#786 - Implement vendor neutral error handling with RFC-7807.

src/main/java/org/springframework/hateoas/MediaTypes.java

@@ -76,8 +76,7 @@ public class MediaTypes {
 	 * Public constant media type for {@code application/vnd.amundsen-uber+json}.
 	 */
 	public static final MediaType UBER_JSON = MediaType.parseMediaType(UBER_JSON_VALUE);
-
-
+	
 	/**
 	 * A String equivalent of {@link MediaTypes#VND_ERROR_JSON}.
 	 */
@@ -87,4 +86,14 @@ public class MediaTypes {
 	 * Public constant media type for {@code application/vnd.error+json}.
 	 */
 	public static final MediaType VND_ERROR_JSON = MediaType.valueOf(VND_ERROR_JSON_VALUE);
+
+	/**
+	 * A String equivalent of {@link MediaTypes#PROBLEM_JSON_VALUE}.
+	 */
+	public static final String PROBLEM_JSON_VALUE = "application/problem+json";
+
+	/**
+	 * Public constant media type for {@code application/problem+json}.
+	 */
+	public static final MediaType PROBLEM_JSON = MediaType.parseMediaType(PROBLEM_JSON_VALUE);
 }

src/main/java/org/springframework/hateoas/mediatype/problem/Problem.java

@@ -0,0 +1,161 @@
+/*
+ * Copyright 2019 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.hateoas.mediatype.problem;
+
+import java.net.URI;
+import java.util.Objects;
+
+import org.springframework.http.HttpStatus;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.JsonInclude.Include;
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+/**
+ * Encapsulation of an RFC-7807 {@literal Problem} code. While it complies out-of-the-box, it may also be extended to
+ * support domain-specific details.
+ * 
+ * @author Greg Turnquist
+ */
+public class Problem<T extends Problem<? extends T>> {
+
+	private URI type;
+	private String title;
+	private HttpStatus status;
+	private String detail;
+	private URI instance;
+
+	public Problem() {
+		this(null, null, null, null, null);
+	}
+
+	public Problem(URI type, String title, HttpStatus status, String detail, URI instance) {
+
+		this.type = type;
+		this.title = title;
+		this.status = status;
+		this.detail = detail;
+		this.instance = instance;
+	}
+
+	@JsonCreator
+	public Problem(@JsonProperty("type") URI type, @JsonProperty("title") String title,
+			@JsonProperty("status") int status, @JsonProperty("detail") String detail,
+			@JsonProperty("instance") URI instance) {
+		this(type, title, HttpStatus.resolve(status), detail, instance);
+	}
+
+	/**
+	 * A {@link Problem} that reflects an {@link HttpStatus} code.
+	 *
+	 * @see https://tools.ietf.org/html/rfc7807#section-4.2
+	 */
+	public Problem(HttpStatus httpStatus) {
+		this(URI.create("about:blank"), httpStatus.getReasonPhrase(), httpStatus, null, null);
+	}
+
+	@SuppressWarnings("unchecked")
+	public T withType(URI type) {
+		this.type = type;
+		return (T) this;
+	}
+
+	@SuppressWarnings("unchecked")
+	public T withTitle(String title) {
+		this.title = title;
+		return (T) this;
+	}
+
+	@SuppressWarnings("unchecked")
+	public T withStatus(HttpStatus status) {
+		this.status = status;
+		return (T) this;
+	}
+
+	@SuppressWarnings("unchecked")
+	public T withDetail(String detail) {
+		this.detail = detail;
+		return (T) this;
+	}
+
+	@SuppressWarnings("unchecked")
+	public T withInstance(URI instance) {
+		this.instance = instance;
+		return (T) this;
+	}
+
+	@JsonInclude(Include.NON_NULL)
+	public URI getType() {
+		return this.type;
+	}
+
+	@JsonInclude(Include.NON_NULL)
+	public String getTitle() {
+		return this.title;
+	}
+
+	@JsonInclude(Include.NON_NULL)
+	public Integer getStatus() {
+		if (status != null) {
+			return status.value();
+		}
+
+		return null;
+	}
+
+	@JsonInclude(Include.NON_NULL)
+	public String getDetail() {
+		return detail;
+	}
+
+	@JsonInclude(Include.NON_NULL)
+	public URI getInstance() {
+		return instance;
+	}
+
+	@Override
+	public boolean equals(Object o) {
+
+		if (this == o)
+			return true;
+		if (o == null || getClass() != o.getClass())
+			return false;
+		Problem problem = (Problem) o;
+		return Objects.equals(type, problem.type) && //
+				Objects.equals(title, problem.title) && //
+				status == problem.status && //
+				Objects.equals(detail, problem.detail) && //
+				Objects.equals(instance, problem.instance); //
+	}
+
+	@Override
+	public int hashCode() {
+		return Objects.hash(type, title, status, detail, instance);
+	}
+
+	@Override
+	public String toString() {
+
+		return "Problem{" + //
+				"type=" + type + //
+				", title='" + title + '\'' + //
+				", status=" + status + //
+				", detail='" + detail + '\'' + //
+				", instance=" + instance + //
+				'}';
+	}
+}

