ProblemDetail XML support via Jackson

Closes gh-29927

spring-web/src/main/java/org/springframework/http/codec/json/Jackson2CodecSupport.java

@@ -80,9 +80,6 @@ public abstract class Jackson2CodecSupport {
 			new MediaType("application", "*+json"),
 			MediaType.APPLICATION_NDJSON);
 
-	private static final List<MimeType> problemDetailMimeTypes =
-			Collections.singletonList(MediaType.APPLICATION_PROBLEM_JSON);
-
 
 	protected final Log logger = HttpLogging.forLogName(getClass());
 
@@ -186,7 +183,16 @@ public abstract class Jackson2CodecSupport {
 		if (!CollectionUtils.isEmpty(result)) {
 			return result;
 		}
-		return (ProblemDetail.class.isAssignableFrom(elementClass) ? problemDetailMimeTypes : getMimeTypes());
+		return (ProblemDetail.class.isAssignableFrom(elementClass) ? getMediaTypesForProblemDetail() : getMimeTypes());
+	}
+
+	/**
+	 * Return the supported media type(s) for {@link ProblemDetail}.
+	 * By default, an empty list, unless overridden in subclasses.
+	 * @since 6.0.5
+	 */
+	protected List<MimeType> getMediaTypesForProblemDetail() {
+		return Collections.emptyList();
 	}
 
 	protected boolean supportsMimeType(@Nullable MimeType mimeType) {

spring-web/src/main/java/org/springframework/http/codec/json/Jackson2JsonEncoder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@
 package org.springframework.http.codec.json;
 
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 
@@ -46,6 +47,10 @@ import org.springframework.util.MimeType;
  */
 public class Jackson2JsonEncoder extends AbstractJackson2Encoder {
 
+	private static final List<MimeType> problemDetailMimeTypes =
+			Collections.singletonList(MediaType.APPLICATION_PROBLEM_JSON);
+
+
 	@Nullable
 	private final PrettyPrinter ssePrettyPrinter;
 
@@ -68,6 +73,11 @@ public class Jackson2JsonEncoder extends AbstractJackson2Encoder {
 	}
 
 
+	@Override
+	protected List<MimeType> getMediaTypesForProblemDetail() {
+		return problemDetailMimeTypes;
+	}
+
 	@Override
 	protected ObjectWriter customizeWriter(ObjectWriter writer, @Nullable MimeType mimeType,
 			ResolvableType elementType, @Nullable Map<String, Object> hints) {

spring-web/src/main/java/org/springframework/http/converter/json/AbstractJackson2HttpMessageConverter.java

@@ -91,9 +91,6 @@ public abstract class AbstractJackson2HttpMessageConverter extends AbstractGener
 		ENCODINGS.put("US-ASCII", JsonEncoding.UTF8);
 	}
 
-	private static final List<MediaType> problemDetailMediaTypes =
-			Collections.singletonList(MediaType.APPLICATION_PROBLEM_JSON);
-
 
 	protected ObjectMapper defaultObjectMapper;
 
@@ -209,13 +206,23 @@ public abstract class AbstractJackson2HttpMessageConverter extends AbstractGener
 		if (!CollectionUtils.isEmpty(result)) {
 			return result;
 		}
-		return (ProblemDetail.class.isAssignableFrom(clazz) ? problemDetailMediaTypes : getSupportedMediaTypes());
+		return (ProblemDetail.class.isAssignableFrom(clazz) ?
+				getMediaTypesForProblemDetail() : getSupportedMediaTypes());
 	}
 
 	private Map<Class<?>, Map<MediaType, ObjectMapper>> getObjectMapperRegistrations() {
 		return (this.objectMapperRegistrations != null ? this.objectMapperRegistrations : Collections.emptyMap());
 	}
 
+	/**
+	 * Return the supported media type(s) for {@link ProblemDetail}.
+	 * By default, an empty list, unless overridden in subclasses.
+	 * @since 6.0.5
+	 */
+	protected List<MediaType> getMediaTypesForProblemDetail() {
+		return Collections.emptyList();
+	}
+
 	/**
 	 * Whether to use the {@link DefaultPrettyPrinter} when writing JSON.
 	 * This is a shortcut for setting up an {@code ObjectMapper} as follows:

spring-web/src/main/java/org/springframework/http/converter/json/Jackson2ObjectMapperBuilder.java

@@ -99,6 +99,10 @@ import org.springframework.util.xml.StaxUtils;
  */
 public class Jackson2ObjectMapperBuilder {
 
+	private static boolean jackson2XmlPresent = ClassUtils.isPresent(
+			"com.fasterxml.jackson.dataformat.xml.XmlMapper", Jackson2ObjectMapperBuilder.class.getClassLoader());
+
+
 	private final Map<Class<?>, Class<?>> mixIns = new LinkedHashMap<>();
 
 	private final Map<Class<?>, JsonSerializer<?>> serializers = new LinkedHashMap<>();
@@ -755,7 +759,12 @@ public class Jackson2ObjectMapperBuilder {
 			objectMapper.setFilterProvider(this.filters);
 		}
 
