Question

I have to migrate the following code from Jackson 1.9 to 2.0

public class ObjectIdDeserializer extends JsonDeserializer<ObjectId> {
    @Override
    public ObjectId deserialize(JsonParser jp, DeserializationContext context) {
        JsonNode oid = jp.readValueAsTree().get("$oid");
        return new ObjectId(oid.getTextValue());
    }
}

Because the return type of readValueAsTree() has change from JsonNode to TreeNode I’m not able anymore to access to its value. I’ve tried hasCurrentToken(), nextToken() and others strange methods like those without finding a way to access gracefully to the tree nodes. The get method that I was using rely on a map, so it does not need any iteration.

Answer 1

According to ObjectMapper class from Jackson :

public <T extends TreeNode> T readTree(JsonParser jp) throws IOException, JsonProcessingException
{
    /* ... */
    JsonNode n = (JsonNode) _readValue(cfg, jp, JSON_NODE_TYPE);
    if (n == null) {
        n = getNodeFactory().nullNode();
    }
    @SuppressWarnings("unchecked")
    T result = (T) n;
    return result;
}

readTree method is called by readValueAsTree method, and as JsonNode implements TreeNode, just cast the TreeNode object returned to an JsonNode object and you’ll get the result that you expect !

@Override
public ObjectId deserialize(JsonParser jp, DeserializationContext context) {
    JsonNode oid = ((JsonNode)jp.readValueAsTree()).get("$oid");
    return new ObjectId(oid.asText());
}