Allow operations to produce different output

Update the actuator @Enpoint` infrastructure code so that operations
may inject enums that indicate the type of output to produce. A new
`Producible` interface can be implemented by any enum that indicates
the mime-type that an enum value produces.

The new `OperationArgumentResolver` provides a general strategy for
resolving operation arguments with `ProducibleOperationArgumentResolver`
providing support for `Producible` enums. Existing injection support has
been refactored to use the new resolver.

See gh-25738

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/InvocationContextTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -39,11 +39,24 @@ class InvocationContextTests {
 	private final Map<String, Object> arguments = Collections.singletonMap("test", "value");
 
 	@Test
+	@SuppressWarnings("deprecation")
 	void createWhenApiVersionIsNullUsesLatestVersion() {
 		InvocationContext context = new InvocationContext(null, this.securityContext, this.arguments);
 		assertThat(context.getApiVersion()).isEqualTo(ApiVersion.LATEST);
 	}
 
+	@Test
+	void whenCreatedWithoutApiVersionThenGetApiVersionReturnsLatestVersion() {
+		InvocationContext context = new InvocationContext(this.securityContext, this.arguments);
+		assertThat(context.getApiVersion()).isEqualTo(ApiVersion.LATEST);
+	}
+
+	@Test
+	void whenCreatedWithoutApiVersionThenResolveApiVersionReturnsLatestVersion() {
+		InvocationContext context = new InvocationContext(this.securityContext, this.arguments);
+		assertThat(context.resolveArgument(ApiVersion.class)).isEqualTo(ApiVersion.LATEST);
+	}
+
 	@Test
 	void createWhenSecurityContextIsNullThrowsException() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new InvocationContext(null, this.arguments))
@@ -57,17 +70,25 @@ class InvocationContextTests {
 	}
 
 	@Test
+	@SuppressWarnings("deprecation")
 	void getApiVersionReturnsApiVersion() {
 		InvocationContext context = new InvocationContext(ApiVersion.V2, this.securityContext, this.arguments);
 		assertThat(context.getApiVersion()).isEqualTo(ApiVersion.V2);
 	}
 
 	@Test
+	@SuppressWarnings("deprecation")
 	void getSecurityContextReturnsSecurityContext() {
 		InvocationContext context = new InvocationContext(this.securityContext, this.arguments);
 		assertThat(context.getSecurityContext()).isEqualTo(this.securityContext);
 	}
 
+	@Test
+	void resolveSecurityContextReturnsSecurityContext() {
+		InvocationContext context = new InvocationContext(this.securityContext, this.arguments);
+		assertThat(context.resolveArgument(SecurityContext.class)).isEqualTo(this.securityContext);
+	}
+
 	@Test
 	void getArgumentsReturnsArguments() {
 		InvocationContext context = new InvocationContext(this.securityContext, this.arguments);

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/http/ApiVersionTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -82,6 +82,12 @@ class ApiVersionTests {
 		assertThat(version).isEqualTo(ApiVersion.V3);
 	}
 
+	@Test
+	void fromHttpHeadersWhenAcceptsEverythingReturnsLatest() {
+		ApiVersion version = ApiVersion.fromHttpHeaders(acceptHeader("*/*"));
+		assertThat(version).isEqualTo(ApiVersion.V3);
+	}
+
 	private Map<String, List<String>> acceptHeader(String... types) {
 		List<String> value = Arrays.asList(types);
 		return value.isEmpty() ? Collections.emptyMap() : Collections.singletonMap("Accept", value);

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/http/ProducibleOperationArgumentResolverTests.java