-		objectMapper.addMixIn(ProblemDetail.class, ProblemDetailJacksonMixin.class);
+		if (jackson2XmlPresent) {
+			objectMapper.addMixIn(ProblemDetail.class, ProblemDetailJacksonXmlMixin.class);
+		}
+		else {
+			objectMapper.addMixIn(ProblemDetail.class, ProblemDetailJacksonMixin.class);
+		}
 		this.mixIns.forEach(objectMapper::addMixIn);
 
 		if (!this.serializers.isEmpty() || !this.deserializers.isEmpty()) {

spring-web/src/main/java/org/springframework/http/converter/json/MappingJackson2HttpMessageConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,8 @@
 package org.springframework.http.converter.json;
 
 import java.io.IOException;
+import java.util.Collections;
+import java.util.List;
 
 import com.fasterxml.jackson.core.JsonGenerator;
 import com.fasterxml.jackson.databind.ObjectMapper;
@@ -45,6 +47,10 @@ import org.springframework.lang.Nullable;
  */
 public class MappingJackson2HttpMessageConverter extends AbstractJackson2HttpMessageConverter {
 
+	private static final List<MediaType> problemDetailMediaTypes =
+			Collections.singletonList(MediaType.APPLICATION_PROBLEM_JSON);
+
+
 	@Nullable
 	private String jsonPrefix;
 
@@ -88,6 +94,11 @@ public class MappingJackson2HttpMessageConverter extends AbstractJackson2HttpMes
 	}
 
 
+	@Override
+	protected List<MediaType> getMediaTypesForProblemDetail() {
+		return problemDetailMediaTypes;
+	}
+
 	@Override
 	protected void writePrefix(JsonGenerator generator, Object object) throws IOException {
 		if (this.jsonPrefix != null) {

spring-web/src/main/java/org/springframework/http/converter/json/ProblemDetailJacksonXmlMixin.java

@@ -0,0 +1,72 @@
+/*
+ * Copyright 2002-2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.http.converter.json;
+
+import java.net.URI;
+import java.util.Map;
+
+import com.fasterxml.jackson.annotation.JsonAnyGetter;
+import com.fasterxml.jackson.annotation.JsonAnySetter;
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty;
+import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlRootElement;
+
+import org.springframework.lang.Nullable;
+
+import static com.fasterxml.jackson.annotation.JsonInclude.Include.NON_EMPTY;
+
+/**
+ * Intended to be identical to {@link ProblemDetailJacksonMixin} but for used
+ * instead of it when jackson-dataformat-xml is on the classpath. Customizes the
+ * XML root element name and adds namespace information.
+ *
+ * <p>Note: Unfortunately, we cannot just use {@code JsonRootName} to specify
+ * the namespace since that is not inherited by fields of the class. This is
+ * why we need a dedicated mixin for use when jackson-dataformat-xml is on the
+ * classpath. For more details, see
+ * <a href="https://github.com/FasterXML/jackson-dataformat-xml/issues/355">FasterXML/jackson-dataformat-xml#355</a>.
+ *
+ * @author Rossen Stoyanchev
+ * @since 6.0.5
+ */
+@JsonInclude(NON_EMPTY)
+@JacksonXmlRootElement(localName = "problem", namespace = "urn:ietf:rfc:7807")
+public interface ProblemDetailJacksonXmlMixin {
+
+	@JacksonXmlProperty(namespace = "urn:ietf:rfc:7807")
+	URI getType();
+
+	@JacksonXmlProperty(namespace = "urn:ietf:rfc:7807")
+	String getTitle();
+
+	@JacksonXmlProperty(namespace = "urn:ietf:rfc:7807")
+	int getStatus();
+
+	@JacksonXmlProperty(namespace = "urn:ietf:rfc:7807")
+	String getDetail();
+
+	@JacksonXmlProperty(namespace = "urn:ietf:rfc:7807")
+	URI getInstance();
+
+	@JsonAnySetter
+	void setProperty(String name, @Nullable Object value);
+
+	@JsonAnyGetter
+	@JacksonXmlProperty(namespace = "urn:ietf:rfc:7807")
+	Map<String, Object> getProperties();
+
+}

spring-web/src/main/java/org/springframework/http/converter/xml/MappingJackson2XmlHttpMessageConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,8 @@
 package org.springframework.http.converter.xml;
 
 import java.nio.charset.StandardCharsets;
+import java.util.Collections;
+import java.util.List;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.dataformat.xml.XmlMapper;
@@ -42,6 +44,10 @@ import org.springframework.util.Assert;
  */
 public class MappingJackson2XmlHttpMessageConverter extends AbstractJackson2HttpMessageConverter {
 
+	private static final List<MediaType> problemDetailMediaTypes =
+			Collections.singletonList(MediaType.APPLICATION_PROBLEM_XML);
+
+
 	/**
 	 * Construct a new {@code MappingJackson2XmlHttpMessageConverter} using default configuration
 	 * provided by {@code Jackson2ObjectMapperBuilder}.
@@ -74,4 +80,9 @@ public class MappingJackson2XmlHttpMessageConverter extends AbstractJackson2Http
 		super.setObjectMapper(objectMapper);
 	}
 
+	@Override
+	protected List<MediaType> getMediaTypesForProblemDetail() {
+		return problemDetailMediaTypes;
+	}
+
 }