src/main/java/org/springframework/hateoas/mediatype/problem/package-info.java

@@ -0,0 +1,5 @@
+/**
+ * Value objects to build Problem representations.
+ */
+@org.springframework.lang.NonNullApi
+package org.springframework.hateoas.mediatype.problem;

src/test/java/org/springframework/hateoas/mediatype/hal/forms/HalFormsWebFluxIntegrationTest.java

@@ -15,10 +15,13 @@
  */
 package org.springframework.hateoas.mediatype.hal.forms;
 
+import static org.assertj.core.api.Assertions.*;
 import static org.hamcrest.CoreMatchers.*;
 import static org.hamcrest.collection.IsCollectionWithSize.*;
 import static org.springframework.hateoas.support.JsonPathUtils.*;
 
+import java.net.URI;
+
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
@@ -31,9 +34,11 @@ import org.springframework.hateoas.MediaTypes;
 import org.springframework.hateoas.config.EnableHypermediaSupport;
 import org.springframework.hateoas.config.EnableHypermediaSupport.HypermediaType;
 import org.springframework.hateoas.config.WebClientConfigurer;
+import org.springframework.hateoas.mediatype.problem.Problem;
 import org.springframework.hateoas.support.MappingUtils;
 import org.springframework.hateoas.support.WebFluxEmployeeController;
 import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatus;
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.test.context.junit.jupiter.SpringExtension;
 import org.springframework.test.context.web.WebAppConfiguration;
@@ -128,6 +133,23 @@ class HalFormsWebFluxIntegrationTest {
 				.expectHeader().valueEquals(HttpHeaders.LOCATION, "http://localhost/employees/2");
 	}
 
+	@Test
+	void problemReturningControllerMethod() {
+
+		Problem<?> problem = this.testClient.get().uri("http://localhost/employees/problem").accept(MediaTypes.PROBLEM_JSON) //
+				.exchange() //
+				.expectStatus().isBadRequest() //
+				.expectHeader().contentType(MediaTypes.PROBLEM_JSON) //
+				.expectBody(Problem.class) //
+				.returnResult().getResponseBody();
+
+		assertThat(problem).isNotNull();
+		assertThat(problem.getType()).isEqualTo(URI.create("http://example.com/problem"));
+		assertThat(problem.getTitle()).isEqualTo("Employee-based problem");
+		assertThat(problem.getStatus()).isEqualTo(HttpStatus.BAD_REQUEST.value());
+		assertThat(problem.getDetail()).isEqualTo("This is a test case");
+	}
+
 	@Configuration
 	@EnableWebFlux
 	@EnableHypermediaSupport(type = { HypermediaType.HAL_FORMS })

src/test/java/org/springframework/hateoas/mediatype/problem/JacksonSerializationTest.java