@@ -0,0 +1,79 @@
+/*
+ * Copyright 2012-2021 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.boot.actuate.endpoint.http;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Test for {@link ProducibleOperationArgumentResolver}.
+ *
+ * @author Andy Wilkinson
+ */
+class ProducibleOperationArgumentResolverTests {
+
+	@Test
+	void whenAcceptHeaderIsEmptyThenHighestOrdinalIsReturned() {
+		assertThat(resolve(acceptHeader())).isEqualTo(ApiVersion.V3);
+	}
+
+	@Test
+	void whenEverythingIsAcceptableThenHighestOrdinalIsReturned() {
+		assertThat(resolve(acceptHeader("*/*"))).isEqualTo(ApiVersion.V3);
+	}
+
+	@Test
+	void whenNothingIsAcceptableThenNullIsReturned() {
+		assertThat(resolve(acceptHeader("image/png"))).isEqualTo(null);
+	}
+
+	@Test
+	void whenSingleValueIsAcceptableThenMatchingEnumValueIsReturned() {
+		assertThat(new ProducibleOperationArgumentResolver(acceptHeader(ActuatorMediaType.V2_JSON))
+				.resolve(ApiVersion.class)).isEqualTo(ApiVersion.V2);
+		assertThat(new ProducibleOperationArgumentResolver(acceptHeader(ActuatorMediaType.V3_JSON))
+				.resolve(ApiVersion.class)).isEqualTo(ApiVersion.V3);
+	}
+
+	@Test
+	void whenMultipleValuesAreAcceptableThenHighestOrdinalIsReturned() {
+		assertThat(resolve(acceptHeader(ActuatorMediaType.V2_JSON, ActuatorMediaType.V3_JSON)))
+				.isEqualTo(ApiVersion.V3);
+	}
+
+	@Test
+	void whenMultipleValuesAreAcceptableAsSingleHeaderThenHighestOrdinalIsReturned() {
+		assertThat(resolve(acceptHeader(ActuatorMediaType.V2_JSON + "," + ActuatorMediaType.V3_JSON)))
+				.isEqualTo(ApiVersion.V3);
+	}
+
+	private Map<String, List<String>> acceptHeader(String... types) {
+		List<String> value = Arrays.asList(types);
+		return value.isEmpty() ? Collections.emptyMap() : Collections.singletonMap("Accept", value);
+	}
+
+	private ApiVersion resolve(Map<String, List<String>> httpHeaders) {
+		return new ProducibleOperationArgumentResolver(httpHeaders).resolve(ApiVersion.class);
+	}
+
+}

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/invoker/cache/CachingOperationInvokerTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -18,6 +18,7 @@ package org.springframework.boot.actuate.endpoint.invoker.cache;
 
 import java.security.Principal;
 import java.time.Duration;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
@@ -28,6 +29,7 @@ import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
 import org.springframework.boot.actuate.endpoint.InvocationContext;
+import org.springframework.boot.actuate.endpoint.OperationArgumentResolver;
 import org.springframework.boot.actuate.endpoint.SecurityContext;
 import org.springframework.boot.actuate.endpoint.http.ApiVersion;
 import org.springframework.boot.actuate.endpoint.invoke.MissingParametersException;
@@ -200,10 +202,10 @@ class CachingOperationInvokerTests {
 		OperationInvoker target = mock(OperationInvoker.class);
 		Object expectedV2 = new Object();
 		Object expectedV3 = new Object();
-		InvocationContext contextV2 = new InvocationContext(ApiVersion.V2, mock(SecurityContext.class),
-				Collections.emptyMap());
-		InvocationContext contextV3 = new InvocationContext(ApiVersion.V3, mock(SecurityContext.class),
-				Collections.emptyMap());
+		InvocationContext contextV2 = new InvocationContext(mock(SecurityContext.class), Collections.emptyMap(),
+				Arrays.asList(new ApiVersionArgumentResolver(ApiVersion.V2)));
+		InvocationContext contextV3 = new InvocationContext(mock(SecurityContext.class), Collections.emptyMap(),
+				Arrays.asList(new ApiVersionArgumentResolver(ApiVersion.V3)));
 		given(target.invoke(contextV2)).willReturn(expectedV2);
 		given(target.invoke(contextV3)).willReturn(expectedV3);
 		CachingOperationInvoker invoker = new CachingOperationInvoker(target, CACHE_TTL);
@@ -240,4 +242,25 @@ class CachingOperationInvokerTests {
 
 	}
 
+	private static final class ApiVersionArgumentResolver implements OperationArgumentResolver {
+
+		private final ApiVersion apiVersion;
+
+		private ApiVersionArgumentResolver(ApiVersion apiVersion) {
+			this.apiVersion = apiVersion;
+		}
+
+		@SuppressWarnings("unchecked")
+		@Override
+		public <T> T resolve(Class<T> type) {
+			return (T) this.apiVersion;
+		}
+
+		@Override
+		public boolean canResolve(Class<?> type) {
+			return ApiVersion.class.equals(type);
+		}
+
+	}
+
 }