Add ProblemDetail and `@ExceptionHandler` support

ProblemDetail is a representation of an RFC 7807 "problem", and this
commits adds support for it in Spring MVC and WebFlux as a return value
from `@ExceptionHandler` methods, optionally wrapped with
ResponseEntity for headers.

See gh-27052

spring-web/src/main/java/org/springframework/http/ProblemDetail.java

@@ -0,0 +1,279 @@
+/*
+ * Copyright 2002-2022 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;
+
+import java.net.URI;
+
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
+/**
+ * Representation of an RFC 7807 problem detail, including all RFC-defined
+ * fields. For an extended response with more fields, create a subclass that
+ * exposes the additional fields.
+ *
+ * @author Rossen Stoyanchev
+ * @since 6.0
+ *
+ * @see <a href="https://datatracker.ietf.org/doc/html/rfc7807">RFC 7807</a>
+ * @see org.springframework.web.ErrorResponse
+ * @see org.springframework.web.ErrorResponseException
+ */
+public class ProblemDetail {
+
+	private static final URI BLANK_TYPE = URI.create("about:blank");
+
+
+	private URI type = BLANK_TYPE;
+
+	@Nullable
+	private String title;
+
+	private int status;
+
+	@Nullable
+	private String detail;
+
+	@Nullable
+	private URI instance;
+
+
+	/**
+	 * Protected constructor for subclasses.
+	 * <p>To create a {@link ProblemDetail} instance, use static factory methods,
+	 * {@link #forStatus(HttpStatus)} or {@link #forRawStatusCode(int)}.
+	 * @param rawStatusCode the response status to use
+	 */
+	protected ProblemDetail(int rawStatusCode) {
+		this.status = rawStatusCode;
+	}
+
+	/**
+	 * Copy constructor that could be used from a subclass to re-create a
+	 * {@code ProblemDetail} in order to extend it with more fields.
+	 */
+	protected ProblemDetail(ProblemDetail other) {
+		this.type = other.type;
+		this.title = other.title;
+		this.status = other.status;
+		this.detail = other.detail;
+		this.instance = other.instance;
+	}
+
+
+	/**
+	 * Variant of {@link #setType(URI)} for chained initialization.
+	 * @param type the problem type
+	 * @return the same instance
+	 */
+	public ProblemDetail withType(URI type) {
+		setType(type);
+		return this;
+	}
+
+	/**
+	 * Variant of {@link #setTitle(String)} for chained initialization.
+	 * @param title the problem title
+	 * @return the same instance
+	 */
+	public ProblemDetail withTitle(@Nullable String title) {
+		setTitle(title);
+		return this;
+	}
+
+	/**
+	 * Variant of {@link #setStatus(int)} for chained initialization.
+	 * @param status the response status for the problem
+	 * @return the same instance
+	 */
+	public ProblemDetail withStatus(HttpStatus status) {
+		Assert.notNull(status, "HttpStatus is required");
+		setStatus(status.value());
+		return this;
+	}
+
+	/**
+	 * Variant of {@link #setStatus(int)} for chained initialization.
+	 * @param status the response status value for the problem
+	 * @return the same instance
+	 */
+	public ProblemDetail withRawStatusCode(int status) {
+		setStatus(status);
+		return this;
+	}
+
+	/**
+	 * Variant of {@link #setDetail(String)} for chained initialization.
+	 * @param detail the problem detail
+	 * @return the same instance
+	 */
+	public ProblemDetail withDetail(@Nullable String detail) {
+		setDetail(detail);
+		return this;
+	}
+
+	/**
+	 * Variant of {@link #setInstance(URI)} for chained initialization.
+	 * @param instance the problem instance URI
+	 * @return the same instance
+	 */
+	public ProblemDetail withInstance(@Nullable URI instance) {
+		setInstance(instance);
