Spring custom (de) serialization of date and time

Imagine a fairly common situation: your application interacts with clients that are in different time zones. You often have to work with dates, and for the system to work correctly, they are sent with the time zone of the sender. In doing so, you need:

1. When a request is received, bring the date to server time and work with it, and also save it to the database in this form

   
   
   
   
   

2. In response, return the date and time indicating the server time zone

   
   
   
   
   

To accomplish this, Spring provides a convenient mechanism for writing custom serialization and deserialization. Its main advantage is the ability to move date conversions (and other data types) into a separate configuration class and not call conversion methods every time in the source code.

Deserialization

In order for Spring to understand that it is our class that needs to be used for (de) serialization, it must be marked with the annotation @JsonComponent

Well, to keep the code as concise as possible, I will use an internal static class, which must be inherited from JsonDeserializer



and parameterized with the data type we need. Since it JsonDeserializer



 is an abstract class, we need to override its abstract methoddeserialize()

@JsonComponent
public class CustomDateSerializer {  
  
    public static class LocalDateTimeDeserializer extends JsonDeserializer<LocalDateTime> {
    
        @Override
        public LocalDateTime deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) {
            return null;
        }
    }
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

From the method parameters, we get the string passed by the client, check it for null and get a class object from it ZonedDateTime

public LocalDateTime deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) {
    String date = jsonParser.getText();
    if (date.isEmpty() || isNull(date) {
        return null;
    }
    ZonedDateTime userDateTime = ZonedDateTime.parse(date);
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, userDateTime



withZoneSameInstant()



. LocalDateTime

, , , . , .

public static class LocalDateTimeDeserializer extends JsonDeserializer<LocalDateTime> {

    @Override
    public LocalDateTime deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException {
        String date = jsonParser.getText();
        if (date.isEmpty()) {
            return null;
        }
        try {
            ZonedDateTime userDateTime = ZonedDateTime.parse(date);
            ZonedDateTime serverTime = userDateTime.withZoneSameInstant(ZoneId.systemDefault());
            return serverTime.toLocalDateTime();
        } catch (DateTimeParseException e) {
            try {
                return LocalDateTime.parse(date);
            } catch (DateTimeParseException ex) {
                throw new IllegalArgumentException("Error while parsing date", ex);
            }
        }
    }
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

,  UTC+03. , 2021-01-21T22:00:00+07:00



,

public class Subscription {

    private LocalDateTime startDate;
  
    // standart getters and setters
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

@RestController 
public class TestController {
  
  @PostMapping
  public void process(@RequestBody Subscription subscription) {
    //     startDate  subscription   2021-01-21T18:00
  }
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

. JsonSerializer



, serialize()

null, .

public static class LocalDateTimeSerializer extends JsonSerializer<LocalDateTime> {

    @Override
    public void serialize(LocalDateTime localDateTime, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
        if (isNull(localDateTime)) {
            return;
        }
        OffsetDateTime timeUtc = localDateTime.atOffset(ZoneOffset.systemDefault().getRules().getOffset(LocalDateTime.now()));
        jsonGenerator.writeString(timeUtc.toString());
    }
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

? ? . , , , UTC+00. , id . ZoneOffset

, UTC+03, : 2021-02-21T18:00+03:00.



UTC+00, 2021-02-21T18:00Z

Since we are working with a string, it will not be difficult for us to slightly change the code so that we always get the date in the same format at the output. Let's declare two constants - one of them will be equal to the default id UTC + 00, and the second - which we want to give to the client, and add a check - if the server time is in the zero time zone, then we will replace it Z



with +00:00



. As a result, our serializer will look like this

public static class LocalDateTimeSerializer extends JsonSerializer<LocalDateTime> {

    private static final String UTC_0_OFFSET_ID = "Z";
    private static final String UTC_0_TIMEZONE = "+00:00";

    @Override
    public void serialize(LocalDateTime localDateTime, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
        if (!isNull(localDateTime)) {
            String date;
            OffsetDateTime timeUtc = localDateTime.atOffset(ZoneOffset.systemDefault().getRules().getOffset(LocalDateTime.now()));
            if (UTC_0_OFFSET_ID.equals(timeUtc.getOffset().getId())) {
                date = timeUtc.toString().replace(UTC_0_OFFSET_ID, UTC_0_TIMEZONE);
            } else {
                date = timeUtc.toString();
            }
            jsonGenerator.writeString(date);
        }
    }
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Total

Thanks to the built-in spring mechanisms, we were able to automatically convert the date and time in the required format, without any explicit method calls in the code

The full source code can be viewed here