Force Milliseconds When Serializing Instant to ISO8601 using Jackson

I solve using this aproach:

ObjectMapper objectMapper = new ObjectMapper();
JavaTimeModule module = new JavaTimeModule();
module.addSerializer(Instant.class, new InstantSerializerWithMilliSecondPrecision());
objectMapper.registerModule(module);

And for InstantSerializerWithMilliSecondPrecision i used this:

public class InstantSerializerWithMilliSecondPrecision extends InstantSerializer {

    public InstantSerializerWithMilliSecondPrecision() {
        super(InstantSerializer.INSTANCE, false, new DateTimeFormatterBuilder().appendInstant(3).toFormatter());
    }
}

Now the Instant serialization always includes milliseconds. Example: 2019-09-27T02:59:59.000Z

There appears to be a Jackson issue open for this here*. That link contains two workarounds

Workaround 1

 ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.registerModule(new JavaTimeModule());
    SimpleModule module = new SimpleModule();
    module.addSerializer(ZonedDateTime.class, new JsonSerializer<ZonedDateTime>() {
        @Override
        public void serialize(ZonedDateTime zonedDateTime, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, JsonProcessingException {
            jsonGenerator.writeString(DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSSZZZ").format(zonedDateTime));
        }
    });
    objectMapper.registerModule(module);
    objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
    objectMapper.enable(SerializationFeature.INDENT_OUTPUT);

Workaround 2

JavaTimeModule javaTimeModule = new JavaTimeModule();
javaTimeModule.addSerializer(ZonedDateTime.class,
  new ZonedDateTimeSerializer(DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSSX")));
ObjectMapper mapper = new ObjectMapper().registerModule(javaTimeModule);

^{*Link is dead because they deprecated FasterXML/jackson-datatype-jsr310 and moved it to jackson-modules-java8. See https://github.com/FasterXML/jackson-modules-java8/issues/76}

If you are trying to do this in Spring Boot and want to use @Gustavo's answer.

import com.fasterxml.jackson.databind.Module;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
import org.springframework.context.annotation.Configuration;

@Configuration
public class AppConfig {

    @Bean
    public Module javaTimeModule() {
        JavaTimeModule module = new JavaTimeModule();
        module.addSerializer(new InstantSerializerWithMilliSecondPrecision());
        return module;
    }

}

None of two workarounds mentioned by Sean Carroll works me. I end up with writing my own serializer for Instant.

final ObjectMapper mapper = new ObjectMapper();
final JavaTimeModule javaTimeModule = new JavaTimeModule();
javaTimeModule.addSerializer(Instant.class, new KeepMillisecondInstantSerializer());
mapper.registerModule(javaTimeModule);

public class KeepMillisecondInstantSerializer extends JsonSerializer<Instant> {

    private final DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSSX")
            .withZone(ZoneId.of("UTC"));

    @Override
    public void serialize(final Instant instant, final JsonGenerator jsonGenerator, final SerializerProvider serializerProvider) throws IOException {
        final String serializedInstant = dateTimeFormatter.format(instant);
        jsonGenerator.writeString(serializedInstant);
    }
}

I guess Jackson use Instant.toString() method to serialize Instant objects by default. I also find some discussions about Instant.toString() method on StackOverflow.

Rather than fixing the bug of Jackson library, following could be a quick work around: Create a string variable in the POJO class where you have Timestamp variable:

private Timestamp createTimeStamp;

private String stringCreateTimeStamp;   

capture timestamp value as a string:

listOfPojo.forEach(pojo-> {
            pojo.setStringCreateTimeStamp(request.getcreateTimeStamp().toString());
        });

Refer https://www.baeldung.com/java-string-to-timestamp for conversions

Solve it by using custom serializers for LocalDateTime and ZonedDateTime classes.

My solution works for me because I use only these two classes in API responses to represent date and time! I don't use Instant or Date so pay attention on it.

@Configuration
class JacksonConfig {

@Bean
fun objectMapper(): ObjectMapper {
    val mapper = ObjectMapper()
    val javaTimeModule = JavaTimeModule().apply {
        addSerializer(LocalDateTime::class.java, KeepMillisecondLocalDateTimeSerializer())
        addSerializer(ZonedDateTime::class.java, KeepMillisecondZonedDateTimeSerializer())
    }
    mapper.registerModule(javaTimeModule)
    return mapper
}

class KeepMillisecondZonedDateTimeSerializer : JsonSerializer<ZonedDateTime>() {
    private val formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSSX")

    @Throws(IOException::class)
    override fun serialize(
        value: ZonedDateTime,
        jsonGenerator: JsonGenerator,
        serializerProvider: SerializerProvider?
    ) {
        jsonGenerator.writeString(formatter.format(value))
    }
}

class KeepMillisecondLocalDateTimeSerializer : JsonSerializer<LocalDateTime>() {
    private val formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSS")

    @Throws(IOException::class)
    override fun serialize(
        value: LocalDateTime,
        jsonGenerator: JsonGenerator,
        serializerProvider: SerializerProvider?
    ) {
        jsonGenerator.writeString(formatter.format(value))
    }
}
}