Dynamic polymorphic type handling with Jackson

Question

I have a class hierarchy similar to this one:

public static class BaseConfiguration {
}

public abstract class Base {
  private BaseConfiguration configurati         


        

Answer 1

I had to do something similar, and ended up creating a generic polymorphic list serializer and deserialzer. Here is the deserialize that I think will work for you:

    public class PolymorphicListDeserializer extends JsonDeserializer> implements ContextualDeserializer {
  private HashMap _typeMap = null;

  private Class _elementType;

  private static  List getNewList(Class clazz) {
    return new ArrayList();
  }

  @Override
  public List deserialize(final JsonParser jp, DeserializationContext ctxt) throws IOException {

    final List list = getNewList(_elementType);

    JsonToken nextToken = jp.getCurrentToken();

    if (nextToken == JsonToken.START_OBJECT) {
        if ( _typeMap.containsKey( currentFieldName )) {
          list.add( _elementType.cast( ctxt.readValue( jp, _typeMap.get( currentFieldName ) ) ) );
        }
        nextToken = jp.nextToken();
      } else if (currentFieldName != null && isEndToken(nextToken) && wrapperCount == 0) {
        break;
      } else {
        nextToken = jp.nextToken();
      }
    }
    return list;
  }

  public JsonDeserializer> createContextual( DeserializationContext ctxt, BeanProperty property ) throws JsonMappingException {
    //In Jackson 2.6.3, this method is called once per instance and the exception is never thrown
    if ( _typeMap == null )
      _typeMap = new HashMap();
    else
      throw new RuntimeException("Unsupported version of Jackson. Code assumes context is created once and only once.");

    _elementType = property.getType().getContentType().getRawClass();

    //For now, requiring XmlElements annotation to work.  May add support for JsonElements (if needed) later.
    for (XmlElement e : property.getAnnotation(XmlElements.class).value()) {
      _typeMap.put(e.name(), e.type());
    }

    return this;
  }

  private static boolean isStartToken(JsonToken t) {
    boolean result = false;
    if (t == JsonToken.START_OBJECT) {
      result = true;
    } else if (t == JsonToken.START_ARRAY) {
      result = true;
    }
    return result;
  }