Serialize and Deserialize PageImpl in Jackson

It’s very common to put paginated query results in Redis via Jackson serialization and deserialization. However, org.springframework.data.domain.PageImpl doesn’t expose a default constructor. Even worse, that applies to org.springframework.data.domain.Sort and org.springframework.data.domain.Sort.Order as well. There are a couple of workarounds. I’d like to introduce a less intrusive approach for your reference.

The idea is to write a Jackson module which injects a custom serializer and deserializer for org.springframework.data.domain.PageImpl. Let’s see how to do that.

1. Define an interface.

public interface IJPADataPage {
    String _CLASS = "@class";
    String CONTENT = "content";
    String DIRECTION = "direction";
    String IGNORE_CASE = "ignoreCase";
    String NULL_HANDLING = "nullHandling";
    String NUMBER = "number";
    String PROPERTY = "property";
    String SIZE = "size";
    String SORT = "sort";
    String TOTAL_ELEMENTS = "totalElements";
}

2. Define a Serializer.

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.jsontype.TypeSerializer;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;
import org.springframework.data.domain.PageImpl;
import org.springframework.data.domain.Sort;

import java.io.IOException;

@SuppressWarnings("unchecked")
public class JPADataPageSerializer
        extends StdSerializer<PageImpl>
        implements IJPADataPage {
    public JPADataPageSerializer(Class<PageImpl> t) {
        super(t);
    }

    public JPADataPageSerializer() {
        this(null);
    }

    @Override
    public void serialize(
            PageImpl value,
            JsonGenerator jsonGenerator,
            SerializerProvider serializerProvider) throws IOException {
        jsonGenerator.writeStartObject();
        jsonGenerator.writeStringField(_CLASS, PageImpl.class.getName());
        jsonGenerator.writePOJOField(CONTENT, value.getContent());
        jsonGenerator.writeNumberField(NUMBER, value.getNumber());
        jsonGenerator.writeNumberField(SIZE, value.getSize());
        jsonGenerator.writeNumberField(TOTAL_ELEMENTS, value.getTotalElements());
        jsonGenerator.writeArrayFieldStart(SORT);
        if (!value.getSort().isEmpty()) {
            for (Sort.Order order : value.getSort()) {
                jsonGenerator.writeStartObject();
                jsonGenerator.writeStringField(PROPERTY, order.getProperty());
                jsonGenerator.writeStringField(DIRECTION, order.getDirection().name());
                jsonGenerator.writeBooleanField(IGNORE_CASE, order.isIgnoreCase());
                jsonGenerator.writeStringField(NULL_HANDLING, order.getNullHandling().name());
                jsonGenerator.writeEndObject();
            }
        }
        jsonGenerator.writeEndArray();
        jsonGenerator.writeEndObject();
    }

    @Override
    public void serializeWithType(
            PageImpl value,
            JsonGenerator jsonGenerator,
            SerializerProvider serializerProvider,
            TypeSerializer typeSer) throws IOException {
        serialize(value, jsonGenerator, serializerProvider);
    }
}

3. Define a Deserializer.

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import com.fasterxml.jackson.databind.jsontype.TypeDeserializer;
import com.fasterxml.jackson.databind.node.ArrayNode;
import org.springframework.data.domain.PageImpl;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Sort;

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

@SuppressWarnings("unchecked")
public class JPADataPageDeserializer
        extends StdDeserializer<PageImpl>
        implements IJPADataPage {
    public JPADataPageDeserializer(Class<?> type) {
        super(type);
    }

    public JPADataPageDeserializer() {
        this(null);
    }

    @Override
    public PageImpl deserialize(
            JsonParser jsonParser,
            DeserializationContext deserializationContext) throws IOException {
        JsonNode jsonNode = jsonParser.getCodec().readTree(jsonParser);
        List<?> content = deserializationContext.readTreeAsValue(jsonNode.get(CONTENT), List.class);
        int number = jsonNode.get(NUMBER).asInt(0);
        int size = jsonNode.get(SIZE).asInt(1);
        int totalElements = jsonNode.get(TOTAL_ELEMENTS).asInt(0);
        List<Sort.Order> orders = new ArrayList<>();
        ArrayNode arrayNode = (ArrayNode) jsonNode.get(SORT);
        if (!arrayNode.isEmpty()) {
            for (JsonNode jsonNodeOrder : arrayNode) {
                String property = jsonNodeOrder.get(PROPERTY).asText();
                Sort.Direction direction = Sort.Direction.valueOf(jsonNodeOrder.get(DIRECTION).asText());
                boolean ignoreCase = jsonNodeOrder.get(IGNORE_CASE).asBoolean();
                Sort.NullHandling nullHandling = Sort.NullHandling.valueOf(jsonNodeOrder.get(NULL_HANDLING).asText());
                Sort.Order order = new Sort.Order(direction, property, nullHandling);
                if (ignoreCase) {
                    order = order.ignoreCase();
                }
                orders.add(order);
            }
        }
        PageRequest pageRequest = PageRequest.of(number, size, Sort.by(orders));
        return new PageImpl(content, pageRequest, totalElements);
    }

    @Override
    public Object deserializeWithType(
            JsonParser jsonParser,
            DeserializationContext deserializationContext,
            TypeDeserializer typeDeserializer) throws IOException {
        return deserialize(jsonParser, deserializationContext);
    }
}

4. Define a module.

import com.fasterxml.jackson.core.Version;
import com.fasterxml.jackson.databind.module.SimpleModule;
import org.springframework.data.domain.PageImpl;

public class JPADataModule extends SimpleModule {
    public static final String NAME = "JPA Data Module";
    public static final Version VERSION = new Version(0, 1, 0, null, null, null);

    public JPADataModule() {
        super(NAME, VERSION);
        addSerializer(PageImpl.class, new JPADataPageSerializer());
        addDeserializer(PageImpl.class, new JPADataPageDeserializer());
    }
}

5. Register the module.

objectMapper.registerModule(new JPADataModule());

Now Jackson is able to handle PageImpl and the Redis cache works.