Jackson mapping Object or list of Object depending on json input

Question

I have this POJO :

public class JsonObj {

    private String id;
    private List location;


    public String getId() {
        return id;         


        

Answer 1

Update: Mher Sarkissian's soulution works fine, it can also be used with annotations as suggested here, like so:.

@JsonFormat(with = JsonFormat.Feature.ACCEPT_SINGLE_VALUE_AS_ARRAY)
private List<Item> item;

---

My deepest sympathies for this most annoying problem, I had just the same problem and found the solution here: https://stackoverflow.com/a/22956168/1020871

With a little modification I come up with this, first the generic class:

public abstract class OptionalArrayDeserializer<T> extends JsonDeserializer<List<T>> {

    private final Class<T> clazz;

    public OptionalArrayDeserializer(Class<T> clazz) {
        this.clazz = clazz;
    }

    @Override
    public List<T> deserialize(JsonParser jp, DeserializationContext ctxt)
            throws IOException {
        ObjectCodec oc = jp.getCodec();
        JsonNode node = oc.readTree(jp);
        ArrayList<T> list = new ArrayList<>();
        if (node.isArray()) {
            for (JsonNode elementNode : node) {
                list.add(oc.treeToValue(elementNode, clazz));
            }
        } else {
            list.add(oc.treeToValue(node, clazz));
        }
        return list;
    }
}

And then the property and the actual deserializer class (Java generics is not always pretty):

@JsonDeserialize(using = ItemListDeserializer.class)
private List<Item> item;

public static class ItemListDeserializer extends OptionalArrayDeserializer<Item> {
    protected ItemListDeserializer() {
        super(Item.class);
    }
}

Answer 2

This is already supported by jackson

objectMapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);