jackson-deserialization

How to deserialize json to Java8 dateTimes

Java 8 DateTime can be deserialized to POJO directly when having the JSR310 dependency, and must register it within the ObjectMapper before using the mapper.

Jackson Dependency

<dependency>
    <groupId>com.fasterxml.jackson.datatype</groupId>
    <artifactId>jackson-datatype-jsr310</artifactId>
    <version>2.11.0</version>
</dependency>

Actually it inlcudes all required jackson dependencies, as shown in the following screen dump

And ObjectMapper must register javaTimeModule

objectMapper.registerModule(new JavaTimeModule());

It shows that the zonedDateTime having been projected to UTC by default. So maybe the best is to write a custom DateTime deserializer.

JSR310

Datatype module to make Jackson recognize Java 8 Date & Time API data types (JSR-310).

This module adds support for quite a few classes:

• Duration
• Instant
• LocalDateTime
• LocalDate
• LocalTime
• MonthDay
• OffsetDateTime
• OffsetTime
• Period
• Year
• YearMonth
• ZonedDateTime
• ZoneId
• ZoneOffset

Custom Deserializer

Instead of using JSR-310 to deserialize ZonedDateTime, it may be a good practice to create a custom deserializer and applying it directly on the data model attribute without registering a JSR-310 JavaDateTimeModule within ObjectMapper. By this way, Jackson can directly deserialize json string to ZonedDateTime instance.

    @JsonDeserialize(using = ZonedDateTimeDeserializer.class)
    private ZonedDateTime startTime;

Jackson leaves client an interface to carry out a custom deserializer.

public class ZonedDateTimeDeserializer extends JsonDeserializer<ZonedDateTime> {
    @Override
    public ZonedDateTime deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException, JacksonException {
        return ZonedDateTime.parse(jsonParser.getText(), DateTimeFormatter.ISO_OFFSET_DATE_TIME);
    }
}

References

https://www.baeldung.com/jackson-serialize-dates

https://www.baeldung.com/jackson-deserialization