`ObjectMapper`'s `.valueToTree()` wraps `JsonNode` objects into a POJONode

[fge]

Affected versions: 2.2.3, 2.3.2.

Let us take these two sample classes:

public final class BasicBean
{
    private String foo;

    public void setFoo(final String foo)
    {
        this.foo = foo;
    }

    public String getFoo()
    {
        return foo;
    }

    public static void main(final String... args)
    {
        final BasicBean foo = new BasicBean();
        foo.setFoo("bar");
        final ObjectMapper mapper = new ObjectMapper();
        final JsonNode node = mapper.valueToTree(foo);
        System.out.println(node.getNodeType());
        System.out.println(node);
    }
}

and this one:

public final class CustomSerializedPojo
    implements JsonSerializable
{
    private final ObjectNode node = JsonNodeFactory.instance.objectNode();

    public void setFoo(final String foo)
    {
        node.put("foo", foo);
    }

    @Override
    public void serialize(final JsonGenerator jgen,
        final SerializerProvider provider)
        throws IOException, JsonProcessingException
    {
        jgen.writeTree(node);
    }

    @Override
    public void serializeWithType(final JsonGenerator jgen,
        final SerializerProvider provider, final TypeSerializer typeSer)
        throws IOException, JsonProcessingException
    {
        typeSer.writeTypePrefixForObject(this, jgen);
        serialize(jgen, provider);
        typeSer.writeTypeSuffixForObject(this, jgen);
    }

    public static void main(final String... args)
    {
        final CustomSerializedPojo pojo = new CustomSerializedPojo();
        pojo.setFoo("bar");
        final ObjectMapper mapper = new ObjectMapper();
        final JsonNode node = mapper.valueToTree(pojo);
        System.out.println(node.getNodeType());
        if (node.getNodeType() == JsonNodeType.POJO) {
            final Object embedded = ((POJONode) node).getPojo();
            System.out.println(embedded.getClass());
            System.out.println(embedded);
        }
    }
}

The execution of the first main gives:

OBJECT
{"foo":"bar"}

However, the execution of the second one gives:

POJO
class com.fasterxml.jackson.databind.node.ObjectNode
{"foo":"bar"}

Therefore, if .valueToTree() is called on a class implementing JsonSerializable, it embeds the result of the serialization into a POJONode!

NOTE: I did check that it was the .serialize() method which was called and not .serializeWithType().

[fge]

Uh, wait, actually it doesn't do this for all JsonSerializable classes; JsonNode and derivates are not affected, for instance...

[cowtowncoder]

Fixed: the problem was due to value conversion writing to TokenBuffer (which is ok so far) and JsonNodeDeserializer only seeing "some POJO": instead, needs special handling. Fixed for 2.3.3 and 2.4.0.

[cowtowncoder]

Hmmh. Come to think of it now, this will only solve the case of JsonNode, but will still have problems with other JsonSerializable cases. Will create a separate issue for solving more general issue.

[cowtowncoder]

Never mind. Was too fast with commentary. It really depends on exactly how serialize() (and/or serializeWithType()) is implemented: specific issue here was that writeTree() implementation of TokenBuffer just embeds node; but then JsonNodeDeserializer not realizing it should fetch "hidden" node. So there is no generic problem, nor solution.

[fge]

Uhm, how do I understand your last statement then?

I'd love to use that method; and I know I want JsonNodes out of it. Should I then inspect it if it is a POJONode as a workaround?

[cowtowncoder]

Comment was on previous comment; but the short answer is that as far as I know, use of generator.writeTree() should now work as expected, even when using value conversion methods.

So you should not have to inspect anything: JsonNodeDeserializer should be able to figure things out.