@@ -0,0 +1,345 @@
+package org.springframework.hateoas.mediatype.problem;
+
+import static org.assertj.core.api.Assertions.*;
+
+import java.io.IOException;
+import java.net.URI;
+import java.util.List;
+import java.util.Objects;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.hateoas.support.MappingUtils;
+import org.springframework.http.HttpStatus;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.databind.DeserializationFeature;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+
+/**
+ * @author Greg Turnquist
+ */
+class JacksonSerializationTest {
+
+	ObjectMapper mapper;
+
+	@BeforeEach
+	void setUp() {
+
+		this.mapper = new ObjectMapper();
+		this.mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
+		this.mapper.configure(SerializationFeature.INDENT_OUTPUT, true);
+	}
+
+	@Test
+	void httpStatusProblemSerialize() throws IOException {
+
+		Problem problem = new Problem(HttpStatus.NOT_FOUND);
+
+		String actual = this.mapper.writeValueAsString(problem);
+		assertThat(actual).isEqualTo(MappingUtils.read(new ClassPathResource("http-status-problem.json", getClass())));
+	}
+
+	@Test
+	void httpStatusProblemDeserialize() throws IOException {
+
+		String expected = MappingUtils.read(new ClassPathResource("http-status-problem.json", getClass()));
+
+		Problem<?> actual = this.mapper.readValue(expected, Problem.class);
+
+		assertThat(actual.getType()).isEqualTo(URI.create("about:blank"));
+		assertThat(actual.getTitle()).isEqualTo("Not Found");
+		assertThat(actual.getStatus()).isEqualTo(HttpStatus.NOT_FOUND.value());
+		assertThat(actual.getDetail()).isNull();
+		assertThat(actual.getInstance()).isNull();
+	}
+
+	@Test
+	void typeOnlySerialize() throws IOException {
+
+		Problem problem = new Problem().withType(URI.create("http://example.com/problem-details"));
+
+		String actual = this.mapper.writeValueAsString(problem);
+		assertThat(actual).isEqualTo(MappingUtils.read(new ClassPathResource("type-only.json", getClass())));
+	}
+
+	@Test
+	void typeOnlyDeserialize() throws IOException {
+
+		String expected = MappingUtils.read(new ClassPathResource("type-only.json", getClass()));
+
+		Problem<?> actual = this.mapper.readValue(expected, Problem.class);
+
+		assertThat(actual.getType()).isEqualTo(URI.create("http://example.com/problem-details"));
+		assertThat(actual.getTitle()).isNull();
+		assertThat(actual.getStatus()).isNull();
+		assertThat(actual.getDetail()).isNull();
+		assertThat(actual.getInstance()).isNull();
+	}
+
+	@Test
+	void titleOnlySerialize() throws IOException {
+
+		Problem problem = new Problem().withTitle("test title");
+
+		String actual = this.mapper.writeValueAsString(problem);
+		assertThat(actual).isEqualTo(MappingUtils.read(new ClassPathResource("title-only.json", getClass())));
+	}
+
+	@Test
+	void titleOnlyDeserialize() throws IOException {
+
+		String expected = MappingUtils.read(new ClassPathResource("title-only.json", getClass()));
+
+		Problem<?> actual = this.mapper.readValue(expected, Problem.class);
+
+		assertThat(actual.getType()).isNull();
+		assertThat(actual.getTitle()).isEqualTo("test title");
+		assertThat(actual.getStatus()).isNull();
+		assertThat(actual.getDetail()).isNull();
+		assertThat(actual.getInstance()).isNull();
+	}
+
+	@Test
+	void statusOnlySerialize() throws IOException {
+
+		Problem problem = new Problem().withStatus(HttpStatus.BAD_GATEWAY);
+
+		String actual = this.mapper.writeValueAsString(problem);
+		assertThat(actual).isEqualTo(MappingUtils.read(new ClassPathResource("status-only.json", getClass())));
+	}
+
+	@Test
+	void statusOnlyDeserialize() throws IOException {