+		return this;
+	}
+
+
+	// Setters for deserialization
+
+	/**
+	 * Setter for the {@link #getType() problem type}.
+	 * <p>By default, this is {@link #BLANK_TYPE}.
+	 * @param type the problem type
+	 * @see #withType(URI)
+	 */
+	public void setType(URI type) {
+		Assert.notNull(type, "'type' is required");
+		this.type = type;
+	}
+
+	/**
+	 * Setter for the {@link #getTitle() problem title}.
+	 * <p>By default, if not explicitly set and the status is well-known, this
+	 * is sourced from the {@link HttpStatus#getReasonPhrase()}.
+	 * @param title the problem title
+	 * @see #withTitle(String)
+	 */
+	public void setTitle(@Nullable String title) {
+		this.title = title;
+	}
+
+	/**
+	 * Setter for the {@link #getStatus() problem status}.
+	 * @param status the problem status
+	 * @see #withStatus(HttpStatus)
+	 * @see #withRawStatusCode(int)
+	 */
+	public void setStatus(int status) {
+		this.status = status;
+	}
+
+	/**
+	 * Setter for the {@link #getDetail() problem detail}.
+	 * <p>By default, this is not set.
+	 * @param detail the problem detail
+	 * @see #withDetail(String)
+	 */
+	public void setDetail(@Nullable String detail) {
+		this.detail = detail;
+	}
+
+	/**
+	 * Setter for the {@link #getInstance() problem instance}.
+	 * <p>By default, when {@code ProblemDetail} is returned from an
+	 * {@code @ExceptionHandler} method, this is initialized to the request path.
+	 * @param instance the problem instance
+	 * @see #withInstance(URI)
+	 */
+	public void setInstance(@Nullable URI instance) {
+		this.instance = instance;
+	}
+
+
+	// Getters
+
+	/**
+	 * Return the configured {@link #setType(URI) problem type}.
+	 */
+	public URI getType() {
+		return this.type;
+	}
+
+	/**
+	 * Return the configured {@link #setTitle(String) problem title}.
+	 */
+	@Nullable
+	public String getTitle() {
+		if (this.title == null) {
+			HttpStatus httpStatus = HttpStatus.resolve(this.status);
+			if (httpStatus != null) {
+				return httpStatus.getReasonPhrase();
+			}
+		}
+		return this.title;
+	}
+
+	/**
+	 * Return the status associated with the problem, provided either to the
+	 * constructor or configured via {@link #setStatus(int)}.
+	 */
+	public int getStatus() {
+		return this.status;
+	}
+
+	/**
+	 * Return the configured {@link #setDetail(String) problem detail}.
+	 */
+	@Nullable
+	public String getDetail() {
+		return this.detail;
+	}
+
+	/**
+	 * Return the configured {@link #setInstance(URI) problem instance}.
+	 */
+	@Nullable
+	public URI getInstance() {
+		return this.instance;
+	}
+
+
+	@Override
+	public String toString() {
+		return getClass().getSimpleName() + "[" + initToStringContent() + "]";
+	}
+
+	/**
+	 * Return a String representation of the {@code ProblemDetail} fields.
+	 * Subclasses can override this to append additional fields.
+	 */
+	protected String initToStringContent() {
+		return "type='" + this.type + "'" +
+				", title='" + getTitle() + "'" +
+				", status=" + getStatus() +
+				", detail='" + getDetail() + "'" +
+				", instance='" + getInstance() + "'";
+	}
+
+
+	// Static factory methods
+
+	/**
+	 * Create a {@code ProblemDetail} instance with the given status code.
+	 */
+	public static ProblemDetail forStatus(HttpStatus status) {
+		Assert.notNull(status, "HttpStatus is required");
+		return forRawStatusCode(status.value());
+	}
+
+	/**
+	 * Create a {@code ProblemDetail} instance with the given status value.
+	 */
+	public static ProblemDetail forRawStatusCode(int status) {
+		return new ProblemDetail(status);
+	}
+
+}

