Strange Jackson exception being thrown when serializing Hibernate object

Question

Jackson is throwing a weird exception that I don't know how to fix. I'm using Spring, Hibernate and Jackson.

I have already considered that lazy-loading is causing the problem, but I have taken measures to tell Jackson to NOT process various properties as follows:

@JsonIgnoreProperties({ "sentMessages", "receivedMessages", "educationFacility" })
public class Director extends UserAccount implements EducationFacilityUser {
   ....
}

I have done the same thing for all the other UserAccount subclasses as well.

Here's the exception being thrown:

org.codehaus.jackson.map.JsonMappingException: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: java.util.ArrayList[46]->jobprep.domain.educationfacility.Director_$$_javassist_2["handler"])
    at org.codehaus.jackson.map.ser.StdSerializerProvider$1.serialize(StdSerializerProvider.java:62)
    at org.codehaus.jackson.map.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:268)
    at org.codehaus.jackson.map.ser.BeanSerializer.serializeFields(BeanSerializer.java:146)
    at org.codehaus.jackson.map.ser.BeanSerializer.serialize(BeanSerializer.java:118)
    at org.codehaus.jackson.map.ser.ContainerSerializers$IndexedListSerializer.serializeContents(ContainerSerializers.java:236)
    at org.codehaus.jackson.map.ser.ContainerSerializers$IndexedListSerializer.serializeContents(ContainerSerializers.java:189)
    at org.codehaus.jackson.map.ser.ContainerSerializers$AsArraySerializer.serialize(ContainerSerializers.java:111)
    at org.codehaus.jackson.map.ser.StdSerializerProvider._serializeValue(StdSerializerProvider.java:296)
    at org.codehaus.jackson.map.ser.StdSerializerProvider.serializeValue(StdSerializerProvider.java:224)
    at org.codehaus.jackson.map.ObjectMapper.writeValue(ObjectMapper.java:925)
    at org.springframework.http.converter.json.MappingJacksonHttpMessageConverter.writeInternal(MappingJacksonHttpMessageConverter.java:153)

Suggestions on how I can get more info to see what's causing this? Anyone know how to fix it?

EDIT: I discovered that getHander() and other get*() methods exist on the proxy object. GRR!! Is there any way I can tell Jackson to not process anything on the proxy, or am I sol? This is really weird because the method that spits out the JSON only crashes under certain circumstances, not all the time. Nonetheless, it's due to the get*() methods on the proxy object.

Aside: Proxies are evil. They disrupt Jackson, equals() and many other parts of regular Java programming. I am tempted to ditch Hibernate altogether :/

Answer 1

I had a similar problem with lazy loading via the hibernate proxy object. Got around it by annotating the class having lazyloaded private properties with:

@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})

I assume you can add the properties on your proxy object that breaks the JSON serialization to that annotation.

Avoid Jackson serialization on non fetched lazy objects

Answer 2

It's not ideal, but you could disable Jackson's auto-discovery of JSON properties, using @JsonAutoDetect at the class level. This would prevent it from trying to handle the Javassist stuff (and failing).

This means that you then have to annotate each getter manually (with @JsonProperty), but that's not necessarily a bad thing, since it keeps things explicit.