Create a full keymap from Jackson annotated java Classes

I need to create a json structure with all possible keys from a given jackson annotated java class.

Example java class looks like this:

public class Data {

   private FieldA fieldA;
   private String fieldB;

   public FieldA fieldA(FieldA fieldA) {
       this.fieldA = fieldA;
       return this;
   }

   @JsonProperty("fieldA")
   @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
   public void setFieldA(FieldA fieldA) {
       this.fieldA = fieldA;
   }
   
   public String fieldB(String fieldB) {
       this.fieldB = fieldB;
       return this;
   }

   @JsonProperty("fieldB")
   @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
   public void setFieldB(String fieldB) {
       this.fieldB = fieldB;
   }
}

public class FieldA {
   private String moreData1;
   private String moreData2;
   
   public String moreData1(String moreData1) {
       this.moreData1 = moreData1;
       return this;
   }

   @JsonProperty("moreData1")
   @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
   public void setMoreData(String moreData1) {
       this.moreData1 = moreData1;
   }
   
   public String moreData2(String moreData2) {
       this.moreData2 = moreData2;
       return this;
   }

   @JsonProperty("moreData2")
   @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
   public void setMoreData(String moreData2) {
       this.moreData2 = moreData2;
   }
}

The problem is that the container class “data” has many fields, which in turn have many fields again.

There are some conditions which makes it maybe possible.

• All java classes behave like standard pojos. They all have default a constructor.

• The last Field which have no further fields can be null. (json values can be null)

• All Java classes and its fields are jackson annotated

Goal should look like this:

{
    "fieldA" : {
        "moreData1" : null
        "moreData2" : null
    },
    "fieldB" : null
}

Like a template of the full json model where only “the last” values are missing.

How can this be achieved or is there already a solution out there?

I tryed already with:

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.setSerializationInclusion(JsonInclude.Include.ALWAYS);
objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);

String json = objectMapper.writeValueAsString(new Data());

but this creates only the structure actual given class and its fields and doesn’t go deeper into fields (like it possibly could with default construction)