spring-web/src/main/java/org/springframework/http/ResponseEntity.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -260,6 +260,27 @@ public class ResponseEntity<T> extends HttpEntity<T> {
 		return body.map(ResponseEntity::ok).orElseGet(() -> notFound().build());
 	}
 
+	/**
+	 * Create a builder for a {@code ResponseEntity} with the given
+	 * {@link ProblemDetail} as the body, also matching to its
+	 * {@link ProblemDetail#getStatus() status}. An {@code @ExceptionHandler}
+	 * method can use to add response headers, or otherwise it can return
+	 * {@code ProblemDetail}.
+	 * @param body the details for an HTTP error response
+	 * @return the created builder
+	 * @since 6.0
+	 */
+	public static HeadersBuilder<?> of(ProblemDetail body) {
+		return new DefaultBuilder(body.getStatus()) {
+
+			@SuppressWarnings("unchecked")
+			@Override
+			public <T> ResponseEntity<T> build() {
+				return (ResponseEntity<T>) body(body);
+			}
+		};
+	}
+
 	/**
 	 * Create a new builder with a {@linkplain HttpStatus#CREATED CREATED} status
 	 * and a location header set to the given URI.

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/ResponseEntityResultHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -16,6 +16,7 @@
 
 package org.springframework.web.reactive.result.method.annotation;
 
+import java.net.URI;
 import java.time.Instant;
 import java.util.List;
 import java.util.Set;
@@ -30,6 +31,7 @@ import org.springframework.http.HttpEntity;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
+import org.springframework.http.ProblemDetail;
 import org.springframework.http.RequestEntity;
 import org.springframework.http.ResponseEntity;
 import org.springframework.http.codec.HttpMessageWriter;
@@ -41,7 +43,8 @@ import org.springframework.web.reactive.accept.RequestedContentTypeResolver;
 import org.springframework.web.server.ServerWebExchange;
 
 /**
- * Handles {@link HttpEntity} and {@link ResponseEntity} return values.
+ * Handles return values of type {@link HttpEntity}, {@link ResponseEntity},
+ * {@link HttpHeaders}, and {@link ProblemDetail}.
  *
  * <p>By default the order for this result handler is set to 0. It is generally
  * safe to place it early in the order as it looks for a concrete return type.
@@ -100,10 +103,12 @@ public class ResponseEntityResultHandler extends AbstractMessageWriterResultHand
 		return valueType;
 	}
 
-	private boolean isSupportedType(@Nullable Class<?> clazz) {
-		return (clazz != null && ((HttpEntity.class.isAssignableFrom(clazz) &&
-				!RequestEntity.class.isAssignableFrom(clazz)) ||
-				HttpHeaders.class.isAssignableFrom(clazz)));
+	private boolean isSupportedType(@Nullable Class<?> type) {
+		if (type == null) {
+			return false;
+		}
+		return ((HttpEntity.class.isAssignableFrom(type) && !RequestEntity.class.isAssignableFrom(type)) ||
+				HttpHeaders.class.isAssignableFrom(type) || ProblemDetail.class.isAssignableFrom(type));
 	}
 
 
@@ -136,11 +141,21 @@ public class ResponseEntityResultHandler extends AbstractMessageWriterResultHand
 			else if (returnValue instanceof HttpHeaders) {
 				httpEntity = new ResponseEntity<>((HttpHeaders) returnValue, HttpStatus.OK);
 			}
+			else if (returnValue instanceof ProblemDetail detail) {
+				httpEntity = new ResponseEntity<>(returnValue, HttpHeaders.EMPTY, detail.getStatus());
+			}
 			else {
 				throw new IllegalArgumentException(
 						"HttpEntity or HttpHeaders expected but got: " + returnValue.getClass());
 			}
 
+			if (httpEntity.getBody() instanceof ProblemDetail detail) {
+				if (detail.getInstance() == null) {
+					URI path = URI.create(exchange.getRequest().getPath().value());
+					detail.setInstance(path);
+				}
+			}
+
 			if (httpEntity instanceof ResponseEntity) {
 				exchange.getResponse().setRawStatusCode(
 						((ResponseEntity<?>) httpEntity).getStatusCodeValue());

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/ResponseEntityResultHandlerTests.java

@@ -46,6 +46,7 @@ import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
+import org.springframework.http.ProblemDetail;
 import org.springframework.http.ResponseEntity;
 import org.springframework.http.codec.EncoderHttpMessageWriter;
 import org.springframework.http.codec.HttpMessageWriter;
@@ -129,6 +130,9 @@ public class ResponseEntityResultHandlerTests {
 		returnType = on(TestController.class).resolveReturnType(HttpHeaders.class);
 		assertThat(this.resultHandler.supports(handlerResult(value, returnType))).isTrue();
 