+
+		String expected = MappingUtils.read(new ClassPathResource("status-only.json", getClass()));
+
+		Problem<?> actual = this.mapper.readValue(expected, Problem.class);
+
+		assertThat(actual.getType()).isNull();
+		assertThat(actual.getTitle()).isNull();
+		assertThat(actual.getStatus()).isEqualTo(502);
+		assertThat(actual.getDetail()).isNull();
+		assertThat(actual.getInstance()).isNull();
+	}
+
+	@Test
+	void detailOnlySerialize() throws IOException {
+
+		Problem problem = new Problem().withDetail("test detail");
+
+		String actual = this.mapper.writeValueAsString(problem);
+		assertThat(actual).isEqualTo(MappingUtils.read(new ClassPathResource("detail-only.json", getClass())));
+	}
+
+	@Test
+	void detailOnlyDeserialize() throws IOException {
+
+		String expected = MappingUtils.read(new ClassPathResource("detail-only.json", getClass()));
+
+		Problem<?> actual = this.mapper.readValue(expected, Problem.class);
+
+		assertThat(actual.getType()).isNull();
+		assertThat(actual.getTitle()).isNull();
+		assertThat(actual.getStatus()).isNull();
+		assertThat(actual.getDetail()).isEqualTo("test detail");
+		assertThat(actual.getInstance()).isNull();
+	}
+
+	@Test
+	void instanceOnlySerialize() throws IOException {
+
+		Problem problem = new Problem().withInstance(URI.create("http://example.com/employees/1471"));
+
+		String actual = this.mapper.writeValueAsString(problem);
+		assertThat(actual).isEqualTo(MappingUtils.read(new ClassPathResource("instance-only.json", getClass())));
+	}
+
+	@Test
+	void instanceOnlyDeserialize() throws IOException {
+
+		String expected = MappingUtils.read(new ClassPathResource("instance-only.json", getClass()));
+
+		Problem<?> actual = this.mapper.readValue(expected, Problem.class);
+
+		assertThat(actual.getType()).isNull();
+		assertThat(actual.getTitle()).isNull();
+		assertThat(actual.getStatus()).isNull();
+		assertThat(actual.getDetail()).isNull();
+		assertThat(actual.getInstance()).isEqualTo(URI.create("http://example.com/employees/1471"));
+	}
+
+	@Test
+	void extensionSerialize() throws IOException {
+
+		AccountProblem problem = new AccountProblem() //
+				.withType(URI.create("https://example.com/probs/out-of-credit")) //
+				.withTitle("You do not have enough credit.") //
+				.withDetail("Your current balance is 30, but that costs 50.") //
+				.withInstance(URI.create("/account/12345/msgs/abc")) //
+				.withBalance(30) //
+				.withAccounts("/account/12345", "/account/67890");
+
+		String actual = this.mapper.writeValueAsString(problem);
+		assertThat(actual).isEqualTo(MappingUtils.read(new ClassPathResource("extension.json", getClass())));
+	}
+
+	@Test
+	void extensionDeserialize() throws IOException {
+
+		String expected = MappingUtils.read(new ClassPathResource("extension.json", getClass()));
+
+		AccountProblem actual = this.mapper.readValue(expected, AccountProblem.class);
+
+		assertThat(actual.getType()).isEqualTo(URI.create("https://example.com/probs/out-of-credit"));
+		assertThat(actual.getTitle()).isEqualTo("You do not have enough credit.");
+		assertThat(actual.getStatus()).isNull();
+		assertThat(actual.getDetail()).isEqualTo("Your current balance is 30, but that costs 50.");
+		assertThat(actual.getInstance()).isEqualTo(URI.create("/account/12345/msgs/abc"));
+		assertThat(actual.getBalance()).isEqualTo(30);
+		assertThat(actual.getAccounts()).containsExactlyInAnyOrder("/account/12345", "/account/67890");
+	}
+
+	@Test
+	void reference1Deserialize() throws IOException {
+
+		AccountProblem accountProblem = this.mapper
