Jackson : Make the most of POJO versus Immutable Objects

There is a simple dilemma that comes into my thoughts :
-> I have an object, right… class A { String b;int c}
-> It must be filled automatically thanks to unmarshalling from a json string {"b":"val1","c":2}
-> I want it to be immutable because I don’t want to alter my input, or to trust some insecure hashcode/equals methods.

Therefore : I must have a deserializable class, with final fields, a comprehensive constructor, and a builder pattern.

That sounds awkward with jackson. But is it possible ? Yes, it is, and I’ll prove it.

Neat, but let’s complicate this attempt a bit. Suppose we have a polymorphic object to be deserialized. It is a paradigmatic issue between Java and Json : Java is typed, Json does not care.
let’s declare this in pseudo DSL : class TripSegment { TransportMode mode; SegmentDetails detailsOfTheSegment }
and with several details classes like this one : class LocalTransitDetails implements SegmentDetails {String lineCode;DateTime timeOfDeparture;DateTime timeOfArrival;String departureStationName;String arrivalStationName;}

We want neither to create a TripSegmentBean as a POJO, nor to have a non jackson deserializer… So how to ?
Here is how I could successfully answer to that problem :

Now, I can handle my unmarshalled value object as if I built it manually. Now forget about dozer or BeanUtils. Let’s concentrate on the workflow.