Jackson JSON Processor

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.4.2
• Fix Version/s: 1.5
• Component/s: JSON tree (JsonNode)
• Labels:

  None
• Environment:

  Jackson 1.4.2

Hello Jackson team !

First, thank you for creating this fast Json processing framework. I recently switched from Gson to Jackson on an Android project and the results outperform my expectations (Gson creates tons of temporary objects, and Android GC sucks).

One thing I enjoy with Gson is to be able to serialize/deserialize entities without no fwk specific configuration. I can create pojos with private fields + getters, a private constructor and no setters, and Gson is able to deserialize my entities from Json.

Jackson however requires the fields to either be public, have a specific annotation (@JsonProperty), or have the corresponding setter.

Just to be clear : I'd like to be able to serialize / deserialize such a class :

public class MyBean {
private String name;

public String getName() { return name; }
}

It would be nice if there was an option, disabled as default, to allow private fields with no annotation to be auto detected. Something like (De)SerializationConfig.Feature.AUTO_DETECT_PRIVATE_FIELDS

I only looked at Deserialization for now since it's what I need. I think the main changes would occur in BasicBeanDescription._findPropertyFields (l 762) :

if (!autodetect || !af.isPublic()) { continue; }

=> would become something like

if (!autodetect || (!af.isPublic() && !autodetect_private_fields)) { continue; } }

This feature would be nice for prototyping, and quickly being able to parse Json. It would also help migrating from Gson.

I managed to enable this feature when deserializing Json with Jackson 1.4.2, but the code is dirty... here is what I did anyway :

• Create a subclass of BasicBeanDescription that overrides _findPropertyFields to remove the isPublic check.
• Create a subclass of BasicClassIntrospector that overrides forDeserialization method and return my custom BasicBeanDescription instead of a standard BasicBeanDescription.
• Create an instance of DeserializationConfig injected with the custom BasicClassIntrospector, and inject it in the ObjectMapper.

Here is the ugly code :

ObjectMapper om = new ObjectMapper();

BasicClassIntrospector bci = new BasicClassIntrospector() {
@Override
public BasicBeanDescription forDeserialization(DeserializationConfig cfg, JavaType type,
org.codehaus.jackson.map.ClassIntrospector.MixInResolver r) {
final AnnotationIntrospector ai = cfg.getAnnotationIntrospector();
final AnnotatedClass ac = AnnotatedClass.construct(type.getRawClass(), ai, r);
// everything needed for deserialization, including ignored
// methods
ac.resolveMemberMethods(getDeserializationMethodFilter(cfg), true);
// include all kinds of creator methods:
ac.resolveCreators(true);
// yes, we need info on ignored fields as well
ac.resolveFields(true);
return new BasicBeanDescription(type, ac, ai) {

@Override
public LinkedHashMap<String, AnnotatedField> _findPropertyFields(boolean autodetect,
Collection<String> ignoredProperties, boolean forSerialization) {
Boolean classAD = ai.findFieldAutoDetection(ac);
if (classAD != null) { autodetect = classAD.booleanValue(); }

LinkedHashMap<String, AnnotatedField> results = new LinkedHashMap<String, AnnotatedField>();
for (AnnotatedField af : ac.fields()) {
/*

• note: some prefiltering has been; no static or
• transient fields included; nor anything marked as
• ignorable (@JsonIgnore)
  */

/*

• So far so good: final check, then; has to either
• (a) be marked with JsonProperty (or
• JsonSerialize) OR (b) be public
  */
  String propName = forSerialization ? ai.findSerializablePropertyName(af) : ai
  .findDeserializablePropertyName(af);
  if (propName != null)
  Unknown macro: { if (propName.length() == 0) { propName = af.getName(); } }
  else
  Unknown macro: { // nope, but is a public field? // ****** MY CHANGE }
  
  }

/*

• Yup, it is a valid name. But do we have a
• conflict? Shouldn't usually happen, but it is
• possible... and for now let's consider it a
• problem
  */
  AnnotatedField old = results.put(propName, af);
  if (old != null) { String oldDesc = old.getFullName(); String newDesc = af.getFullName(); throw new IllegalArgumentException("Multiple fields representing property \"" + propName + "\": " + oldDesc + " vs " + newDesc); }
  }
  return results;
  }

};
}
};

DeserializationConfig deserConfig = new DeserializationConfig(bci, new JacksonAnnotationIntrospector());

om.setDeserializationConfig(deserConfig);

om.configure(DeserializationConfig.Feature.AUTO_DETECT_FIELDS, true);
om.configure(DeserializationConfig.Feature.CAN_OVERRIDE_ACCESS_MODIFIERS, true);

If you find any cleaner way, please let me know !

• Assignee:

  Tatu Saloranta

  Reporter:

  Pierre-Yves Ricau

• Created:

  19/Feb/10 7:43 AM

  Updated:

  01/Jun/10 11:32 AM

  Resolved:

  09/Mar/10 12:56 AM