How to serialize an instant without nanoseconds using spring boot with jackson?

To serialize an Instant object without nanoseconds using Spring Boot with Jackson, you can use the following steps:

Configure the ObjectMapper bean to use the JavaTimeModule:

@Bean
public ObjectMapper objectMapper() {
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.registerModule(new JavaTimeModule());
return objectMapper;
}

Use the @JsonFormat annotation to specify the format of the Instant object:

public class MyDto {
@JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd'T'HH:mm:ss'Z'", timezone = "UTC")
private Instant date;

// Getters and setters for date
}

When serializing the Instant object, it will now be formatted as a string in the specified pattern, without the nanoseconds.

MyDto dto = new MyDto();
dto.setDate(Instant.now());

String json = objectMapper.writeValueAsString(dto);

This will produce a JSON string like the following:

{"date":"2022-12-23T00:00:00Z"}

Note that the JavaTimeModule also provides additional customization options for serializing and deserializing other Java 8 date and time types, such as LocalDate, LocalTime, etc. You can read more about these options in the Jackson documentation.