Jackson Deserializer based on several StackOverflow posts.

ArrayOrObject.java

import java.util.List;

@Data
public class ArrayOrObject<T> {
    private List<T> data;

    private Boolean isObject;
}

ArrayOrObjectDeserializer.java

/*
 * http://stackoverflow.com/questions/20230114/jersey-jackson-and-jax-rs-post-multiple-json-formats
 * http://stackoverflow.com/questions/36159677/how-to-create-a-custom-deserializer-in-jackson-for-a-generic-type
 * http://stackoverflow.com/questions/31300046/how-to-use-jacksons-contextualdeserializer-for-root-values
 */
public static class ArrayOrObjectDeserializer
    extends JsonDeserializer<ArrayOrObject>
    implements ContextualDeserializer {

    private Class<?> contentType;

    @Override
    public JsonDeserializer<?> createContextual(
        DeserializationContext ctxt,
        BeanProperty property
    ) throws JsonMappingException {
        final JavaType wrapperType;

        if (property == null) {
            wrapperType = ctxt.getContextualType();
        } else {
            wrapperType = property.getType();
        }

        final JavaType contentType = wrapperType.containedType(0);
        final ArrayOrObjectDeserializer deserializer = new ArrayOrObjectDeserializer();
        deserializer.contentType = contentType.getRawClass();
        return deserializer;
    }

    @Override
    public ArrayOrObject deserialize(
        final JsonParser jp,
        final DeserializationContext ctxt
    ) throws IOException, JsonProcessingException {
        final ArrayOrObject wrapper = new ArrayOrObject();

        // Retrieve the object mapper and read the tree.
        ObjectMapper mapper = (ObjectMapper) jp.getCodec();
        JsonNode root = mapper.readTree(jp);

        if (root.isArray()) {
            final List list = new LinkedList();

            // Deserialize each node of the array using the type expected.
            final Iterator<JsonNode> rootIterator = root.iterator();
            while (rootIterator.hasNext()) {
                list.add(mapper.treeToValue(rootIterator.next(), this.contentType));
            }

            wrapper.setData(list);
            wrapper.setIsObject(false);
        } else {
            wrapper.setData(Arrays.asList(mapper.treeToValue(root, this.contentType)));
            wrapper.setIsObject(true);
        }

        return wrapper;
    }
}

This will allow you to accept POST bodies that are either Arrays or single Objects. The isObject flag is there to determine what kind of response you wish to return if necessary.

Good job man!

Thanks for being so helpful!

고마워요