#728 - Fix dependency cycles in WebFlux / WebMVC code

WebHandler is now independent of a particular web stack as the final LinkBuilder creation is externalized through a SAM type that client code now uses to pass a constructor. Refactored the ReactiveLinkBuilder to avoid a dependency on ControllerLinkBuilder (read: the WebMVC stack). With that change, WebHandler is now moved back to the core package.

Refactored LinkBuilderSupport to keep a UriComponentsBuilder instance around instead of UriComponents. It creates a defensive copy of the builder instance on state modifying invocations and returns a new LinkBuilderSupport instance.

Moved SpringMvcAffordanceBuilder to the core package and removed Mvc segment from its name to make obvious it's not tied to SpringMVC. Introduced TemplateVariableAwareLinkBuilderSupport as common base class between ControllerLinkBuilder and ReactiveLinkBuilder. It extracts the TemplateVariable behavior from ControllerLinkBuilder.

Extracted import of web stack specific configuration into dedicated ImportSelector and make use of String based class names to avoid cyclic dependencies between the config packages.

Removed BasicLinkBuilder.

Author: odrotbohm

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

@@ -20,8 +20,6 @@
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
-import java.util.EnumSet;
-import java.util.Set;
 
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Import;
@@ -37,7 +35,7 @@
  * <li>{@link LinkDiscoverer}</li>
  * <li>a Jackson 2 module to correctly marshal the resource model classes into the appropriate representation.
  * </ul>
- * 
+ *
  * @see LinkDiscoverer
  * @see EntityLinks
  * @author Oliver Gierke
@@ -47,35 +45,35 @@
 @Target(ElementType.TYPE)
 @Documented
 @EnableEntityLinks
-@Import({ HypermediaSupportBeanDefinitionRegistrar.class, HateoasConfiguration.class })
+@Import({ HypermediaSupportBeanDefinitionRegistrar.class, HateoasConfiguration.class, WebStackImportSelector.class })
 public @interface EnableHypermediaSupport {
 
 	/**
 	 * The hypermedia type to be supported.
-	 * 
+	 *
 	 * @return
 	 */
 	HypermediaType[] type();
 
 	/**
 	 * Hypermedia representation types supported.
-	 * 
+	 *
 	 * @author Oliver Gierke
 	 * @author Greg Turnquist
 	 */
 	enum HypermediaType {
 
 		/**
 		 * HAL - Hypermedia Application Language.
-		 * 
+		 *
 		 * @see http://stateless.co/hal_specification.html
 		 * @see http://tools.ietf.org/html/draft-kelly-json-hal-05
 		 */
 		HAL,
 
 		/**
 		 * HAL-FORMS - Independent, backward-compatible extension of the HAL designed to add runtime FORM support
-		 * 
+		 *
 		 * @see https://rwcbook.github.io/hal-forms/
 		 */
 		HAL_FORMS,
@@ -93,7 +91,5 @@ enum HypermediaType {
 		 * @see http://uberhypermedia.org/
 		 */
 		UBER;
-
-		private static Set<HypermediaType> HAL_BASED_MEDIATYPES = EnumSet.of(HAL, HAL_FORMS);
 	}
 }

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

@@ -35,19 +35,16 @@
 import org.springframework.hateoas.LinkDiscoverer;
 import org.springframework.hateoas.collectionjson.CollectionJsonLinkDiscoverer;
 import org.springframework.hateoas.config.EnableHypermediaSupport.HypermediaType;
-import org.springframework.hateoas.config.mvc.WebMvcHateoasConfiguration;
-import org.springframework.hateoas.config.reactive.WebFluxHateoasConfiguration;
 import org.springframework.hateoas.hal.HalLinkDiscoverer;
 import org.springframework.hateoas.hal.forms.HalFormsLinkDiscoverer;
-import org.springframework.hateoas.support.WebStack;
 import org.springframework.hateoas.uber.UberLinkDiscoverer;
 import org.springframework.util.ClassUtils;
 
 /**
  * {@link ImportBeanDefinitionRegistrar} implementation to activate hypermedia support based on the configured
  * hypermedia type. Activates {@link EntityLinks} support as well (essentially as if {@link EnableEntityLinks} was
  * activated as well).
- * 
+ *
  * @author Oliver Gierke
  * @author Greg Turnquist
  */
@@ -70,7 +67,7 @@ public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionR
 		 * collection using the application context.
 		 */
 		for (HypermediaType type : types) {
-			
+
 			BeanDefinitionBuilder hypermediaTypeBeanDefinition = genericBeanDefinition(HypermediaType.class, () -> type);
 			registerSourcedBeanDefinition(hypermediaTypeBeanDefinition, metadata, registry);
 		}
@@ -87,30 +84,11 @@ public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionR
 						BeanDefinitionReaderUtils.generateBeanName(linkDiscovererBeanDefinition, registry)), registry);
 			}
 		}
-
-		/*
-		 * Register a Spring MVC-specific HATEOAS configuration.
-		 */
-		if (WebStack.WEBMVC.isAvailable()) {
-			
-			BeanDefinitionBuilder webMvcHateosConfiguration = rootBeanDefinition(WebMvcHateoasConfiguration.class);
-			registerSourcedBeanDefinition(webMvcHateosConfiguration, metadata, registry);
-		}
-
-		/*
-		 * Register a Spring WebFlux-specific HATEOAS configuration.
-		 */
-		if (WebStack.WEBFLUX.isAvailable()) {
-
-			BeanDefinitionBuilder webFluxHateoasConfiguration = rootBeanDefinition(WebFluxHateoasConfiguration.class);
-			registerSourcedBeanDefinition(webFluxHateoasConfiguration, metadata, registry);
-		}
-
 	}
 
