[BUG] (JAVA 11 Native HTTP client) No mapper for XML instantiated, thus fails with `JsonParseException: Unexpected character ('<' (code 60))`

Generated a client for an API that sends XML output exclusively using the java generator with <library>native</library> (ping @bbdouglas).

It correctly adds header("Accept", "application/xml") to the HttpRequest, but however fails on executing any of the endpoint methods with

org.openapitools.client.ApiException: com.fasterxml.jackson.core.JsonParseException: Unexpected character ('<' (code 60)): expected a valid value (JSON String, Number, Array, Object or token 'null', 'true' or 'false') at [Source: (jdk.internal.net.http.ResponseSubscribers$HttpResponseInputStream); line: 1, column: 2]
java.lang.RuntimeException: org.openapitools.client.ApiException: com.fasterxml.jackson.core.JsonParseException: Unexpected character ('<' (code 60)): expected a valid value (JSON String, Number, Array, Object or token 'null', 'true' or 'false')

as the mapper being used is the default JSON mapper, while it should use a new com.fasterxml.jackson.dataformat.xml.XmlMapper instead in this case.

openapi-generator version

7.4

Suggest a fix

The obvious (and working) fix is to use an XmlMapper instead of ObjectMapper for Deserialization (the readValue() api is identical) whenever application/xml is requested.

Start with the generated Java 11 native HTTP client deserialization path and inspect how an application/xml response is mapped. Compare the current default JSON mapper behavior with the proposed XmlMapper approach; done means an XML-only API response can be deserialized without the reported JsonParseException.