Java: Jackson polymorphic JSON deserialization of an object with an interface property?

Question

I am using Jackson's ObjectMapper to deserialize a JSON representation of an object that contains an interface as one of its properties. A simplified version of the code can be seen here:

https://gist.github.com/sscovil/8735923

Basically, I have a class Asset with two properties: type and properties. The JSON model looks like this:

{
    "type": "document",
    "properties": {
        "source": "foo",
        "proxy": "bar"
    }
}

The properties property is defined as an interface called AssetProperties, and I have several classes that implement it (e.g. DocumentAssetProperties, ImageAssetProperties). The idea is that image files have different properties (height, width) than document files, etc.

I've worked off of the examples in this article, read through docs and questions here on SO and beyond, and experimented with different configurations in the @JsonTypeInfo annotation parameters, but haven't been able to crack this nut. Any help would be greatly appreciated.

Most recently, the exception I'm getting is this:

java.lang.AssertionError: Could not deserialize JSON.
...
Caused by: org.codehaus.jackson.map.JsonMappingException: Could not resolve type id 'source' into a subtype of [simple type, class AssetProperties]

Thanks in advance!

SOLUTION:

With many thanks to @Micha? Ziober, I was able to resolve this issue. I was also able to use an Enum as a type id, which took a bit of Googling. Here is an updated Gist with working code:

https://gist.github.com/sscovil/8788339

Answer 1

You should use JsonTypeInfo.As.EXTERNAL_PROPERTY instead of JsonTypeInfo.As.PROPERTY. In this scenario your Asset class should look like this:

class Asset {

    @JsonTypeInfo(
            use = JsonTypeInfo.Id.NAME,
            include = JsonTypeInfo.As.EXTERNAL_PROPERTY,
            property = "type")
    @JsonSubTypes({
        @JsonSubTypes.Type(value = ImageAssetProperties.class, name = "image"),
        @JsonSubTypes.Type(value = DocumentAssetProperties.class, name = "document") })
    private AssetProperties properties;

    public AssetProperties getProperties() {
        return properties;
    }

    public void setProperties(AssetProperties properties) {
        this.properties = properties;
    }

    @Override
    public String toString() {
        return "Asset [properties("+properties.getClass().getSimpleName()+")=" + properties + "]";
    }
}

See also my answer in this question: Jackson JsonTypeInfo.As.EXTERNAL_PROPERTY doesn't work as expected.