+		returnType = on(TestController.class).resolveReturnType(ProblemDetail.class);
+		assertThat(this.resultHandler.supports(handlerResult(value, returnType))).isTrue();
+
 		// SPR-15785
 		value = ResponseEntity.ok("testing");
 		returnType = on(TestController.class).resolveReturnType(Object.class);
@@ -232,6 +236,26 @@ public class ResponseEntityResultHandlerTests {
 		testHandle(returnValue, returnType);
 	}
 
+	@Test
+	public void handleProblemDetail() {
+		ProblemDetail problemDetail = ProblemDetail.forStatus(HttpStatus.BAD_REQUEST);
+		MethodParameter returnType = on(TestController.class).resolveReturnType(ProblemDetail.class);
+		HandlerResult result = handlerResult(problemDetail, returnType);
+		MockServerWebExchange exchange = MockServerWebExchange.from(get("/path"));
+		exchange.getResponse().getHeaders().setContentType(MediaType.APPLICATION_PROBLEM_JSON);
+		this.resultHandler.handleResult(exchange, result).block(Duration.ofSeconds(5));
+
+		assertThat(exchange.getResponse().getStatusCode()).isEqualTo(HttpStatus.BAD_REQUEST);
+		assertThat(exchange.getResponse().getHeaders().size()).isEqualTo(2);
+		assertThat(exchange.getResponse().getHeaders().getContentType()).isEqualTo(MediaType.APPLICATION_PROBLEM_JSON);
+		assertResponseBody(exchange,
+				"{\"type\":\"about:blank\"," +
+						"\"title\":\"Bad Request\"," +
+						"\"status\":400," +
+						"\"detail\":null," +
+						"\"instance\":\"/path\"}");
+	}
+
 	@Test
 	public void handleReturnValueLastModified() throws Exception {
 		Instant currentTime = Instant.now().truncatedTo(ChronoUnit.SECONDS);
@@ -505,6 +529,8 @@ public class ResponseEntityResultHandlerTests {
 
 		ResponseEntity<Person> responseEntityPerson() { return null; }
 
+		ProblemDetail problemDetail() { return null; }
+
 		HttpHeaders httpHeaders() { return null; }
 
 		Mono<ResponseEntity<String>> mono() { return null; }

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/HttpEntityMethodProcessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -19,6 +19,7 @@ package org.springframework.web.servlet.mvc.method.annotation;
 import java.io.IOException;
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
+import java.net.URI;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -32,6 +33,7 @@ import org.springframework.core.ResolvableType;
 import org.springframework.http.HttpEntity;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
+import org.springframework.http.ProblemDetail;
 import org.springframework.http.RequestEntity;
 import org.springframework.http.ResponseEntity;
 import org.springframework.http.converter.HttpMessageConverter;
@@ -52,10 +54,11 @@ import org.springframework.web.servlet.mvc.support.RedirectAttributes;
 import org.springframework.web.servlet.support.RequestContextUtils;
 
 /**
- * Resolves {@link HttpEntity} and {@link RequestEntity} method argument values
- * and also handles {@link HttpEntity} and {@link ResponseEntity} return values.
+ * Resolves {@link HttpEntity} and {@link RequestEntity} method argument values,
+ * as well as return values of type {@link HttpEntity}, {@link ResponseEntity},
+ * and {@link ProblemDetail}.
  *
- * <p>An {@link HttpEntity} return type has a specific purpose. Therefore this
+ * <p>An {@link HttpEntity} return type has a specific purpose. Therefore, this
  * handler should be configured ahead of handlers that support any return
  * value type annotated with {@code @ModelAttribute} or {@code @ResponseBody}
  * to ensure they don't take over.
@@ -82,9 +85,7 @@ public class HttpEntityMethodProcessor extends AbstractMessageConverterMethodPro
 	 * Suitable for resolving {@code HttpEntity} and handling {@code ResponseEntity}
 	 * without {@code Request~} or {@code ResponseBodyAdvice}.
 	 */
-	public HttpEntityMethodProcessor(List<HttpMessageConverter<?>> converters,
-			ContentNegotiationManager manager) {
-
+	public HttpEntityMethodProcessor(List<HttpMessageConverter<?>> converters, ContentNegotiationManager manager) {
 		super(converters, manager);
 	}
 
@@ -119,8 +120,9 @@ public class HttpEntityMethodProcessor extends AbstractMessageConverterMethodPro
 
