first encountered during parsing there's some buffering (with TokenBuffer) involved, which doesn't seem to play well with the Collection deserializer. This might also be related to the virtual wrapping necessary for collections?

[cowtowncoder]

Interesting... seems odd that ordering of attributes should matter.

[pgelinas]

Ok, I've been able to debug the thing, here's what I found: when deserializing with type, when the type property is not the first found, the AsPropertyTypeDeserializer buffers the token stream until it finds the property. When it finds the type property, it creates a JsonParserSequence from the token buffer and the underlying xml parser, then resumes processing. When trying to deserialize a Collection, the Collection deserializer calls isExpectedStartArrayToken(), which FromXmlParser overrides to transform a START_OBJECT into a START_ARRAY. Unfortunately, both JsonParserSequence and JsonParserDelegate do not override this method to delegate to the underlying parser; fix is simply to add the appropriate override in JsonParserDelegate in jackson-databind.

[cowtowncoder]

Very good detective work...

[cowtowncoder]

Looks like 'bad' test still fails tho?