private MultivaluedMap<String, Object> toMultivaluedMap(Map<String, Collection<String>> headers) {
    final MultivaluedHashMap<String, Object> mvHeaders = new MultivaluedHashMap<>();

    headers.forEach((key, value1) -> value1.forEach(value -> mvHeaders.add(key, value)));

    return mvHeaders;
  }
This module directs Feign's http requests to javax.ws.rs.client.Client . Ex:

<pre>
GitHub github =
    Feign.builder().client(new JaxRSClient()).target(GitHub.class, "https://api.github.com");
</pre>
jaxrs2/src/main/java/feign/jaxrs2/JAXRSClient.java