Question

i’m using hibernate to lazily retrieve content from a database.
This content is then serialised to json output, the problem is that jackson invoke getters on the “persistentBag” i get from hibernate, ending with a “no session or session was closed” exception.

In fact i would like to tell jackson “if a list is not loaded (means if it’s a persistentBag) then don’t serialise it”

What is the best way to achieve this ? Any jackson config to excluse persistentBag from serialisation ?
Should i use reflect api to set persistentBag to new empty list ?

What’s the best ? Thank you and happy new year guys !

Answer 1

You could try to use @JsonIgnore to entirely ignore the marked property. Annotation wise I don’t think there is a “if lodaded” option.

What you could of course do is to write your own marshaller that checks the type and decides how to proceed.

I have e.g. written a serializer for a custom data type

public class PropertyValueSerializer extends JsonSerializer<PROPERTY_VALUE> {

    @Override
    public void serialize(PROPERTY_VALUE property_value, JsonGenerator jsonGenerator,
                          SerializerProvider serializerProvider) throws IOException, JsonProcessingException {

        jsonGenerator.writeStartObject();
        jsonGenerator.writeFieldName(property_value.getKey());
        jsonGenerator.writeString(property_value.getValue());
        jsonGenerator.writeEndObject();
    }
}

Which is then used to serialize that type by adding some annotations:

@JsonSerialize(using = PropertyValueSerializer.class)
@JsonDeserialize(using = PropertyValueDeserializer.class)
public class PROPERTY_VALUE implements Serializable{

    private String key;
    private String value;

That custom serializer gives you full control, but is of course a bit more work to implement than just a simple annotation.