How to apply jackson's default behaviour in custom serializer? - jackson-databind

Question

Since Jackson's hibernate5-module not working for me. I'm trying to implement my own lazy property filter. I implemented custom annotation introspection successfully.
But when I apply my custom serializer, #JsonIgnoreProperties is ignored.
#Entity
class Call {
#OneToMany(mappedBy = "call")
#JsonIgnoreProperties("call")
List<CallEvent> events;
}
#Entity
class CallEvent {
#ManyToOne(fetch = FetchType.LAZY)
Call call;
}
public class LazyValueIntrospector extends JacksonAnnotationIntrospector {
#Override
public Object findSerializer(Annotated a) {
var yes = a.hasAnnotation(ManyToOne.class)
|| a.hasAnnotation(Basic.class)
|| a.hasAnnotation(OneToMany.class)
|| a.hasAnnotation(OneToOne.class);
if (yes) {
return LazyValueSerializer.class;
}
return super.findSerializer(a);
}
}
public class LazyValueSerializer extends JsonSerializer<Object> {
#Override
public boolean isEmpty(SerializerProvider provider, Object value) {
return value == null || !Hibernate.isInitialized(value);
}
#Override
public void serialize(Object value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
gen.writeObject(value);
}
}
Explanation:
LazyValueIntrospector.findSerializer detects possible lazy properties.
Hibernate.isInitialized tells me the value is initialized or not.
gen.writeObject(value); writes if property is initialized.
The problem is gen.writeObject(value); method call is ignoring #JsonIgnoreProperties("call") annotation.
The question is:
How to apply #JsonIgnoreProperties("call") annotation in my custom serializer?
Ps: spring.jackson.defaultPropertyInclusion=non_empty property applied globally. Which allows isEmpty checking.

Answer 1

As we are ignoring only one property, try giving #JsonIgnore over the call property inside the CallEvent entity above Call.
Example:
#Entity
class CallEvent {
#ManyToOne(fetch = FetchType.LAZY)
#JsonIgnore
Call call;
}

Answer 2

Without actual example of where #JsonIgnoreProperties is ignored it is hard to say. But I think that the custom serializer would need to delegate to the original serializer and not replace it; there's quite a bit more that is needed to support various other features.
To do that you cannot register serializer the way like shown here, but instead replace it using one of methods in BeanSerializerModifier (and need to register that modifier with ObjectMapper) -- that way you get the "real" serializer to delegate to.
Usually implementations also need to implement createContextual() (from ContextSerializer) which needs to be passed to the original ("delegate") serializer.
You may want to have a look at how serializers are implemented in Hibernate module itself.

Answer 3

So, Since the question is how to apply jackson's own behaviors in the custom bean serializer. I found the answer for myself.
extend from BeanSerializerBase, not BeanSerializer.
override with* methods. Such as withByNameInclusion and withProperties
This way, Jackson calls appropriate methods when it's needed.
#Override
public JsonSerializer<Object> unwrappingSerializer(NameTransformer unwrapper) {
return new LazyBeanUnwrappingSerializer(this, unwrapper);
}
#Override
protected BeanSerializerBase withProperties(BeanPropertyWriter[] properties, BeanPropertyWriter[] filteredProperties) {
return new LazyBeanSerializer(this, properties, filteredProperties);
}
#Override
protected BeanSerializerBase withByNameInclusion(Set<String> toIgnore, Set<String> toInclude) {
return new LazyBeanSerializer(this, toIgnore, toInclude);
}
#Override
public BeanSerializerBase withObjectIdWriter(ObjectIdWriter objectIdWriter) {
return new LazyBeanSerializer(this, objectIdWriter, _propertyFilterId);
}
#Override
public BeanSerializerBase withFilterId(Object filterId) {
return new LazyBeanSerializer(this, _objectIdWriter, filterId);
}
#Override
protected BeanSerializerBase asArraySerializer() {
throw new RuntimeException("Array serializer no supported");
}