杰克逊的@JsonPropertyOrder 不适用于@JsonUnwrapped

Question

I have an object that contains another object attribute like this:

import com.fasterxml.jackson.annotation.JsonPropertyOrder;
import com.fasterxml.jackson.annotation.JsonUnwrapped;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import lombok.Data;

@JsonPropertyOrder({"fA1","b","fA2"})
@Data
public class A {
    private String fA1;
    private String fA2;

    @JsonUnwrapped
    private B b = new B();

    @Data
    class B {
        private String fB1;
        private String fB2;
    }

    public static void main(String[] args) throws JsonProcessingException {
        ObjectMapper objectMapper = new ObjectMapper();
        A a = new A ();
        System.out.println(objectMapper.writeValueAsString(a));
    }

}

what i want is generate json that respect this order:

{
  "fA1":"",
  "fB1":"",
  "fA2":"",
  "fB2":""
}

Is there any way to do this?

Answer 1

According to this issue in the jackson-databind repository on GitHub, the @JsonPropertyOrder annotation doesn't work with @JsonUnwrapped annotation. See the quote below:

True, unwrapped properties are not included in ordering, since they are not really known by enclosing serializer as regular properties. And specifically, as things are, will be output as a block of properties per contained, so even if known they can not be reordered separately.

Perhaps something could be done with Jackson 3.x once we get there.

---

But you may consider a workaround : as you seem to be using Lombok, you could annotate b with @Delegate and @JsonIgnore :

@Data
@JsonPropertyOrder({"fa1", "fb1", "fa2", "fb2"})
public class A {

    private String fA1;
    private String fA2;

    @Delegate
    @JsonIgnore
    private B b = new B();
}

The @JsonIgnore annotation will ensure that the b property is not serialized by Jackson.

And the @Delegate annotation will tell Lombok to generate delegate methods that forward the call to the B methods. With that, the A class will have getters and setters that are delegated to the getters and setters of the fB1 and fB2 fields.