Serialize one class in two different ways with Jackson

Question

In one of our projects we use a java webapp talking to a MongoDB instance. In the database, we use DBRefs to keep track of some object relations. We (de)seriali

Answer 1

Use a custom JSONSerializer and apply your logic in the serialize method:

public static class FooReference {
    public DBRef<Foo> foo;

    @JsonSerialize(using = CustomSerializer.class)
    public Foo getFoo() {
        return foo.fetch();
    }
}

public class CustomSerializer extends JsonSerializer<Object> {
   public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider)
       throws IOException, JsonProcessingException {
     // jgen.writeObjectField ...
   }
}

Answer 2

From looking at options, it seems you can annotate properties to only be shown if a given View is passed to the ObjectMapper used for serialization. You could thus edit the class:

public static class FooReference {
    public DBRef<Foo> foo;

    @JsonView(Views.WebView.class)
    public Foo getFoo() {
        return foo.fetch();
    }
}

and provide:

class Views {
    static class WebView { }
}

and then serialize after creating a configuration with the correct view:

SerializationConfig conf = objectMapper.getSerializationConfig().withView(Views.WebView.class);
objectMapper.setSerializationConfig(conf);

Which would then serialize it. Not specifying the view when serializing with the MongoDB wrapper would mean the method would be ignored. Properties without a JsonView annotation are serialized by default, a behaviour you can change by specifying:

objectMapper.configure(SerializationConfig.Feature.DEFAULT_VIEW_INCLUSION, false);

More info is available on the Jackson Wiki.

There are still other alternatives, too, it turns out: there are Jackson MixIns which would let you override (de)serialization behaviour of parts of a class without modifying the class itself, and as of Jackson 2.0 (very recent release) there are filters, too.