Serialize objects to a map with the object class as the key?-CodePudding

I'm writing a application using Spring boot and jackson for JSON parsing. I need to handle another service which produces JSON like this:

{
  "task-id": 5081,
  "task-created-on": {
    "java.util.Date": 1631022026000
  }
}

Notably, certain fields like the date field here are serialized into a map with a single key-value pair, where the key is a java classname and the value is the actual value of the field.

I've been going through the jackson documentation and haven't found anything about this format. Is there a way to configure jackson to produce and parse fields in this format?

At a minimum, I need to handle dates formatted this way. But I believe the service also uses this format for other objects, where the map key will be the name of some arbitrary java class and the value will be a map of its own. So I'd be interested in a solution that handles more than just dates if possible.

CodePudding user response：

It can be easily done with custom serializer in Jackson by following steps.
First, create objects for serialization as follows:

class MyDateObject {
    private Date date;

    //general getter/setter
}

class Task {
    @JsonProperty("task-id")
    private int taskId;

    @JsonProperty("task-created-on")
    private MyDateObject taskCreatedOn;

    //general getters/setters
}

Second, define your custom serializer: (Please note that I used myDateObject.getDate().getClass().getName() to get the class name of date field.)

class DateSerializer extends StdSerializer<MyDateObject> {
    public DateSerializer() {
        this(null);
    }

    protected DateSerializer(Class<MyDateObject> t) {
        super(t);
    }

    @Override
    public void serialize(MyDateObject myDateObject, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
        jsonGenerator.writeStartObject();
        jsonGenerator.writeNumberField(myDateObject.getDate().getClass().getName(), myDateObject.getDate().getTime());
        jsonGenerator.writeEndObject();
    }
}

Finally, register the serializer with ObjectMapper for the MyDateObject class and perform the serialization:

MyDateObject myDateObject = new MyDateObject();
myDateObject.setDate(new Date());

Task task = new Task();
task.setTaskId(5081);
task.setTaskCreatedOn(myDateObject);

SimpleModule simpleModule = new SimpleModule();
simpleModule.addSerializer(MyDateObject.class, new DateSerializer());

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.registerModule(simpleModule);

System.out.println(objectMapper.writeValueAsString(task));

The expected output is:

{"task-id":5081,"task-created-on":{"java.util.Date":1633402076254}}

Please refer to Jackson – Custom Serializer for more information.

CodePudding user response：

I did something like this, maybe it will work for you:

@Data
@AllArgsConstructor
@NoArgsConstructor
public class TaskRequest {

  @JsonProperty("task-id")
  private Long taskId;

  @JsonProperty("task-created-on")
  Map<String, Long> taskCreatedOn;
 }

@RestController
@RequestMapping("/test")
public class TestController {

@PostMapping
public void test(@RequestBody TaskRequest taskRequest) {
    taskRequest.getTaskCreatedOn().forEach((key, value) -> {
        try {
            Class<?> c = Class.forName(key);
            Constructor<?> cons = c.getConstructor(long.class);
            Object date = cons.newInstance(value);
            System.out.println(date);
        } catch (Exception e) {
            e.printStackTrace();
        }
    });
  }
}