@JacksonXmlRootElement is ignored with Jackson 3

[sdeleuze]

With Jackson 3.0.0-rc4:

@JsonInclude(NON_EMPTY)
@JacksonXmlRootElement(localName = "problem", namespace = ProblemDetailJacksonXmlMixin.NAMESPACE)
public interface ProblemDetailJacksonXmlMixin {

	/** RFC 7807 (obsoleted by RFC 9457) namespace. */
	String NAMESPACE = "urn:ietf:rfc:7807";


	@JacksonXmlProperty(namespace = NAMESPACE)
	URI getType();

	@JacksonXmlProperty(namespace = NAMESPACE)
	String getTitle();

	@JacksonXmlProperty(namespace = NAMESPACE)
	int getStatus();

	@JacksonXmlProperty(namespace = NAMESPACE)
	String getDetail();

	@JacksonXmlProperty(namespace = NAMESPACE)
	URI getInstance();

	@JsonAnySetter
	void setProperty(String name, @Nullable Object value);

	@JsonAnyGetter
	@JacksonXmlProperty(namespace = NAMESPACE)
	Map<String, Object> getProperties();

}

@SuppressWarnings("serial")
private static class MyProblemDetail extends ProblemDetail {

	private static final long serialVersionUID = 848059476504348430L;

	public MyProblemDetail(HttpStatus status) {
		super(status.value());
	}
}

@Test
void test() {
	XmlMapper mapper = XmlMapper.builder()
			.addMixIn(ProblemDetail.class, ProblemDetailJacksonXmlMixin.class)
			.build();
	MyProblemDetail problemDetail = new MyProblemDetail(HttpStatus.BAD_REQUEST);
	System.out.println(mapper.writerFor(MyProblemDetail.class).writeValueAsString(problemDetail));
}

Jackson 2.x prints as expected:

<problem xmlns="urn:ietf:rfc:7807"><type>about:blank</type><title>Bad Request</title><status>400</status></problem>

Jackson 3.x ignores the @JacksonXmlRootElement annotation and prints:

<MyProblemDetail><status>400</status><title>Bad Request</title><type>about:blank</type></MyProblemDetail>

This is breaking Spring support for RFC 9457.

[pjfanning]

try builder().enable(SerializationFeature.WRAP_ROOT_VALUE)

[sdeleuze]

Thanks for the proposal, but I don't think I can configure that, since it will break other use cases (I am dealing here with JacksonXmlHttpMessageConverter default XmlMapper).

Also no change of behavior seems documented for that between 2.x and 3.x in the Javadoc, and @JsonRootName works by default (but is not usable for us due to #355), so I tend to think this is a genuine bug/regression.

[cowtowncoder]

Sounds like potential bug. I assume 2.x refers to 2.19.0?

I think there were some fixes wrt property name merging -- and perhaps namespace-only case was broken. Will need to look into this.

[sdeleuze]

I tested with 2.18.3 but that always worked on 2.x as far as I can tell. Seems also broken without mixins involved.

[cowtowncoder]

Right, but what I am trying to figure out is whether it broke with 2.19 or 3.0. Has not been reported for 2.19 fwtw. And none of XML changes in https://github.com/FasterXML/jackson/wiki/Jackson-Release-2.19 sound suspicious.

I can check this later on when I have time, just thought to confirm version you used.

[sdeleuze]

Just tested, can't reproduce with Jackson 2.19.0, that's a Jackson 3 regression.

[cowtowncoder]

Thanks!

[cowtowncoder]

@sdeleuze Looks like reproduction is incomplete: it is missing ProblemDetail. Could you add that?

Also ideally I think we'd have minimal reproduction (just remove all but one of fields for POJO).
But I can do that.

[sdeleuze]

Hum, I think I understand what happens now. @JacksonXmlRootElement is not part of jackson-annotations but jackson-dataformat-xml dependency so it has changed of package as part of the Jackson 3 migration, hence the fact com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlRootElement is not recognized with Jackson 3.

[cowtowncoder]

Ah. Yeah, in-module annotations (jackson-databind has some too) are bit challenging as unlike jackson-annotations, their Java packages change.