 	@Override
 	public boolean supportsReturnType(MethodParameter returnType) {
-		return (HttpEntity.class.isAssignableFrom(returnType.getParameterType()) &&
-				!RequestEntity.class.isAssignableFrom(returnType.getParameterType()));
+		Class<?> type = returnType.getParameterType();
+		return ((HttpEntity.class.isAssignableFrom(type) && !RequestEntity.class.isAssignableFrom(type)) ||
+				ProblemDetail.class.isAssignableFrom(type));
 	}
 
 	@Override
@@ -177,8 +179,21 @@ public class HttpEntityMethodProcessor extends AbstractMessageConverterMethodPro
 		ServletServerHttpRequest inputMessage = createInputMessage(webRequest);
 		ServletServerHttpResponse outputMessage = createOutputMessage(webRequest);
 
-		Assert.isInstanceOf(HttpEntity.class, returnValue);
-		HttpEntity<?> httpEntity = (HttpEntity<?>) returnValue;
+		HttpEntity<?> httpEntity;
+		if (returnValue instanceof ProblemDetail detail) {
+			httpEntity = new ResponseEntity<>(returnValue, HttpHeaders.EMPTY, detail.getStatus());
+		}
+		else {
+			Assert.isInstanceOf(HttpEntity.class, returnValue);
+			httpEntity = (HttpEntity<?>) returnValue;
+		}
+
+		if (httpEntity.getBody() instanceof ProblemDetail detail) {
+			if (detail.getInstance() == null) {
+				URI path = URI.create(inputMessage.getServletRequest().getRequestURI());
+				detail.setInstance(path);
+			}
+		}
 
 		HttpHeaders outputHeaders = outputMessage.getHeaders();
 		HttpHeaders entityHeaders = httpEntity.getHeaders();

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/HttpEntityMethodProcessorMockTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -31,6 +31,7 @@ import java.util.Date;
 import java.util.Set;
 
 import jakarta.servlet.FilterChain;
+import jakarta.servlet.http.HttpServletResponse;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.mockito.ArgumentCaptor;
@@ -46,6 +47,7 @@ import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpOutputMessage;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
+import org.springframework.http.ProblemDetail;
 import org.springframework.http.RequestEntity;
 import org.springframework.http.ResponseEntity;
 import org.springframework.http.converter.HttpMessageConverter;
@@ -77,6 +79,8 @@ import static org.mockito.Mockito.reset;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.springframework.http.MediaType.APPLICATION_OCTET_STREAM;
+import static org.springframework.http.MediaType.APPLICATION_PROBLEM_JSON;
+import static org.springframework.http.MediaType.APPLICATION_PROBLEM_JSON_VALUE;
 import static org.springframework.http.MediaType.TEXT_PLAIN;
 import static org.springframework.web.servlet.HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE;
 
@@ -103,6 +107,8 @@ public class HttpEntityMethodProcessorMockTests {
 
 	private HttpMessageConverter<Object> resourceRegionMessageConverter;
 
+	private HttpMessageConverter<Object> jsonMessageConverter;
+
 	private MethodParameter paramHttpEntity;
 
 	private MethodParameter paramRequestEntity;
@@ -123,6 +129,8 @@ public class HttpEntityMethodProcessorMockTests {
 
 	private MethodParameter returnTypeInt;
 
+	private MethodParameter returnTypeProblemDetail;
+
 	private ModelAndViewContainer mavContainer;
 
 	private MockHttpServletRequest servletRequest;
@@ -147,8 +155,12 @@ public class HttpEntityMethodProcessorMockTests {
 		given(resourceRegionMessageConverter.getSupportedMediaTypes()).willReturn(Collections.singletonList(MediaType.ALL));
 		given(resourceRegionMessageConverter.getSupportedMediaTypes(any())).willReturn(Collections.singletonList(MediaType.ALL));
 
+		jsonMessageConverter = mock(HttpMessageConverter.class);
+		given(jsonMessageConverter.getSupportedMediaTypes()).willReturn(Collections.singletonList(MediaType.APPLICATION_PROBLEM_JSON));
+		given(jsonMessageConverter.getSupportedMediaTypes(any())).willReturn(Collections.singletonList(MediaType.APPLICATION_PROBLEM_JSON));
+
 		processor = new HttpEntityMethodProcessor(Arrays.asList(
-				stringHttpMessageConverter, resourceMessageConverter, resourceRegionMessageConverter));
+				stringHttpMessageConverter, resourceMessageConverter, resourceRegionMessageConverter, jsonMessageConverter));
 
