JSOG support without the need to annotate the classes

[donshop11]

is it possible to make JSOG work without annotating the class hierarchy?

I have a class hierarchy which I do not control and need to serialize into JSON, unfortunately it has cyclic references. I understand it requires some book keeping (checking for each object if it was already referenced) , but sometimes it can be the only way to use JSOG.

[stickfigure]

This is really a question for Tatu on the Jackson mailing list. FWIW, I'd like to know the answer myself. I'll ask and report back.

[stickfigure]

Tatu says:

Yes, as with all Annotation-backed configuration, implementing AnnotationIntrospector (either sub-classing JacksonAnnotationIntrospector or NopAnnotationIntrospector), registering it with ObjectMapper allows use of alternative configuration sources.

There is no in-built equivalent of "default typing", although theoretically similar system could be added for object identity handling as well, if that seems like a good idea.

I'm turning this into a feature request to add an AnnotationIntrospector that enables this behavior.

[edobry]

👍 , would love to see this implemented, or alternatively some direction on how I could do it myself

[stickfigure]

Unfortunately my Jackson-fu is inadequate, but we'll keep this open until somebody figures it out.

[cjalmeida]

I didn't test it but you could create a "Mixin" class with the JsonIdentityInfo annotation. See:

http://wiki.fasterxml.com/JacksonMixInAnnotations

You can even set the mixin to be applied to all classes:

objectMapper.getSerializationConfig().addMixInAnnotations(Object.class, JSOGMixin.class);
objectMapper.getDeserializationConfig().addMixInAnnotations(Object.class, JSOGMixin.class);

(BTW the ObjectMapper was meant to be created once and shared across the application)

[cjalmeida]

BTW, I did test and works as charm!

Create a simple class as mixin:

@JsonIdentityInfo(generator = JSOGGenerator.class)
public static class JSOGMixin {

}

Then create a SimpleModule and append to your ObjectMapper

SimpleModule jModule = new SimpleModule();
jModule.setMixInAnnotation(Object.class, JSOGMixin.class);

[fsparv]

I'm having some difficulty round tripping using the SimpleModule approach... when I try

mapper.registerModule(jModule);
String json = mapper.writeValueAsString(t);
mapper.readValue(json, Thing.class);

I get

com.fasterxml.jackson.databind.JsonMappingException: Unexpected token (VALUE_STRING), expected START_ARRAY: need JSON Array to contain As.WRAPPER_ARRAY type information for class com.voodoodyne.jackson.jsog.JSOGRef
at [Source: [ "com.foo.model.Thing", {
  "@id" : "1",
  "name" : "foo",
  "date" : [ "java.util.Date", 1493408755084 ]
} ]; line: 2, column: 11] (through reference chain: com.foo.model.Thing["@id"])
	at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:216)
	at com.fasterxml.jackson.databind.DeserializationContext.wrongTokenException(DeserializationContext.java:962)
	at com.fasterxml.jackson.databind.jsontype.impl.AsArrayTypeDeserializer._locateTypeId(AsArrayTypeDeserializer.java:127)
	at com.fasterxml.jackson.databind.jsontype.impl.AsArrayTypeDeserializer._deserialize(AsArrayTypeDeserializer.java:93)
	at com.fasterxml.jackson.databind.jsontype.impl.AsArrayTypeDeserializer.deserializeTypedFromAny(AsArrayTypeDeserializer.java:68)
	at com.fasterxml.jackson.databind.JsonDeserializer.deserializeWithType(JsonDeserializer.java:149)
	at com.fasterxml.jackson.databind.deser.impl.TypeWrappedDeserializer.deserialize(TypeWrappedDeserializer.java:42)
	at com.fasterxml.jackson.databind.deser.impl.ObjectIdValueProperty.deserializeSetAndReturn(ObjectIdValueProperty.java:79)
	at com.fasterxml.jackson.databind.deser.impl.ObjectIdValueProperty.deserializeAndSet(ObjectIdValueProperty.java:71)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:341)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeWithObjectId(BeanDeserializerBase.java:1094)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:131)
	at com.fasterxml.jackson.databind.jsontype.impl.AsArrayTypeDeserializer._deserialize(AsArrayTypeDeserializer.java:110)
	at com.fasterxml.jackson.databind.jsontype.impl.AsArrayTypeDeserializer.deserializeTypedFromObject(AsArrayTypeDeserializer.java:58)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeWithType(BeanDeserializerBase.java:1017)
	at com.fasterxml.jackson.databind.deser.impl.TypeWrappedDeserializer.deserialize(TypeWrappedDeserializer.java:42)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3788)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2779)
	at com.fasterxml.jackson.databind.ObjectMapper$readValue$2.call(Unknown Source)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
	
