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Populating custom field through jackson

I have a POJO as below:
#Data
#Builder
#AllArgsConstructor
#NoArgsConstructor
#JsonIgnoreProperties(ignoreUnknown = true)
public class CalendarData {
#JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "dd/MM/yyyy HH:mm:ss")
// field to contain formatted date as per clients requirement - shud be mirror of "date"
private String formattedDate;
private long date;
private String errorCode;
private String subErrorCode;
}
Downstream service is only sending date field as epoch and i want to have the formattedDate populated in run time in given format.
I can always write a custom function to format the data, but want to understand is there any native jackson way or custom setter to do that.

You're almost doing it right. However having a #JsonFormat-Annotation on a String field does not make to much sense, because if it already is String, there is nothing to convert for Jackson anymore. You can just make both fields of type Date and the #JsonFormat annotation on the formattedDate field will serialize it into the proper JSON String representation, exactly in the format you specified in the pattern. Jackson will by default serialize all java.util.Date Object of an object it needs to serialize into the epoch milliseconds as a regular JSON number. So this would work for you. However, as both fields in the final JSON will refer to the exact same Date object it feels weird to have them both as fields of the CalendarData object. I would suggest you just give CalendarData a single field date and then create a getter method for the formattedDate field. Here is what this could look like. By default Jackson will pick up all getter functions and serialize their returned data into the generated json object.
#Data
#JsonIgnoreProperties(ignoreUnknown = true)
public class CalendarData {
CalendarData(final Date date) {
this.date = date;
}
#JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "dd/MM/yyyy HH:mm:ss")
private Date getFormattedDate(){
return this.date;
};
private Date date;
}
UPDATE
As you updates you question I also want to update my answer. I recommend you the following (analogous to what I already explained above).
#Data
#Builder
#AllArgsConstructor
#NoArgsConstructor
#JsonIgnoreProperties(ignoreUnknown = true)
public class CalendarData {
private Date date;
private String errorCode;
private String subErrorCode;
#JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "dd/MM/yyyy HH:mm:ss")
// field to contain formatted date as per clients requirement - shud be mirror of "date"
private Date getFormattedDate(){
return this.date;
};
}
Then in my main I tried it out
public static void main(String[] args) throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
CalendarData data = CalendarData.builder()
.errorCode("23")
.subErrorCode("42")
.date(new Date())
.build();
System.out.println(mapper.writeValueAsString(data));
}
Which perfectly prints out
{
"date": 1676642216673,
"errorCode": "23",
"subErrorCode": "42",
"formattedDate": "17/02/2023 13:56:56"
}

Dealing with SimpleDateFormat passed in RequestBody

I'm developing a simple REST Controller. I'm receiving a SimpleDateFormat object in Request body. Looks like that:
2014-04-13T03:42:06-02:00
My current method now is:
#PostMapping
public ResponseEntity<Flight> addFlight(#RequestBody JSONObject object) {
Flight newFlight = new Flight(object.get("flightNumber").toString(), new
SimpleDateFormat ( object.get("departureDate").toString()));
repository.save(newFlight);
return ResponseEntity.status(HttpStatus.ACCEPTED).body(newFlight);
}
And class
#Data
#Entity
#DynamicUpdate
#NoArgsConstructor(access = AccessLevel.PRIVATE, force = true)
#RequiredArgsConstructor
#AllArgsConstructor
public class Flight {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;
private final String flightNumber;
private final SimpleDateFormat date;
}
Everything is compiling fine, but when I'm sending POST or GET I receive all of the data that I've passed, but SimpleDateFormat is null. How could I repair it?
I've also tried to pass Object to FlightClass and then use a converter in the class's constructor, but I've still had null.

SimpleDateFormat is a legacy class and i would recommend OffsetDateTime since your input represents ISO-8601 with offset
A date-time with an offset from UTC/Greenwich in the ISO-8601 calendar system, such as 2007-12-03T10:15:30+01:00.
OffsetDateTime dateTime = OffsetDateTime.parse(object.get("departureDate").toString());

Java LocalDate - Time gets appended onto date when saving in MongoDB?

I have the following Java Entity:
public class Round {
private ObjectId _id;
#NotEmpty
#Getter
#Setter
#Accessors(fluent = true)
#JsonProperty("userId")
private String userId;
#JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "dd-MM-yyyy")
#JsonDeserialize(using = LocalDateDeserializer.class)
#JsonSerialize(using = LocalDateSerializer.class)
#Getter
#Setter
#Accessors(fluent = true)
#JsonProperty("date")
private LocalDate date;
//other fields
}
When I do a POST to my Spring Boot REST web app with JSON Body:
{
"userId": "user3",
"date": "20-01-2020"
}
The date is persisted in Mongo as follows:
2020-01-20T00:00:00.000+00:00
How can I get the date to persist as simply:
20-01-2020

It's not Java problem, MongoDB uses Date format similar to JavaScript Date format.
If you want to save just dd-MM-YYYY you may want to change your column type to String.
If it's not possible then you need to rewrite your serializer to return String representation of date (and of course rewrite deserializer to parse that string into LocalDate

Constants for JsonFormat's pattern option

In our code we currently use the Jackson #JsonFormat annotation on a date object as follows:
#JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd'T'HH:mm:ssZZ")
private Date startDate;
Is there a class which defines constants for these patterns in order to avoid having such hardcoded value? Something like:
#JsonFormat(shape = JsonFormat.Shape.STRING, pattern = DateTimePatterns.ISO_DATETIME_TIMEZONE)
private Date startDate;
Or should I just create my own constants-class?

Java json response shows date in numeric value

#Data
public class Reponse {
private String event;
#Temporal(TemporalType.TIMESTAMP)
private Date eventDate;
private Double amount;
}
Json response is like
{
event: "transcation',
eventDate: 1213123434,
amount: 100
}
Here, eventDate is showing numeric value 1540317600000 instead of 2018-10-23

You can annotated the field with #JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd HH:mm"). Then, response time format will be like "yyyy-MM-dd HH:mm"
import com.fasterxml.jackson.annotation.JsonFormat;
public class Reponse {
private String event;
#Temporal(TemporalType.TIMESTAMP)
#JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd HH:mm")
private Date eventDate;
private Double amount;
}

If you use Spring boot 2.x instead 1.x ,the default behavior has changed
add spring.jackson.serialization.write-dates-as-timestamps=true to your configuration to return to the previous behavior
Spring Boot 2.0 Migration Guide

spring 2.x flipped a Jackson configuration default to write JSR-310 dates as ISO-8601 strings. If you wish to return to the previous behavior, you can add
spring.jackson.serialization.write-dates-as-timestamps=true
to your application-context configuration file.

I suppose you are using rest framework such as spring boot or jersey which in turn
converts your java date into epoch format before sending it to the client. So while
sending response you can format you date into the format you want. Please refer
the code below.
import java.text.SimpleDateFormat;
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.S");
sdf.setLenient(false);
String responseDate = sdf.format(date);