trying to get ISO8601 dates in dropwizard JSON

gistfile1.txt

    @Override
    public void run(ApiServiceConfiguration config, Environment env) throws Exception {
        ...
        // works
        env.getObjectMapperFactory().setDateFormat(new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSZ"));
        // works
        env.getObjectMapperFactory().setDateFormat(new ISO8601DateFormat.getInstance());
        // doesn't work
        env.getObjectMapperFactory().setDateFormat(ISO8601DateFormat.getInstance());
        ...
    }