Why does Jackson's default deserializer set the Zone to UTC rather than Z?

Question

I think I must be misunderstanding how Zones work in java's ZonedDateTime class. When I use Jackson to serialize and then deserialize now(), the deserialized value has getZone() == "UTC" instead of the "Z" in the serialized value. Can anyone explain to me why this is and what I should be doing instead?

The code below prints:

{"t":"2017-11-24T18:00:08.425Z"}
Data [t=2017-11-24T18:00:08.425Z]
Data [t=2017-11-24T18:00:08.425Z[UTC]]
Z
UTC

The java source:

<!-- language: java -->

package model;

import static org.junit.Assert.*;

import java.io.IOException;
import java.time.ZoneOffset;
import java.time.ZonedDateTime;

import org.junit.Test;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

public class ZonedDateTimeSerializationTest {

    static public class Data {
        @Override
        public String toString() {
            return "Data [t=" + t + "]";
        }

        public ZonedDateTime getT() {
            return t;
        }

        public void setT(ZonedDateTime t) {
            this.t = t;
        }

        ZonedDateTime t = ZonedDateTime.now(ZoneOffset.UTC);
    };

    @Test
    public void testDeSer() throws IOException {
        Data d = new Data();
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.findAndRegisterModules();
        String serialized = objectMapper.writer()
                .without(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)
                .writeValueAsString(d);
        System.out.println(serialized);

        Data d2 = objectMapper.readValue(serialized, Data.class);
        System.out.println(d);
        System.out.println(d2);
        System.out.println(d.getT().getZone());
        System.out.println(d2.getT().getZone());

        // this fails
        assertEquals(d, d2);
    }
}

Answer 1

By default, during deserialization of a ZonedDateTime, Jackson will adjust the parsed timezone to the contextually provided one. You can modify this behavior with this setting so that the parsed ZonedDateTime will stay at Z:

objectMapper.disable(DeserializationFeature.ADJUST_DATES_TO_CONTEXT_TIME_ZONE);

More details here

Answer 2

I did this to actually preserve the timezones:

mapper.enable(SerializationFeature.WRITE_DATES_WITH_ZONE_ID)
mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)