Deserialization of interfaces using Jackson, where the interface implementation is specified in the serialized object

Question

I have the following sort of structure (simplified to hopefully make the problem clearer):

interface Settings {
    ...
}

interface Component {
    ...
}

class Container {
    Class<? extends Component> component;
    Settings settings;
}

@SettingsClass(MySettings.class)
class MyComponent implements Component{
    ...
}

class MySettings implements Settings{
    ...
}

If I serialize an instance of Container using Jackson, I get a JSON that looks a bit like:

{
    component: "my.package.MyComponent"
    settings: { ... }
}

This is exactly what I want.

But I can't deserialize that JSON because Jackson doesn't know which implementation of Settings to use. At run time, I can retrieve the SettingsClass annotation and identify which class the settings field should be deserialized to.

Is there a way for me to get Jackson to partially deserialize the JSON, and then have it deserialize the rest (ie the settings ) once I've been able to inspect the component and determine which Settings class to use?

Answer 1

Not really. I had to do something similar recently. I parsed into JsonNode and checked the property manually.

final JsonNode jsonRoot = new ObjectMapper().readTree(jsonString);
//...
Optional.ofNullable(jsonRoot.get("component")).map(JsonNode::textValue) ...

Then serialized the tree into the POJO.

new ObjectMapper().readerFor(theClass).readValue(jsonRoot)

Not amazing, but saves parsing the entire string twice at least.