How do I add a Jackson mixin to a reader and not to the objectmapper?

Question

I have an object that I would like to serialize with an attribute in one part of my program, but without in a different part. I also have an ObjectMapper which is extensively customized that I use for both serializations. My first inclination was to use a Mixin to tweak if the attribute is shown, but it seems that you can only put those on the ObjectMapper and not on a reader returned by the ObjectMapper. Basically the code I would like to be able to write would look like the following.

ObjectMapper myMapper = new ObjectMapper(); // in reality there is a lot of customization
Foo foo = myMapper.reader().withMixin(Foo.class, FooMixin.class).readValue(jsonParser, Foo.class);

Answer 1

Correct. You can not change mix-ins on-the-fly, however: since they are used for introspection of (de)serializers, and results (actual (de)serializers) are cached, they must be added as part of the initial configuration. This is why neither ObjectReader nor ObjectWriter exposes methods to change mix-ins: they only allow changing of things that can be dynamically changed, on per-call basis.

But perhaps mix-ins are not the best way to do this: have you considered using JSON Views instead? Active view in use can be changed separately for each (de)serialization.