Custom Jackon Serializer / Deserializer With Nullable Fields

JacksonCustomSerializerTest.java

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import org.junit.Test;

import java.io.IOException;
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneOffset;
import java.util.Objects;

import static org.junit.Assert.assertEquals;

public class JacksonCustomSerializerTest {

    @Test
    public void shouldSerializeWithNullFieldValue() throws Throwable {
        assertEquals("{\"creation\":null}", mapper().writeValueAsString(new Person()));
    }

    @Test
    public void shouldSerializeWithNotNullFieldValue() throws Throwable {
        assertEquals(
            "{\"creation\":1483288200000}",
            mapper().writeValueAsString(new Person(LocalDateTime.of(2017, 1,1,16,30)))
        );
    }

    @Test
    public void shouldDserializeWithNullFieldValue() throws Throwable {
        assertEquals(new Person(), mapper().readValue("{\"creation\":null}", Person.class));
    }

    @Test
    public void shouldDeserializeWithNotNullFieldValue() throws Throwable {
        assertEquals(
            new Person(LocalDateTime.of(2017, 1,1,16,30)),
            mapper().readValue("{\"creation\":1483288200000}", Person.class)
        );
    }

    public ObjectMapper mapper() {
        return new ObjectMapper();
    }

    static class Person {

        public Person() {
        }

        public Person(LocalDateTime creation) {
            this.creation = creation;
        }

        @JsonSerialize(using = LocalDateTimeSerializer.class)
        @JsonDeserialize(using = LocalDateTimeDeserializer.class)
        public LocalDateTime creation;

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            Person person = (Person) o;
            return Objects.equals(creation, person.creation);
        }

        @Override
        public int hashCode() {

            return Objects.hash(creation);
        }
    }

    static class LocalDateTimeSerializer extends JsonSerializer<LocalDateTime> {
        @Override
        public void serialize(LocalDateTime value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
            if(value != null){
                gen.writeNumber(value.toInstant(ZoneOffset.UTC).toEpochMilli());
            }
        }
    }

    static class LocalDateTimeDeserializer extends JsonDeserializer<LocalDateTime> {
        @Override
        public LocalDateTime deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
            if(p.currentToken() == JsonToken.VALUE_NULL){
                return null;
            }
            return LocalDateTime.ofInstant(Instant.ofEpochMilli(p.getLongValue()), ZoneOffset.UTC);
        }
    }
}