How to control Jackson serialization of a library class

Question

I have a class (let us call it a Piece) containing a member of type com.jme3.math.ColorRGBA. With a default Jackson serialization the member is serialized not only as its members r, g, b and a, but then also using getters like getAlpha.

As this is obviously redundant, I would like to control the serialization and to serialize only those primary members. Are there some annotations that I can write to my class to control serialization of members with types not under my control, or some custom serializers for them?

I can probably write a custom serializer for the Piece class, though other than ColorRGBA serializer being too verbose, default serialization works fine for me for all other properties of Piece, therefore I would like to customize as little of it as possible.

I do not want to modify jme3 library source, the solution should be implemented outside of the ColorRGBA class.

Answer 1

You can use a mixin to make sure that the class is serialized as per your needs. Consider the following:

// The source class (where you do not own the source code)
public class ColorRGBA {
    public float a; // <-- Want to skip this one
    public float b;
    public float g;
    public float r;
}

Then, create the mixin where you ignore the a property.

// Create a mixin where you ignore the "a" property
@JsonIgnoreProperties("a")
public abstract class RGBMixin {
    // Other settings if required such as @JsonProperty on abstract methods.
}

Lastly, configure your mapper with the mixin:

ObjectMapper mapper = new ObjectMapper();
mapper.addMixInAnnotations(ColorRGBA.class, RGBMixin.class);
System.out.println(mapper.writeValueAsString(new ColorRGBA()));

The output will be:

{"b":0.0,"g":0.0,"r":0.0}

Note that the method ObjectMapper.addMixInAnnotations is deprecated from Jackson 2.5 and should be replaced with the more fluent version:

mapper.addMixIn(ColorRGBA.class, RGBMixin.class);

The JavaDocs can be found here

Answer 2

Option A

If you control the source of the class, can put this above class:

@JsonAutoDetect(fieldVisibility = Visibility.ANY, getterVisibility = Visibility.NONE, setterVisibility = Visibility.NONE)
public class ColorRGBA {

Option B

Otherwise you can set up an object mapper to ignore getters:

ObjectMapper mapper = new ObjectMapper();
mapper.setVisibilityChecker(mapper.getSerializationConfig().getDefaultVisibilityChecker()
                .withFieldVisibility(JsonAutoDetect.Visibility.ANY)
                .withGetterVisibility(JsonAutoDetect.Visibility.NONE)
                .withSetterVisibility(JsonAutoDetect.Visibility.NONE)
                .withCreatorVisibility(JsonAutoDetect.Visibility.NONE));

mapper.writeValue(stream, yourObject);

Option C

For more complicated requirements, you can write your own VisibilityChecker implementation.