<SNIP intellij groovy console classes>

Same result for

mapper.addMixIn(Object.class, JSOGMixin.class);

Class is like this:

package com.foo.model;
import java.util.Date;

public class Thing {
  public String name;
  public Date date;

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public Date getDate() {
    return date;
  }

  public void setDate(Date date) {
    this.date = date;
  }
}

This was with Jackson 2.5.1 and 2.7.0. I checked out the code from this project and wrote this in unit test form and got a different exception due to 2.5.0 dep in your pom:

java.lang.IllegalArgumentException: Invalid type id 'com.voodoodyne.jackson.jsog.Thing' (for id type 'Id.class'): Class com.voodoodyne.jackson.jsog.Thing is not assignable to com.voodoodyne.jackson.jsog.JSOGRef

	at com.fasterxml.jackson.databind.jsontype.impl.ClassNameIdResolver._typeFromId(ClassNameIdResolver.java:68)
	at com.fasterxml.jackson.databind.jsontype.impl.ClassNameIdResolver.typeFromId(ClassNameIdResolver.java:48)
	at com.fasterxml.jackson.databind.jsontype.impl.TypeDeserializerBase._findDeserializer(TypeDeserializerBase.java:157)
	at com.fasterxml.jackson.databind.jsontype.impl.AsArrayTypeDeserializer._deserialize(AsArrayTypeDeserializer.java:94)
	at com.fasterxml.jackson.databind.jsontype.impl.AsArrayTypeDeserializer.deserializeTypedFromAny(AsArrayTypeDeserializer.java:68)
	at com.fasterxml.jackson.databind.JsonDeserializer.deserializeWithType(JsonDeserializer.java:151)
	at com.fasterxml.jackson.databind.deser.impl.TypeWrappedDeserializer.deserialize(TypeWrappedDeserializer.java:42)
	at com.fasterxml.jackson.databind.deser.impl.ObjectIdReader.readObjectReference(ObjectIdReader.java:136)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectId(BeanDeserializerBase.java:1045)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeWithType(BeanDeserializerBase.java:953)
	at com.fasterxml.jackson.databind.deser.impl.TypeWrappedDeserializer.deserialize(TypeWrappedDeserializer.java:42)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3560)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2576)
	at com.voodoodyne.jackson.jsog.issue5WorkaroundTest.testIssue5Workaround(issue5WorkaroundTest.java:29)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)

<SNIP junit classes>

Caused by: java.lang.IllegalArgumentException: Class com.voodoodyne.jackson.jsog.Thing is not assignable to com.voodoodyne.jackson.jsog.JSOGRef
	at com.fasterxml.jackson.databind.JavaType._assertSubclass(JavaType.java:439)
	at com.fasterxml.jackson.databind.JavaType.narrowBy(JavaType.java:149)
	at com.fasterxml.jackson.databind.type.TypeFactory.constructSpecializedType(TypeFactory.java:221)
	at com.fasterxml.jackson.databind.jsontype.impl.ClassNameIdResolver._typeFromId(ClassNameIdResolver.java:64)
	... 40 more

[fsparv]

Ah ha.. my simple case above succeeds if I remove

mapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL)

which I had previously added to handle abstract types (in more complicated code for actual use), so it seems that the workaround by @cjalmeida only stumbles if one is trying to use this technique to handle abstract types

[chaoyangnz]

Please prioritize this. For some classes in 3rd party library, we cannot add annotations, we just need to serialize to JSON.

Thanks

[stickfigure]

@chaoyangnz what's wrong with using jackson mixins? That's the natural jackson solution to "I can't annotate my classes".

[chaoyangnz]

@stickfigure

I have a Integer field in my pojo, I applied the mixin, and I got an exception:

java.lang.Integer cannot be cast to com.voodoodyne.jackson.jsog.JSOGRef

I will isolate the issue and provide you the example shortly.