1

I have pojo objects with inheritance and generics like this:

child object:

@Data
@ToString(callSuper = true)
@EqualsAndHashCode(callSuper = true)
public class MessageCreatedEvent extends AbstractEvent<MessageDto> {

    @JsonCreator
    public MessageCreatedEvent(MessageDto data) {
        super(data);
    }
}

parent:

@Data
public abstract class AbstractEvent<T> {

    private final UUID id = UUID.randomUUID();
    private T data;

    public AbstractEvent(T data) {
        this.data = data;
    }
}

and content holding object:

@Data
public class MessageDto implements Serializable {

    private UUID id;

    private String content;

    // and other fields
}

and jackson configuration which is used in rabbitTemplate:

@Bean
public MessageConverter jsonMessageConverter() {
    return new Jackson2JsonMessageConverter();
}

At start I didn't use @JsonCreator property but when I receive json message from RabbitMQ and tried it deserialize in rabbit handler I got this error:

Caused by: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of MessageCreatedEvent (no Creators, like default constructor, exist): cannot deserialize from Object value (no delegate- or property-based Creator)

After this I added @JsonCreator but then properties in MessageDto object are not set. There is only id field filled and others are null.

Can you tell me what I have wrong configured? Thank you.

EDIT:

I try modified pojos and remove generic data field from parent, and move it into child, now deserialization working, so it looks like that Jackson has som problem with generics. Any idea?

Denis Stephanov
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  • My guess is you have Jackson configured to use property getters/setters only. If you want to configure it to manipulate class member variables (aka fields) directly: https://stackoverflow.com/questions/7105745/how-to-specify-jackson-to-only-use-fields-preferably-globally – TrogDor Jul 23 '20 at 14:24
  • @TrogDor I found how to set it into Jackson2JsonMessageConverter which I am using but doesn't help – Denis Stephanov Jul 25 '20 at 16:17
  • @denis-stephanov, did you try the option below? – Kavithakaran Kanapathippillai Jul 27 '20 at 09:57
  • @denis-stephanov What do you mean with ‘I try modified pojos and remove generic data field from parent, and move it into child’? Can you explain it further to help understand the problem? – jccampanero Jul 27 '20 at 22:35
  • @JoséCarlosCampanero so I removed generics from parent and I add `data` field of required type to children – Denis Stephanov Jul 28 '20 at 19:17

2 Answers2

1
  • I copied your classes in a sample spring boot app (I am not using Lombok but replicating its behaviour) and doing the following and is working
    public class Testing {

      public static void main(String[] args) throws 
                  JsonProcessingException {
        ObjectMapper objectMapper = new ObjectMapper();
        MessageDto data = new MessageDto(UUID.randomUUID(), 
                                         "someContent");
        MessageCreatedEvent createdEvent = new MessageCreatedEvent();
        createdEvent.setData(data);
        String json = objectMapper.writeValueAsString(createdEvent);
        System.out.println(json);
        MessageCreatedEvent fromJson = 
            objectMapper.readValue(json, MessageCreatedEvent.class);
        System.out.println(fromJson.getData().getContent());
        System.out.println(fromJson.getData().getId());
      }
    }

  • Added a no argument constructor to MessageDto

  • Added a no argument constructor to AbstractEvent

  • Removed the following and is empty class:

      @JsonCreator
  public MessageCreatedEvent(MessageDto data) {
      super(data);
  }
Kavithakaran Kanapathippillai
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0

I'm not sure if it can help, but you may need to use @JsonProperty. To be more specific, please refer to https://thepracticaldeveloper.com/2016/10/23/produce-and-consume-json-messages-with-spring-boot-amqp/

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