Contextual deserializer for generic wrapper type in Jackson

PagedResultDeserializer.java

package com.example;

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.ObjectCodec;
import com.fasterxml.jackson.databind.BeanProperty;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.deser.ContextualDeserializer;
import com.fasterxml.jackson.databind.type.CollectionType;
import com.fasterxml.jackson.databind.type.TypeFactory;

import java.io.IOException;
import java.util.List;
import java.util.Map;

/**
 * Since {@link PagedResult} and friends are created via {@link PagedResultCreator}, and have always had non-default
 * constructors, it is hard to deserialize them within unit tests using Jackson. This deserializer determines requested
 * type (it implements {@link ContextualDeserializer} so that it gets this information from Jackson, based ultimately on
 * whatever we pass into e.g. {@code RestAssured... .andReturn().as(ThisType.class)}. It then creates its own
 * implementation of {@link PagedResult}, i.e. {@link PagedResultImplForTest}.
 */
public class PagedResultDeserializer extends JsonDeserializer<PagedResult<?>>
        implements ContextualDeserializer {
    private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
    private JavaType valueType;

    public PagedResultDeserializer(JavaType valueType) {
        this.valueType = valueType;
    }

    public PagedResultDeserializer() {

    }

    @Override
    public JsonDeserializer<?> createContextual(DeserializationContext ctxt, BeanProperty property)
            throws JsonMappingException {
        JavaType pagedResultType = property.getType();
        JavaType valueType = pagedResultType.containedType(0);
        return new PagedResultDeserializer(valueType);
    }

    @Override
    public PagedResult<?> deserialize(JsonParser jsonParser, DeserializationContext ctxt) throws IOException {
        TypeFactory typeFactory = ctxt.getTypeFactory();
        CollectionType itemsListType = typeFactory.constructCollectionType(List.class, valueType);
        ObjectCodec objectCodec = jsonParser.getCodec();
        Map properties = objectCodec.readValue(jsonParser, Map.class);
        Object items = properties.remove("items");
        List<?> itemsList = OBJECT_MAPPER.convertValue(items, itemsListType);
        return new PagedResultImplForTest<>(properties, itemsList);
    }
}