+				.readValue(MappingUtils.read(new ClassPathResource("reference-1.json", getClass())), AccountProblem.class);
+
+		assertThat(accountProblem.getType()).isEqualTo(URI.create("https://example.com/probs/out-of-credit"));
+		assertThat(accountProblem.getTitle()).isEqualTo("You do not have enough credit.");
+		assertThat(accountProblem.getDetail()).isEqualTo("Your current balance is 30, but that costs 50.");
+		assertThat(accountProblem.getInstance()).isEqualTo(URI.create("/account/12345/msgs/abc"));
+		assertThat(accountProblem.getBalance()).isEqualTo(30);
+		assertThat(accountProblem.getAccounts()).containsExactlyInAnyOrder("/account/12345", "/account/67890");
+	}
+
+	@Test
+	void reference2Deserialize() throws IOException {
+
+		InvalidParameters invalidParameters = this.mapper
+				.readValue(MappingUtils.read(new ClassPathResource("reference-2.json", getClass())), InvalidParameters.class);
+
+		assertThat(invalidParameters.getType()).isEqualTo(URI.create("https://example.net/validation-error"));
+		assertThat(invalidParameters.getTitle()).isEqualTo("Your request parameters didn't validate.");
+		assertThat(invalidParameters.getDetail()).isNull();
+		assertThat(invalidParameters.getInstance()).isNull();
+		assertThat(invalidParameters.getInvalidParameters()).hasSize(2);
+		assertThat(invalidParameters.getInvalidParameters()).containsExactly(
+				new InvalidParameter("age", "must be a positive integer"),
+				new InvalidParameter("color", "must be 'green', 'red' or 'blue'"));
+	}
+
+	/**
+	 * First reference domain definition.
+	 *
+	 * @see https://tools.ietf.org/html/rfc7807#section-3
+	 */
+	private static class AccountProblem extends Problem<AccountProblem> {
+
+		private int balance;
+		private String[] accounts;
+
+		AccountProblem() {
+			super();
+		}
+
+		AccountProblem withBalance(int balance) {
+
+			this.balance = balance;
+			return this;
+		}
+
+		AccountProblem withAccounts(String... accounts) {
+
+			this.accounts = accounts;
+			return this;
+		}
+
+		public int getBalance() {
+			return this.balance;
+		}
+
+		public String[] getAccounts() {
+			return this.accounts;
+		}
+	}
+
+	/**
+	 * Second reference domain definition.
+	 *
+	 * @see https://tools.ietf.org/html/rfc7807#section-3
+	 */
+	private static class InvalidParameters extends Problem<InvalidParameters> {
+
+		private List<InvalidParameter> invalidParameters;
+
+		@JsonCreator
+		public InvalidParameters(@JsonProperty("invalid-params") List<InvalidParameter> invalidParameters) {
+
+			super();
+			this.invalidParameters = invalidParameters;
+		}
+
+		public List<InvalidParameter> getInvalidParameters() {
+			return invalidParameters;
+		}
+	}
+
+	private static class InvalidParameter {
+
+		private String name;
+		private String reason;
+
+		InvalidParameter() {}
+
+		InvalidParameter(String name, String reason) {
+
+			this.name = name;
+			this.reason = reason;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+
+		public String getReason() {
+			return reason;
+		}
+
+		public void setReason(String reason) {
+			this.reason = reason;
+		}
+
+		@Override
+		public boolean equals(Object o) {
+
+			if (this == o)
+				return true;
+			if (o == null || getClass() != o.getClass())
+				return false;
+			InvalidParameter that = (InvalidParameter) o;
+			return Objects.equals(name, that.name) && Objects.equals(reason, that.reason);
+		}
+
+		@Override
+		public int hashCode() {
+			return Objects.hash(name, reason);
+		}
+
+		@Override
+		public String toString() {
+			return "InvalidParameter{" + //
+					"name='" + name + '\'' + //
+					", reason='" + reason + '\'' + //
+					'}';
+		}
+	}
+}

