How do I get a reference to the Jackson Object Mapper in a jersey2 / hk2 application

First there is no default ObjectMapper used by the Jackson provider. It doesn't use an ObjectMapper at all actually. It makes use of other Jackson APIs to handle the (de)serialization.

If you want to use/inject a single ObjectMapper instance, then you should just create a Factory for it

public class ObjectMapperFactory implements Factory<ObjectMapper> {    final ObjectMapper mapper = new ObjectMapper();    @Override    public ObjectMapper provide() {        return mapper;    }    @Override    public void dispose(ObjectMapper t) {}   }

Then bind it

register(new AbstractBinder(){    @Override    public void configure() {        bindFactory(ObjectMapperFactory.class)            .to(ObjectMapper.class).in(Singleton.class);    }});

One thing should be noted is that any configuration of the ObjectMapper is not thread safe. So say you tried to configure it from your resource method, those operations are not thread safe.

Another thing to note with the Jackson provider, is that if we provide a ContextResolver, like mentioned by @Laurentiu L, then the Jackson provider will switch to using our ObjectMapper. In which case, if you want to use that same ObjectMapper, then you can look it up in the Factory. For example

public class ObjectMapperFactory implements Factory<ObjectMapper> {    private final Providers providers;    final ObjectMapper mapper = new ObjectMapper();    public ObjectMapperFactory(@Context Providers providers) {        this.providers = providers;    }    @Override    public ObjectMapper provide() {        ContextResolver<ObjectMapper> resolver = providers.getContextResolver(                ObjectMapper.class, MediaType.APPLICATION_JSON);        if (resolver == null) { return mapper; }        return resolver.getContext(null);    }    @Override    public void dispose(ObjectMapper t) {}   }

For the above to work (use a single ObjectMapper), you need to make sure to implement the ContextResolver<ObjectMapper>, and make sure to annotation the ContextResolver with the corresponding @Produces and @Consumes media types.

Aside from the JacksonFeature you need to register a ContextResolver for ObjectMapper.

Simple example from the Documentation at 9.1.4.2. Configure and register

@Providerpublic class MyObjectMapperProvider implements ContextResolver<ObjectMapper> {    final ObjectMapper defaultObjectMapper;    public MyObjectMapperProvider() {        defaultObjectMapper = createDefaultMapper();    }    @Override    public ObjectMapper getContext(Class<?> type) {        return defaultObjectMapper;    }    private static ObjectMapper createDefaultMapper() {        final ObjectMapper result = new ObjectMapper();        result.configure(Feature.INDENT_OUTPUT, true);        return result;    }    // ...}

Complete code example available on Github

You will also need to register it

        .register(MyObjectMapperProvider.class)