 		Method handle1 = getClass().getMethod("handle1", HttpEntity.class, ResponseEntity.class,
 				Integer.TYPE, RequestEntity.class);
@@ -163,6 +175,7 @@ public class HttpEntityMethodProcessorMockTests {
 		returnTypeHttpEntitySubclass = new MethodParameter(getClass().getMethod("handle2x", HttpEntity.class), -1);
 		returnTypeInt = new MethodParameter(getClass().getMethod("handle3"), -1);
 		returnTypeResponseEntityResource = new MethodParameter(getClass().getMethod("handle5"), -1);
+		returnTypeProblemDetail = new MethodParameter(getClass().getMethod("handle6"), -1);
 
 		mavContainer = new ModelAndViewContainer();
 		servletRequest = new MockHttpServletRequest("GET", "/foo");
@@ -184,6 +197,7 @@ public class HttpEntityMethodProcessorMockTests {
 		assertThat(processor.supportsReturnType(returnTypeResponseEntity)).as("ResponseEntity return type not supported").isTrue();
 		assertThat(processor.supportsReturnType(returnTypeHttpEntity)).as("HttpEntity return type not supported").isTrue();
 		assertThat(processor.supportsReturnType(returnTypeHttpEntitySubclass)).as("Custom HttpEntity subclass not supported").isTrue();
+		assertThat(processor.supportsReturnType(returnTypeProblemDetail)).isTrue();
 		assertThat(processor.supportsReturnType(paramRequestEntity)).as("RequestEntity parameter supported").isFalse();
 		assertThat(processor.supportsReturnType(returnTypeInt)).as("non-ResponseBody return type supported").isFalse();
 	}
@@ -268,6 +282,36 @@ public class HttpEntityMethodProcessorMockTests {
 		verify(stringHttpMessageConverter).write(eq(body), eq(accepted), isA(HttpOutputMessage.class));
 	}
 
+	@Test
+	public void shouldHandleProblemDetail() throws Exception {
+		ProblemDetail problemDetail = ProblemDetail.forStatus(HttpStatus.BAD_REQUEST);
+		servletRequest.addHeader("Accept", APPLICATION_PROBLEM_JSON_VALUE);
+		given(jsonMessageConverter.canWrite(ProblemDetail.class, APPLICATION_PROBLEM_JSON)).willReturn(true);
+
+		processor.handleReturnValue(problemDetail, returnTypeProblemDetail, mavContainer, webRequest);
+
+		assertThat(mavContainer.isRequestHandled()).isTrue();
+		assertThat(webRequest.getNativeResponse(HttpServletResponse.class).getStatus()).isEqualTo(400);
+		verify(jsonMessageConverter).write(eq(problemDetail), eq(APPLICATION_PROBLEM_JSON), isA(HttpOutputMessage.class));
+
+		assertThat(problemDetail).isNotNull()
+				.extracting(ProblemDetail::getInstance).isNotNull()
+				.extracting(URI::toString)
+				.as("Instance was not set to the request path")
+				.isEqualTo(servletRequest.getRequestURI());
+
+
+		// But if instance is set, it should be respected
+		problemDetail.setInstance(URI.create("/something/else"));
+		processor.handleReturnValue(problemDetail, returnTypeProblemDetail, mavContainer, webRequest);
+
+		assertThat(problemDetail).isNotNull()
+				.extracting(ProblemDetail::getInstance).isNotNull()
+				.extracting(URI::toString)
+				.as("Instance was not set to the request path")
+				.isEqualTo("/something/else");
+	}
+
 	@Test
 	public void shouldHandleReturnValueWithProducibleMediaType() throws Exception {
 		String body = "Foo";
@@ -797,6 +841,11 @@ public class HttpEntityMethodProcessorMockTests {
 		return null;
 	}
 
+	@SuppressWarnings("unused")
+	public ProblemDetail handle6() {
+		return null;
+	}
+
 	@SuppressWarnings("unused")
 	public static class CustomHttpEntity extends HttpEntity<Object> {
 	}