Unwrapping object in custom serializer

[micsport13]

Due to some various factors and the complicated class structure I have, I need to use custom serialization rather than the default annotation based approach. I was wondering if there's any guides or specific methods I'm missing in order to unwrap a value within the object context. For context, here's my code:

public class ConstantValueGeneratorSerializer extends JsonSerializer<ConstantValueGenerator> {

  @Override
  public void serialize(
      ConstantValueGenerator constantValueGenerator,
      JsonGenerator jsonGenerator,
      SerializerProvider serializerProvider)
      throws IOException {
    String aliasName =
        Primitives.getAliasFromWrapperClass(constantValueGenerator.getConstantValue().getClass());
    Primitives primitives = Primitives.fromString(aliasName);
    jsonGenerator.writeObjectFieldStart("value");
    jsonGenerator.writeStringField("type", aliasName);
    jsonGenerator.writeFieldName("value"); // FIXME: Figure out how to unwrap this value
    switch (primitives) {
      case CUSTOM -> jsonGenerator.writeObject(constantValueGenerator.getConstantValue());
      case INT, DOUBLE, FLOAT, SHORT, BYTE, BOOLEAN, CHAR ->
          jsonGenerator.writeObject(
              Primitives.parseSimpleValueFromString(
                  primitives, constantValueGenerator.getConstantValue().toString()));
      default -> throw new IllegalArgumentException("Invalid primitive type");
    }
    jsonGenerator.writeEndObject();
  }

  @Override
  public void serializeWithType(
      ConstantValueGenerator value,
      JsonGenerator gen,
      SerializerProvider provider,
      TypeSerializer typeSerializer)
      throws IOException {
    WritableTypeId typeId = typeSerializer.typeId(value, JsonToken.START_OBJECT);
    typeSerializer.writeTypePrefix(gen, typeId);
    serialize(value, gen, provider);
    typeSerializer.writeTypeSuffix(gen, typeId);
  }

The problem arises on the jsonGenerator.writeObject(... line which works because I have wrapped the value by writing a field name but I was wondering, is it possible to unwrap that value and simply write the object within the value field name above?

It currently results in:

  value:
    type: custom
    value:
      class_name: java.time.Period
      method_name: of
      method_args:
        - type: int
          value: 0
        - type: int
          value: 0
        - type: int
          value: 1

but I would like

  value:
    type: custom
    class_name: java.time.Period
    method_name: of
    method_args:
      - type: int
        value: 0
      - type: int
        value: 0
      - type: int
        value: 1

Is this possible in a custom serializer?

[yawkat]

Get the serializer for the constant value from the context, then call unwrappingSerializer() on it to get a serializer that will just spit out the fields.

[micsport13]

Sorry, I'm not sure how to do that. Would I do that within the serialize method of the ConstantValueGeneratorSerializer? How do I obtain the constant value serializer within the ConstantValueGeneratorSerializer?

[cowtowncoder]

Yeah you cannot simply omit START_/END_OBJECT write: contract is such that by default serialize() call MUST result in a single JSON value; a set of key/value pairs isn't that. Exception is that "parent" serializer may ask for "unwrapping" serializer. But in your case you don't control the parent (only child serializer).
And it's parent serializer that writes field name.

So I am not sure this is achievable without custom parent serializer too.