Jackson deserialization: Can I inject a value with an annotation on the field of the to deserializable object?

Question

I have an object like this to deserialize:

public class RelationsInput {

   Relation relation1;

   Relation relation2;

}

whereas the class Relation looks like this:

public class Relation {

   RelationType relationtype;
   ... (more fields)

}

RelationType is en enum and is not a value which will be deserialized, while all others are.

Is it possible, that I could "inject" the enum value for the field relationType with an annotation on the field in the class RelationInput? Like the following


public class RelationsInput {

   @RelationType(RelationType.OWNER)
   Relation owner;

   @RelationType(RelationType.TENANT)
   Relation tenant;

}

Does Jackson provide something like this?

Why wont the relationType field be serialized/deserialized? This might help you understand enums and serialization better https://www.baeldung.com/jackson-serialize-enums — JCompetence, Nov 24 '20 at 12:45
The field is not contained in the serialized data. It's a context information of the `RelationsInput` class. — Herr Derb, Nov 24 '20 at 13:27

score 2 · Accepted Answer · answered Nov 25 '20 at 00:04

You can try to implement custom deserialiser with com.fasterxml.jackson.databind.deser.ContextualDeserializer interface. It allows to create deserialiser instance with a context.

See below example:

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.BeanProperty;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.deser.ContextualDeserializer;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import com.fasterxml.jackson.databind.json.JsonMapper;
import lombok.Data;

import java.io.File;
import java.io.IOException;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

public class JsonContextualDeserializerApp {
    public static void main(String[] args) throws IOException {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        ObjectMapper mapper = JsonMapper.builder().build();
        RelationsInput info = mapper.readValue(jsonFile, RelationsInput.class);

        System.out.println(info.toString());
    }
}

@Data
class RelationsInput {

    @JsonDeserialize(using = RelationStdDeserializer.class)
    @RelationTypeInfo(RelationType.OWNER)
    private Relation owner;

    @JsonDeserialize(using = RelationStdDeserializer.class)
    @RelationTypeInfo(RelationType.TENANT)
    private Relation tenant;

}

@Data
class Relation {

    private int id;
    private RelationType relationtype;
}

enum RelationType {OWNER, TENANT}

@Retention(RetentionPolicy.RUNTIME)
@interface RelationTypeInfo {
    RelationType value();
}

class RelationStdDeserializer extends StdDeserializer<Relation> implements ContextualDeserializer {

    private RelationType propertyRelationType;

    public RelationStdDeserializer() {
        this(null);
    }

    public RelationStdDeserializer(RelationType relationType) {
        super(Relation.class);
        this.propertyRelationType = relationType;
    }

    @Override
    public Relation deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
        JsonDeserializer<Object> deser = ctxt.findRootValueDeserializer(ctxt.getTypeFactory().constructType(Relation.class));
        Relation instance = (Relation) deser.deserialize(p, ctxt);
        if (this.propertyRelationType != null) {
            instance.setRelationtype(this.propertyRelationType);
        }
        return instance;
    }

    @Override
    public JsonDeserializer<?> createContextual(DeserializationContext ctxt, BeanProperty property) {
        RelationTypeInfo typeInfo = property.getMember().getAllAnnotations().get(RelationTypeInfo.class);

        return new RelationStdDeserializer(typeInfo.value());
    }
}

Above code for a payload:

{
  "owner": {
    "id": 1
  },
  "tenant": {
    "id": 2
  }
}

prints:

RelationsInput(owner=Relation(id=1, relationtype=OWNER), tenant=Relation(id=2, relationtype=TENANT))

See also:

score 0 · Answer 2 · answered Nov 24 '20 at 21:48

I am afraid there is not such thing. If you want to use something annotation like you could use custom de-serializers. Create first something like:

@RequiredArgsConstructor
public abstract class RelationTypeDeserializer extends JsonDeserializer<Relation> {
    private final RelationType relationType;

    @Override
    public Relation deserialize(JsonParser p, DeserializationContext ctxt)
            throws IOException, JsonProcessingException {
        Relation r = p.readValueAs(Relation.class);
        r.setRelationtype(relationType);
        return r;
    }
}

Then implement the actual ones:

public class OwnerDeserializer extends RelationTypeDeserializer {
    public OwnerDeserializer() {
        super(RelationType.OWNER);
    }   
}

and

public class TenantDeserializer extends RelationTypeDeserializer {
    public TenantDeserializer() {
        super(RelationType.TENANT);
    }
}

then use those like:

@Getter @Setter
public class RelationsInput {
    @JsonDeserialize(using = OwnerDeserializer.class)
    private Relation owner;
    @JsonDeserialize(using = TenantDeserializer.class)
    private Relation tenant;
}

score 0 · Answer 3 · answered Nov 25 '20 at 00:24

If you do what you ask for, you will always have the same value for the RelationType field. Anyway, one posible solution is using personalized serializer-deserializer like this:

public class RelationTypeJsonSerializer extends JsonSerializer<RelationType> {

    @Override
    public void serialize(RelationType value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
        String string = value.toString();//or something like that, convert the enum to string as you like
        gen.writeString(string);
    }
}

public class RelationTypeJsonDeserializer extends JsonDeserializer<RelationType> {

    @Override
    public RelationType deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
        String toString = p.getCodec().readValue(p, String.class);//read the value as string
        return RelationType.build(toString);//convert back the value to object, use switch if needed)
    }
}

ObjectMapper om = new ObjectMapper();
SimpleModule localDateModule = new SimpleModule("RelationType Module");
localDateModule.addSerializer(RelationType.class, new RelationTypeJsonSerializer());
localDateModule.addDeserializer(RelationType.class, new RelationTypeJsonDeserializer());
om.registerModule(localDateModule);

To convert the enum back and forward I recomend the use of map<String, RelationType>, super simple and work perfect, something like this:

Map<String, RelationType> map = new HashMap<String, RelationType>();
map.put("Some Type", RelationType.SOME_TYPE);
map.put("Some Other Type", RelationType.SOME_OTHER_TYPE);

And use the get(string) to serialize And get(value) to deserialize (find the key of some value) This is a general example when you want to serialize-deserialize something that don't have a default serializer-deserializer Look at this for more info How I parse Color java class to JSON with Jackson?

Jackson deserialization: Can I inject a value with an annotation on the field of the to deserializable object?

3 Answers3