YAML multi-document does not work with readValue

[chrylis]

Over in #66, a working example is posted for using the SnakeYAML engine to deserialize with Jackson. However, while this works to produce a MappingIterator, the general contract for ObjectMapper#readValue is broken:

ObjectMapper mapper = new ObjectMapper(new YAMLFactory()).findAndRegisterModules()
mapper.readValue(EntitySchema.getResourceAsStream('entitySchemas.yml'), new TypeReference<List<EntitySchema>>() {})

This produces an exception:

Caused by: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.util.ArrayList` out of START_OBJECT token
 at [Source: (BufferedInputStream); line: 2, column: 1]
	at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:63)
	at com.fasterxml.jackson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1343)
	at com.fasterxml.jackson.databind.DeserializationContext.handleUnexpectedToken(DeserializationContext.java:1139)
	at com.fasterxml.jackson.databind.DeserializationContext.handleUnexpectedToken(DeserializationContext.java:1093)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.handleNonArray(CollectionDeserializer.java:332)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:265)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:245)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:27)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4013)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3077)
	... 1 more

I'm opening this issue here because it appears to be a case where the ObjectMapper isn't delegating properly when provided with an explicit factory.

[cowtowncoder]

@chrylis No, this seems to work as intended -- readValue() is limited to a single document and is not designed or intended to support binding over multiple documents. It does not do that for json either (where newline-separated content can be viewed as a sequence of documents.

To read content from multiple logical YAML documents, MappingIterator approach (or a sequence of separate readValue() calls) is needed.

[chrylis]

Okay, I think I can see the data model here, and it makes sense, but it wasn't the obvious interpretation to me. Perhaps a mention of the "multiple documents != single document with a list of objects" model in the documentation would be helpful.

[cowtowncoder]

@chrylis Yes I totally agree that distinction is not something that is well surfaced, and should be documented better. I think I'll create a doc issue to try to outline this with YAML.