src/test/java/org/springframework/hateoas/server/mvc/RepresentationModelProcessorIntegrationTest.java

@@ -16,6 +16,7 @@
 package org.springframework.hateoas.server.mvc;
 
 import static org.assertj.core.api.AssertionsForClassTypes.*;
+import static org.hamcrest.CoreMatchers.*;
 import static org.springframework.hateoas.MediaTypes.*;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;
@@ -42,6 +43,7 @@ import org.springframework.hateoas.server.RepresentationModelProcessor;
 import org.springframework.hateoas.support.Employee;
 import org.springframework.hateoas.support.WebMvcEmployeeController;
 import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatus;
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.test.context.junit.jupiter.SpringExtension;
 import org.springframework.test.context.web.WebAppConfiguration;
@@ -105,6 +107,19 @@ public class RepresentationModelProcessorIntegrationTest {
 		assertThat(wildcardProcessor.isTriggered()).isTrue();
 	}
 
+	@Test
+	public void problemReturningControllerMethod() throws Exception {
+
+		this.mockMvc.perform(get("/employees/problem").accept(PROBLEM_JSON)) //
+				.andExpect(content().contentType(PROBLEM_JSON)) //
+				.andExpect(status().is(HttpStatus.BAD_REQUEST.value())) //
+				.andExpect(jsonPath("$.type", is("http://example.com/problem"))) //
+				.andExpect(jsonPath("$.title", is("Employee-based problem"))) //
+				.andExpect(jsonPath("$.status", is(HttpStatus.BAD_REQUEST.value()))) //
+				.andExpect(jsonPath("$.detail", is("This is a test case")));
+
+	}
+
 	@Test
 	public void entityModelProcessorShouldWork() throws Exception {
 

src/test/java/org/springframework/hateoas/support/WebFluxEmployeeController.java

@@ -21,14 +21,16 @@ import static org.springframework.hateoas.mediatype.alps.Alps.*;
 import static org.springframework.hateoas.server.reactive.WebFluxLinkBuilder.*;
 import static reactor.function.TupleUtils.*;
 
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+import java.net.URI;
 import java.util.Collections;
 import java.util.Map;
 import java.util.Optional;
 import java.util.TreeMap;
 import java.util.stream.Collectors;
 
-import reactor.core.publisher.Flux;
-import reactor.core.publisher.Mono;
 import org.springframework.hateoas.Affordance;
 import org.springframework.hateoas.CollectionModel;
 import org.springframework.hateoas.EntityModel;
@@ -40,7 +42,9 @@ import org.springframework.hateoas.mediatype.alps.Descriptor;
 import org.springframework.hateoas.mediatype.alps.Ext;
 import org.springframework.hateoas.mediatype.alps.Format;
 import org.springframework.hateoas.mediatype.alps.Type;
+import org.springframework.hateoas.mediatype.problem.Problem;
 import org.springframework.hateoas.server.reactive.WebFluxLinkBuilder;
+import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PatchMapping;
@@ -210,4 +214,14 @@ public class WebFluxEmployeeController {
 						.collect(Collectors.toList()))
 				.build();
 	}
+
+	@GetMapping("/employees/problem")
+	public ResponseEntity<?> problem() {
+
+		return ResponseEntity.badRequest().body(new Problem() //
+				.withType(URI.create("http://example.com/problem")) //
+				.withTitle("Employee-based problem") //
+				.withStatus(HttpStatus.BAD_REQUEST) //
+				.withDetail("This is a test case"));
+	}
 }

src/test/java/org/springframework/hateoas/support/WebMvcEmployeeController.java

@@ -20,6 +20,7 @@ import static org.springframework.hateoas.mediatype.PropertyUtils.*;
 import static org.springframework.hateoas.mediatype.alps.Alps.*;
 import static org.springframework.hateoas.server.mvc.WebMvcLinkBuilder.*;
 
