Allow an operation to specify the media types that it produces

Closes gh-10118

spring-boot/src/main/java/org/springframework/boot/endpoint/DeleteOperation.java

@@ -26,6 +26,7 @@ import java.lang.annotation.Target;
  * Identifies a method on an {@link Endpoint} as being a delete operation.
  *
  * @author Stephane Nicoll
+ * @author Andy Wilkinson
  * @since 2.0.0
  */
 @Target(ElementType.METHOD)
@@ -33,4 +34,11 @@ import java.lang.annotation.Target;
 @Documented
 public @interface DeleteOperation {
 
+	/**
+	 * The media type of the result of the operation.
+	 *
+	 * @return the media type
+	 */
+	String[] produces() default {};
+
 }

spring-boot/src/main/java/org/springframework/boot/endpoint/ReadOperation.java

@@ -33,4 +33,11 @@ import java.lang.annotation.Target;
 @Documented
 public @interface ReadOperation {
 
+	/**
+	 * The media type of the result of the operation.
+	 *
+	 * @return the media type
+	 */
+	String[] produces() default {};
+
 }

spring-boot/src/main/java/org/springframework/boot/endpoint/WriteOperation.java

@@ -33,4 +33,11 @@ import java.lang.annotation.Target;
 @Documented
 public @interface WriteOperation {
 
+	/**
+	 * The media type of the result of the operation.
+	 *
+	 * @return the media type
+	 */
+	String[] produces() default {};
+
 }

spring-boot/src/main/java/org/springframework/boot/endpoint/web/WebAnnotationEndpointDiscoverer.java

@@ -18,6 +18,7 @@ package org.springframework.boot.endpoint.web;
 
 import java.lang.reflect.Method;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
@@ -134,7 +135,8 @@ public class WebAnnotationEndpointDiscoverer extends
 			OperationRequestPredicate requestPredicate = new OperationRequestPredicate(
 					determinePath(endpointId, method), httpMethod,
 					determineConsumedMediaTypes(httpMethod, method),
-					determineProducedMediaTypes(method));
+					determineProducedMediaTypes(
+							operationAttributes.getStringArray("produces"), method));
 			OperationInvoker invoker = new ReflectiveOperationInvoker(
 					this.parameterMapper, target, method);
 			if (timeToLive > 0) {
@@ -171,7 +173,11 @@ public class WebAnnotationEndpointDiscoverer extends
 			return Collections.emptyList();
 		}
 
-		private Collection<String> determineProducedMediaTypes(Method method) {
+		private Collection<String> determineProducedMediaTypes(String[] produces,
+				Method method) {
+			if (produces.length > 0) {
+				return Arrays.asList(produces);
+			}
 			if (Void.class.equals(method.getReturnType())
 					|| void.class.equals(method.getReturnType())) {
 				return Collections.emptyList();

spring-boot/src/test/java/org/springframework/boot/endpoint/web/AbstractWebEndpointIntegrationTests.java

@@ -254,6 +254,14 @@ public abstract class AbstractWebEndpointIntegrationTests<T extends Configurable
 						.isEqualTo("alpha"));
 	}
 
+	@Test
+	public void readOperationWithCustomMediaType() {
+		load(CustomMediaTypesEndpointConfiguration.class,
+				(client) -> client.get().uri("/custommediatypes").exchange()
+						.expectStatus().isOk().expectHeader()
+						.valueMatches("Content-Type", "text/plain(;charset=.*)?"));
+	}
+
 	protected abstract T createApplicationContext(Class<?>... config);
 
 	protected abstract int getPort(T context);
@@ -422,6 +430,17 @@ public abstract class AbstractWebEndpointIntegrationTests<T extends Configurable
 
 	}
 
+	@Configuration
+	@Import(BaseConfiguration.class)
+	static class CustomMediaTypesEndpointConfiguration {
+
+		@Bean
+		public CustomMediaTypesEndpoint customMediaTypesEndpoint() {
+			return new CustomMediaTypesEndpoint();
+		}
+
+	}
+
 	@Endpoint(id = "test")
 	static class TestEndpoint {
 
@@ -580,6 +599,16 @@ public abstract class AbstractWebEndpointIntegrationTests<T extends Configurable
 
 	}
 
+	@Endpoint(id = "custommediatypes")
+	static class CustomMediaTypesEndpoint {
+
+		@ReadOperation(produces = "text/plain")
+		public String read() {
+			return "read";
+		}
+
+	}
+
 	public interface EndpointDelegate {
 
 		void write();

spring-boot/src/test/java/org/springframework/boot/endpoint/web/WebAnnotationEndpointDiscovererTests.java

@@ -36,6 +36,7 @@ import org.junit.rules.ExpectedException;
 import org.springframework.boot.endpoint.CachingConfiguration;
 import org.springframework.boot.endpoint.CachingOperationInvoker;
 import org.springframework.boot.endpoint.ConversionServiceOperationParameterMapper;
+import org.springframework.boot.endpoint.DeleteOperation;
 import org.springframework.boot.endpoint.Endpoint;
 import org.springframework.boot.endpoint.EndpointExposure;
 import org.springframework.boot.endpoint.EndpointInfo;
@@ -216,6 +217,24 @@ public class WebAnnotationEndpointDiscovererTests {
 		});
 	}
 
+	@Test
+	public void operationCanProduceCustomMediaTypes() {
+		load(CustomMediaTypesEndpointConfiguration.class, (discoverer) -> {
+			Map<String, EndpointInfo<WebEndpointOperation>> endpoints = mapEndpoints(
+					discoverer.discoverEndpoints());
+			assertThat(endpoints).containsOnlyKeys("custommediatypes");
+			EndpointInfo<WebEndpointOperation> endpoint = endpoints
+					.get("custommediatypes");
+			assertThat(requestPredicates(endpoint)).has(requestPredicates(
+					path("custommediatypes").httpMethod(WebEndpointHttpMethod.GET)
+							.consumes().produces("text/plain"),
+					path("custommediatypes").httpMethod(WebEndpointHttpMethod.POST)
+							.consumes().produces("a/b", "c/d"),
+					path("custommediatypes").httpMethod(WebEndpointHttpMethod.DELETE)
+							.consumes().produces("text/plain")));
+		});
+	}
+
 	private void load(Class<?> configuration,
 			Consumer<WebAnnotationEndpointDiscoverer> consumer) {
 		this.load((id) -> null, configuration, consumer);
@@ -415,6 +434,27 @@ public class WebAnnotationEndpointDiscovererTests {
 
 	}
 
+	@Endpoint(id = "custommediatypes")
+	static class CustomMediaTypesEndpoint {
+
+		@ReadOperation(produces = "text/plain")
+		public String read() {
+			return "read";
+		}
+
+		@WriteOperation(produces = { "a/b", "c/d" })
+		public String write() {
+			return "write";
+
+		}
+
+		@DeleteOperation(produces = "text/plain")
+		public String delete() {
+			return "delete";
+		}
+
+	}
+
 	@Configuration
 	static class MultipleEndpointsConfiguration {
 
@@ -578,6 +618,17 @@ public class WebAnnotationEndpointDiscovererTests {
 
 	}
 
+	@Configuration
+	@Import(BaseConfiguration.class)
+	static class CustomMediaTypesEndpointConfiguration {
+
+		@Bean
+		public CustomMediaTypesEndpoint customMediaTypesEndpoint() {
+			return new CustomMediaTypesEndpoint();
+		}
+
+	}
+
 	private static final class RequestPredicateMatcher {
 
 		private final String path;