Jackson deserialize based on type

Question

Lets say I have JSON of the following format:

{
    \"type\" : \"Foo\"
    \"data\" : {
        \"object\" : {
            \"id\" : \"1\"
            \"fizz\         


        

Answer 1

Custom deserializer approach

You could use a custom deserializer that checks the type property to parse the object property into the most suitable class.

First define an interface that will be implemented by Foo and Bar classes:

public interface Model {

}

public class Foo implements Model {

    // Fields, getters and setters
}

public class Bar implements Model {

    // Fields, getters and setters
}

Then define your Wrapper and Data classes:

public class Wrapper {

    private String type;

    private Data data;

    // Getters and setters
}

public class Data {

    @JsonDeserialize(using = ModelDeserializer.class)
    private Model object;

    private Metadata metadata;

    private Owner owner;

    // Getters and setters
}

The object field is annotated with @JsonDeserialize, indicating the deserializer that will be used for the object property.

The deserializer is defined as following:

public class ModelDeserializer extends JsonDeserializer {

    @Override
    public Model deserialize(JsonParser jp, DeserializationContext ctxt)
        throws IOException, JsonMappingException {

        // Get reference to ObjectCodec
        ObjectCodec codec = jp.getCodec();

        // Parse "object" node into Jackson's tree model
        JsonNode node = codec.readTree(jp);

        // Get value of the "type" property
        String type = ((Wrapper) jp.getParsingContext().getParent()
            .getCurrentValue()).getType();

        // Check the "type" property and map "object" to the suitable class
        switch (type) {

            case "Foo":
                return codec.treeToValue(node, Foo.class);

            case "Bar":
                return codec.treeToValue(node, Bar.class);

            default:
                throw new JsonMappingException(jp, 
                    "Invalid value for the \"type\" property");
        }
    }
}

The JSON document can be deserialized as following:

ObjectMapper mapper = new ObjectMapper();
Wrapper wrapper = mapper.readValue(json, Wrapper.class);  

Alternatively to this custom deserializer, consider an annotations-only approach.