How to send a formatted Zoneddatetime in JSON?

Question

I need to send the following:

"tempo": {
    "inicio": "2019-06-24T20:00-03:00[America/Recife]",
    "fim": "2019-06-25T00:00-03:00[America/Recife]"
}

I created the two dates in my pojo:

@Data
@JsonInclude(JsonInclude.Include.NON_NULL)
public class TempoPojo implements Serializable {
    private ZonedDateTime start;
    private ZonedDateTime stop;

}

And I’m setting the dates that way:

Calendar calendar = Calendar.getInstance();

TempoPojo tempoPojo = new TimeSlotPojo();

final ZoneId zoneId = ZoneId.systemDefault();

calendar.setTime(model.getTempo());
calendar.set(Calendar.HOUR, 10);
calendar.set(Calendar.MINUTE, 30);
calendar.set(Calendar.SECOND, 30);
tempoPojo.setStart(ZonedDateTime.ofInstant(calendar.toInstant(), zoneId));

But my JSON is getting like this:

"tempo":{"inicio":{"date_time":{"date":{"year":2019,"month":6,"day":24},"time":{"hour":20,"minute":0,"second":0,"nano":0}},"offset":{"total_seconds":-10800},"zone":{"id":"America/Recife"}},"fim":{"date_time":{"date":{"year":2019,"month":6,"day":25},"time":{"hour":0,"minute":0,"second":0,"nano":0}},"offset":{"total_seconds":-10800},"zone":{"id":"America/Recife"}}}}

There’s a way to turn all that into a date like this: "2019-06-25T00:00-03:00[America/Recife]"?

Answer 1

First, remember to include the JSR-310 module from Jackson, so that he can deal with the classes of java.time.

Then set the following in ObjectMapper:

ObjectMapper om = new ObjectMapper();
// adicionar o módulo java.time
JavaTimeModule module = new JavaTimeModule();
om.registerModule(module);
// não converter o timezone
om.configure(DeserializationFeature.ADJUST_DATES_TO_CONTEXT_TIME_ZONE, false);

The option ADJUST_DATES_TO_CONTEXT_TIME_ZONE should be disabled so that there are no Timezone conversions, and it uses whatever is on ZonedDateTime.

In the case of Spring, you can also do this via application properties.

And now you have 2 options:

---

Option 1, use the Serializer default

Just add these options to ObjectMapper:

om.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
om.configure(SerializationFeature.WRITE_DATES_WITH_ZONE_ID, true);

And put in your fields:

@JsonProperty("inicio")
private ZonedDateTime start;

@JsonProperty("fim")
private ZonedDateTime stop;

With this, JSON will stay like this:

{
  "inicio" : "2019-06-24T20:00:00-03:00[America/Recife]",
  "fim" : "2019-06-25T00:00:00-03:00[America/Recife]"
}

Notice that in the hours also the second are placed. But you only wanted "hours:minutes", without the seconds, so in this case you will have to create a Serializer customized.

---

Option 2, to use Serializer customized

In that case you don’t need to change the options WRITE_DATES_AS_TIMESTAMPS and WRITE_DATES_WITH_ZONE_ID. Just create a Serializer customized:

public class CustomZonedDateTimeSerializer extends JsonSerializer<ZonedDateTime> {
    private static DateTimeFormatter FMT = DateTimeFormatter.ofPattern("uuuu-MM-dd'T'HH:mmXXX'['VV']'");

    @Override
    public void serialize(ZonedDateTime value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
        jgen.writeString(FMT.format(value));
    }
}

And in the fields, configure them to use this class:

@JsonProperty("inicio")
@JsonSerialize(using = CustomZonedDateTimeSerializer.class)
private ZonedDateTime start;

@JsonProperty("fim")
@JsonSerialize(using = CustomZonedDateTimeSerializer.class)
private ZonedDateTime stop;

With this, JSON will show the hours and minutes, but not the seconds:

{
  "inicio" : "2019-06-24T20:00-03:00[America/Recife]",
  "fim" : "2019-06-25T00:00-03:00[America/Recife]"
}

Just check if this is really what you need, because when omitting the seconds, whoever is going to receive this JSON will assume that they are zero (usually the API’s, when seeing that the seconds are not present, set the value to zero - the java.time does that, for example). The same goes for fractions of a second.

---

Taking advantage, you don’t need to create a Calendar and then create the ZonedDateTime.

Like you did calendar.setTime(model.getTempo()), then I understand that model.getTempo() returns a java.util.Date. So just convert it to Instant and then use atZone to set the ZoneId.

Then to change the time, use the method with passing a java.time.LocalTime. One detail is that in your code you change the time, minute and second, but the fractions of a second are kept, so you have to remember to keep them when creating the LocalTime. Would look like this:

ZoneId zoneId = ZoneId.systemDefault();
// converte o Date para ZonedDateTime, usando o ZoneId indicado
ZonedDateTime zdt = model.getTempo().toInstant().atZone(zoneId);
// muda o horário (preservando as frações de segundo)
tempoPojo.setStart(zdt.with(LocalTime.of(10, 30, 30, zdt.getNano())));

// ou, você pode mudar cada campo individualmente
tempoPojo.setStart(zdt.withHour(10).withMinute(30).withSecond(30));

But as said above, if you choose the second option (which does not show the seconds in JSON), then it is useless to set the value of the seconds, because these will be lost when generating JSON (the same goes for the fractions of a second).

Answer 2

I assume you’re using a project with dependencies managed by Maven.

Include dependency Jackson-datatype-jsr310:

  <dependency>
    <groupId>com.fasterxml.jackson.datatype</groupId>
    <artifactId>jackson-datatype-jsr310</artifactId>
    <version>2.9.9</version>
  </dependency>

In the serializable object, include the desired date format:

@Data
@JsonInclude(JsonInclude.Include.NON_NULL)
class TempoPojo implements Serializable {

    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd'T'HH:mmxxx'['VV']'")
    private ZonedDateTime start;
    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd'T'HH:mmxxx'['VV']'")
    private ZonedDateTime stop;

}

Register the Javatimemodule in your Objectmapper:

public class Main {

    public static void main(String[] args) throws IOException {

        TempoPojo tempoPojo = new TempoPojo();
        final ZoneId zoneId = ZoneId.systemDefault();

        Calendar calendar = Calendar.getInstance();
        calendar.setTime(new Date());
        calendar.set(Calendar.HOUR, 10);
        calendar.set(Calendar.MINUTE, 30);
        calendar.set(Calendar.SECOND, 30);
        tempoPojo.setStart(ZonedDateTime.ofInstant(calendar.toInstant(), zoneId));      
        tempoPojo.setStop(ZonedDateTime.ofInstant(calendar.toInstant(), zoneId));       
        
        ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(new JavaTimeModule());
        System.out.println(mapper.writeValueAsString(tempoPojo));
    }
}