@JsonDeserialize(builder = ) without annotations

Question

I would like to deserialize an immutable class which is defined in a dependency, and therefore I cannot modify. It only has a private constructor, and has to be built using a builder.

With Jackson it's possible to use @JsonDeserialize(builder = SomeClass.SomeClassBuilder.class) to deserialize such an object. Unfortunately, I cannot add the annotation.

Is it possible to register such a builder without using annotations, and if it is, how would you go about and do it?

Write your custom deserializer where inside use builder to build the object of class and use deserializer in @JsonDeserialize — Eklavya, Aug 11 '20 at 08:17
OK, but is there a way to do it without a custom deserializer? — Ynv, Aug 11 '20 at 08:24
@TraychoIvanov it's code provided by a dependency (an external library) — Ynv, Aug 11 '20 at 12:53
@Ynv You could extend the class and put annotation in your class or create a new deserialiser using `JsonDeserializer`. — Traycho Ivanov, Aug 11 '20 at 13:44

score 1 · Answer 1 · answered Aug 11 '20 at 08:18

You might want to have a look at the examples here (first hit on google BTW):

Define a custom Deserializer:

public class SomeClassDeserializer extends StdDeserializer<SomeClass> { 
 
    public SomeClassDeserializer() { 
        this(null); 
    } 
 
    public SomeClassDeserializer(Class<?> vc) { 
        super(vc); 
    }
 
    @Override
    public SomeClass deserialize(JsonParser jp, DeserializationContext ctxt) 
      throws IOException, JsonProcessingException {
        JsonNode node = jp.getCodec().readTree(jp);
        // read values from node and use the SomeClassBuilder
        // to create an instance of SomeClass
    }
}

Make Jackson aware of the deserializer by registering it with an ObjectMapper:

ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addDeserializer(SomeClass.class, new SomeClassDeserializer());
mapper.registerModule(module);
 
SomeClass readValue = mapper.readValue(json, SomeClass.class);

Depending on the framework you're using there might be other more elegant ways to register the deserializer.

Thanks. I was wondering whether it's possible to do without a custom deserialzer? — Ynv, Aug 11 '20 at 08:25
I doubt this is possible. You would probably need to add some annotation on the builder as well to make Jackson know what to do with it. https://stackoverflow.com/questions/4982340/jackson-builder-pattern — dpr, Aug 11 '20 at 08:30
@Ynv Pretty much options are using the annotation or extend `JsonDeserializer`, this is how jackon will be notified you plan to use custom deserialisation. — Traycho Ivanov, Aug 11 '20 at 10:50

@JsonDeserialize(builder = ) without annotations

1 Answers1