Question

I am serializing and deserializing following domain object to JSON using Jackson 1.8.3

public class Node {
    private String key;
    private Object value;
    private List<Node> children = new ArrayList<Node>();
    /* getters and setters omitted for brevity */
}

Object is then serialized and deserialized using following code

ObjectMapper mapper = new ObjectMapper();
mapper.writeValue(destination, rootNode);

And then later deserialized with

mapper.readValue(destination, Node.class);

The original values of the object are either Strings, Doubles, Longs or Booleans. However, during serialization and deserialization Jackson transforms Long values (such as 4) to Integers.

How can I “force” Jackson to deserialize numeric non-decimal values to Long instead of Integer?

Answer 1

If type is declared as java.lang.Object, Jackson uses ‘natural’ mapping which uses Integer if value fits in 32 bits. Aside from custom handlers you would have to force inclusion of type information (either by adding @JsonTypeInfo next to field / getter; or by enabling so-called “default typing”).