#1060 - When EnableHypermediaSupport has an empty list, enable all.

Default it to being empty. Existing code, `@EnableHypermediaSupport(types = HAL)` will still operate as expected. But simply using the annotation with no arguments will activate ALL types.

Related issues: #1015.
Related pull request: #1065.

src/main/java/org/springframework/hateoas/config/EnableHypermediaSupport.java

@@ -44,11 +44,12 @@
 public @interface EnableHypermediaSupport {
 
 	/**
-	 * The hypermedia type to be supported.
+	 * The hypermedia type to be supported. By default, it is empty, thus activating all available
+	 * {@link MediaTypeConfigurationProvider}s.
 	 *
 	 * @return
 	 */
-	HypermediaType[] type();
+	HypermediaType[] type() default {};
 
 	/**
 	 * Configures which {@link WebStack}s we're supposed to enable support for. By default we're activating it for all

src/main/java/org/springframework/hateoas/config/HypermediaConfigurationImportSelector.java

@@ -62,7 +62,7 @@ public String[] selectImports(AnnotationMetadata metadata) {
 
 		Map<String, Object> attributes = metadata.getAnnotationAttributes(EnableHypermediaSupport.class.getName());
 
-		List<MediaType> types = attributes == null //
+		List<MediaType> mediaTypes = attributes == null //
 				? Collections.emptyList() //
 				: Arrays.stream((HypermediaType[]) attributes.get("type")) //
 						.flatMap(it -> it.getMediaTypes().stream()) //
@@ -71,9 +71,9 @@ public String[] selectImports(AnnotationMetadata metadata) {
 		List<MediaTypeConfigurationProvider> configurationProviders = SpringFactoriesLoader.loadFactories(
 				MediaTypeConfigurationProvider.class, HypermediaConfigurationImportSelector.class.getClassLoader());
 
-		// Filter the ones supporting the given media types
+		// Filter the ones supporting the given media types, or let them all through if none declared.
 		Stream<String> imports = configurationProviders.stream() //
-				.filter(it -> it.supportsAny(types)) //
+				.filter(it -> mediaTypes.isEmpty() || it.supportsAny(mediaTypes)) //
 				.map(MediaTypeConfigurationProvider::getConfiguration) //
 				.map(Class::getName);
 

src/test/java/org/springframework/hateoas/config/HypermediaConfigurationImportSelectorUnitTest.java

@@ -106,16 +106,32 @@ void includesWebTestHateoasConfigurationIfWebTestClientIsOnTheClasspath() {
 	@Test // #1252
 	void doesNotIncludeWebTestHateoasConfigurationIfWebTestClientIsNotOnTheClasspath() {
 
-		HidingClassLoader delegate = HidingClassLoader.hide(WebTestClientConfigurer.class);
-		ShadowingClassLoader loader = new ShadowingClassLoader(delegate);
-		loader.excludePackage("org.springframework");
+        HidingClassLoader delegate = HidingClassLoader.hide(WebTestClientConfigurer.class);
+        ShadowingClassLoader loader = new ShadowingClassLoader(delegate);
+        loader.excludePackage("org.springframework");
 
-		withContext(HalConfig.class, context -> {
+        withContext(HalConfig.class, context -> {
+
+            assertThatExceptionOfType(NoSuchBeanDefinitionException.class)
+                .isThrownBy(() -> context.getBean(WebTestHateoasConfiguration.class));
+
+        }, loader);
+    }
 
-			assertThatExceptionOfType(NoSuchBeanDefinitionException.class)
-					.isThrownBy(() -> context.getBean(WebTestHateoasConfiguration.class));
+	@Test // #1060
+	void testEmptyHypermediaTypes() {
+
+		withContext(NoConfig.class, context -> {
+
+			Map<String, LinkDiscoverer> linkDiscoverers = context.getBeansOfType(LinkDiscoverer.class);
 
-		}, loader);
+			assertThat(linkDiscoverers.values()).extracting("class") //
+				.containsExactlyInAnyOrder( //
+					HalLinkDiscoverer.class, //
+					HalFormsLinkDiscoverer.class, //
+					UberLinkDiscoverer.class, //
+					CollectionJsonLinkDiscoverer.class);
+		});
 	}
 
 	@EnableHypermediaSupport(type = HAL)
@@ -137,4 +153,9 @@ static class HalAndHalFormsConfig {
 	static class AllConfig {
 
 	}
+
+	@EnableHypermediaSupport(type = { })
+	static class NoConfig {
+
+	}
 }

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

@@ -0,0 +1,38 @@
+/*
+ * 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.support;
+
+import java.util.Collection;
+
+import org.springframework.hateoas.config.HypermediaMappingInformation;
+import org.springframework.hateoas.config.MediaTypeConfigurationProvider;
+import org.springframework.http.MediaType;
+
+/**
+ * @author Greg Turnquist
+ */
+public class CustomHypermediaConfigurationProvider implements MediaTypeConfigurationProvider {
+
+	@Override
+	public Class<? extends HypermediaMappingInformation> getConfiguration() {
+		return CustomHypermediaType.class;
+	}
+
+	@Override
+	public boolean supportsAny(Collection<MediaType> mediaTypes) {
+		return mediaTypes.stream().anyMatch(mediaType -> mediaType.isCompatibleWith(CustomHypermediaType.FRODO_MEDIATYPE));
+	}
+}

src/test/resources/META-INF/spring.factories

@@ -0,0 +1,2 @@
+org.springframework.hateoas.config.MediaTypeConfigurationProvider=\
+ org.springframework.hateoas.support.CustomHypermediaConfigurationProvider