Private static field in Java interface

You cann't have a private static field in Java interface even though you use Java8 which you can have default implementation.

There is a hack for this.

public interface InterfaceContainsPrivateStaticFields {
    class _PrivateStaticFields {
        private static ObjectMapper mapper = new ObjectMapper(); // only accessible in this interface.
    }

    default ObjectReader test() {
        return _PrivateStaticFields.mapper.reader();
    }
}

github.com

You can see techniques that enable jackson processing faster in this PR.