+import java.net.URI;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -38,6 +39,8 @@ import org.springframework.hateoas.mediatype.alps.Descriptor;
 import org.springframework.hateoas.mediatype.alps.Ext;
 import org.springframework.hateoas.mediatype.alps.Format;
 import org.springframework.hateoas.mediatype.alps.Type;
+import org.springframework.hateoas.mediatype.problem.Problem;
+import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PatchMapping;
@@ -211,4 +214,14 @@ public class WebMvcEmployeeController {
 				.build();
 	}
 	// end::alps-profile[]
+
+	@GetMapping("/employees/problem")
+	public ResponseEntity<?> problem() {
+
+		return ResponseEntity.badRequest().body(new Problem<>() //
+				.withType(URI.create("http://example.com/problem")) //
+				.withTitle("Employee-based problem") //
+				.withStatus(HttpStatus.BAD_REQUEST) //
+				.withDetail("This is a test case"));
+	}
 }

src/test/resources/org/springframework/hateoas/mediatype/problem/detail-only.json

@@ -0,0 +1,3 @@
+{
+  "detail" : "test detail"
+}

src/test/resources/org/springframework/hateoas/mediatype/problem/extension.json

@@ -0,0 +1,8 @@
+{
+  "type" : "https://example.com/probs/out-of-credit",
+  "title" : "You do not have enough credit.",
+  "detail" : "Your current balance is 30, but that costs 50.",
+  "instance" : "/account/12345/msgs/abc",
+  "balance" : 30,
+  "accounts" : [ "/account/12345", "/account/67890" ]
+}

src/test/resources/org/springframework/hateoas/mediatype/problem/http-status-problem.json

@@ -0,0 +1,5 @@
+{
+  "type" : "about:blank",
+  "title" : "Not Found",
+  "status" : 404
+}

src/test/resources/org/springframework/hateoas/mediatype/problem/instance-only.json

@@ -0,0 +1,3 @@
+{
+  "instance" : "http://example.com/employees/1471"
+}

src/test/resources/org/springframework/hateoas/mediatype/problem/reference-1.json

@@ -0,0 +1,9 @@
+{
+  "type": "https://example.com/probs/out-of-credit",
+  "title": "You do not have enough credit.",
+  "detail": "Your current balance is 30, but that costs 50.",
+  "instance": "/account/12345/msgs/abc",
+  "balance": 30,
+  "accounts": ["/account/12345",
+    "/account/67890"]
+}

src/test/resources/org/springframework/hateoas/mediatype/problem/reference-2.json

@@ -0,0 +1,12 @@
+{
+  "type": "https://example.net/validation-error",
+  "title": "Your request parameters didn't validate.",
+  "invalid-params": [ {
+    "name": "age",
+    "reason": "must be a positive integer"
+  },
+    {
+      "name": "color",
+      "reason": "must be 'green', 'red' or 'blue'"}
+  ]
+}

src/test/resources/org/springframework/hateoas/mediatype/problem/status-only.json

@@ -0,0 +1,3 @@
+{
+  "status" : 502
+}

src/test/resources/org/springframework/hateoas/mediatype/problem/title-only.json

@@ -0,0 +1,3 @@
+{
+  "title" : "test title"
+}

src/test/resources/org/springframework/hateoas/mediatype/problem/type-only.json

@@ -0,0 +1,3 @@
+{
+  "type" : "http://example.com/problem-details"
+}