How to change the data fomat of the JSON node while serializing and deserializing in jackson

Question

I have following Incoming json, which I deserialize to Model.java and then copy that java object to ModelView.java. I wan't to convert date from String to milliseconds and send the Outgoing json as response. How do I go for it ?

I've specific reason to copy the value from Model.java to ModelView.java using object mapper. So please don't suggest to modify that part. I'm looking to do this via annotation. I'm pretty sure that it can be done, but don't know how.

The json provided here is a simplistic one. I have a large json in actual scenario.

Incoming json

{
 "date":"2016-03-31"
}

Outgoing Json

{
 "date":236484625196
}

My Controller Class

@Controller
public class SomeController extends BaseController {

    @Autowired
    private SomeService someService;


    @RequestMapping(method = RequestMethod.GET, produces = "application/json")
    public @ResponseBody
    ResponseEntity<RestResponse> getDetails(HttpServletRequest request, HttpServletResponse response) {

        Model model = someService.getData();

        ModelView modelView = ModelView.valueOf(model);

        return getSuccessResponse(modelView);
    }
}

Model.java

@JsonInclude(Include.NON_NULL)
@JsonIgnoreProperties(ignoreUnknown = true)
public class Model implements Serializable {

    private String date;

    //normal getters and setters
}

ModelView.java

@JsonInclude(Include.NON_NULL)
@JsonIgnoreProperties(ignoreUnknown = true)
public class ModelView implements Serializable {

    private Long date;
    //normal getters and setters


    public static ModelView valueOf(Model model){
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-mm-dd");

        ObjectMapper mapper = new ObjectMapper();
        ModelView modelView =  mapper.convertValue(model, ModelView.class);
        try {

            modelView.setDate(sdf.parse(model.getDate()).getTime());
        } catch (ParseException e) {
            IntLogger.error("logging error here");
        }
        return modelView;
    }
}

I'm open to change the variable name from "date" to something else in ModelView.java but the outgoing json should remain same.

Answer 1

Jackson has some build in date formatting, for example, you can set the DateFormatter on the object mapper, but i believe this only works if the serialization and deserialization format is the same.

A simpler approach to date serialization and deserialization, if you want serialization and deserialization to be different format, is to use @JsonSerialize and @JsonDeserialize annotations on your Model.class directly (this could obsolete the need for ModelView if your only purpose was to convert the date).

You can create two classes for serialization and deserialization:

public class JsonDateDeserializer extends JsonDeserializer<Date> {

    @Override
    public Date deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException, JsonProcessingException {
        final SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
        String dateString = jsonParser.getText();
        try {
            return dateFormat.parse(dateString);
        }
        catch (ParseException e) {
            throw new RuntimeException(e);
        }
    }
}

Then for the serialization to your Outgoing json:

public class JsonDateSerializer extends JsonSerializer<Date> {

    @Override
    public void serialize(Date date, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, JsonProcessingException {
        jsonGenerator.writeString(Long.toString(date.getTime()));

    }
}

Now, you an just annotate your Model.java:

@JsonInclude(Include.NON_NULL)
@JsonIgnoreProperties(ignoreUnknown = true)
public class Model implements Serializable {

    @JsonSerialize(using = JsonDateSerializer.class)
    @JsonDeserialize(using = JsonDateDeserializer.class)
    private String date;

    //normal getters and setters
}