 	/**
 	 * Returns a {@link LinkDiscoverer} {@link BeanDefinition} suitable for the given {@link HypermediaType}.
-	 * 
+	 *
 	 * @param type
 	 * @return
 	 */

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

@@ -0,0 +1,51 @@
+/*
+ * 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
+ *
+ *      http://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.config;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.springframework.context.annotation.ImportSelector;
+import org.springframework.core.type.AnnotationMetadata;
+import org.springframework.hateoas.support.WebStack;
+
+/**
+ * {@link ImportSelector} to include web stack specific configuration.
+ *
+ * @author Oliver Drotbohm
+ */
+class WebStackImportSelector implements ImportSelector {
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.context.annotation.ImportSelector#selectImports(org.springframework.core.type.AnnotationMetadata)
+	 */
+	@Override
+	public String[] selectImports(AnnotationMetadata importingClassMetadata) {
+
+		List<String> imports = new ArrayList<>();
+
+		if (WebStack.WEBMVC.isAvailable()) {
+			imports.add("org.springframework.hateoas.config.mvc.WebMvcHateoasConfiguration");
+		}
+
+		if (WebStack.WEBFLUX.isAvailable()) {
+			imports.add("org.springframework.hateoas.config.reactive.WebFluxHateoasConfiguration");
+		}
+
+		return imports.toArray(new String[imports.size()]);
+	}
+}

src/main/java/org/springframework/hateoas/config/mvc/HypermediaWebMvcConfigurer.java

@@ -22,6 +22,7 @@
 
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.List;
 
 import org.springframework.beans.BeansException;
@@ -101,10 +102,10 @@ public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
 
 		if (this.hypermediaTypes.contains(HypermediaType.HAL_FORMS)) {
 
-			converters.add(0,
-					new TypeConstrainedMappingJackson2HttpMessageConverter(ResourceSupport.class,
-							Collections.singletonList(HAL_FORMS_JSON), createHalFormsObjectMapper(this.mapper, this.curieProvider,
-									this.relProvider, linkRelationMessageSource, this.halFormsConfiguration)));
+				converters.add(0, new TypeConstrainedMappingJackson2HttpMessageConverter(
+					ResourceSupport.class, Collections.singletonList(HAL_FORMS_JSON),
+					createHalFormsObjectMapper(this.mapper, this.curieProvider, this.relProvider, linkRelationMessageSource,
+						this.halFormsConfiguration)));
 		}
 
 		if (this.hypermediaTypes.contains(HypermediaType.COLLECTION_JSON)) {
@@ -115,8 +116,8 @@ public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
 
 		if (this.hypermediaTypes.contains(HypermediaType.UBER)) {
 
-			converters.add(0, new TypeConstrainedMappingJackson2HttpMessageConverter(ResourceSupport.class,
-					Collections.singletonList(UBER_JSON), createUberObjectMapper(this.mapper)));
+			converters.add(0, new TypeConstrainedMappingJackson2HttpMessageConverter(
+				ResourceSupport.class, Collections.singletonList(UBER_JSON), createUberObjectMapper(this.mapper)));
 		}
 	}
 }

src/main/java/org/springframework/hateoas/config/mvc/WebMvcHateoasConfiguration.java

@@ -30,27 +30,21 @@
 
 /**
  * Spring MVC HATEOAS Configuration
- * 
+ *
  * @author Greg Turnquist
  */
 @Configuration
 public class WebMvcHateoasConfiguration {
 
 	@Bean
 	HypermediaWebMvcConfigurer hypermediaWebMvcConfigurer(ObjectProvider<ObjectMapper> mapper,
-														  DelegatingRelProvider relProvider,
-														  ObjectProvider<CurieProvider> curieProvider,
-														  ObjectProvider<HalConfiguration> halConfiguration,
-														  ObjectProvider<HalFormsConfiguration> halFormsConfiguration,
-														  Collection<HypermediaType> hypermediaTypes) {
-		
-		return new HypermediaWebMvcConfigurer(
-			mapper.getIfAvailable(ObjectMapper::new),
-			relProvider,
-			curieProvider.getIfAvailable(),
-			halConfiguration.getIfAvailable(HalConfiguration::new),
-			halFormsConfiguration.getIfAvailable(HalFormsConfiguration::new),
-			hypermediaTypes);
+			DelegatingRelProvider relProvider, ObjectProvider<CurieProvider> curieProvider,
+			ObjectProvider<HalConfiguration> halConfiguration, ObjectProvider<HalFormsConfiguration> halFormsConfiguration,
+			Collection<HypermediaType> hypermediaTypes) {
+
+		return new HypermediaWebMvcConfigurer(mapper.getIfAvailable(ObjectMapper::new), relProvider,
+				curieProvider.getIfAvailable(), halConfiguration.getIfAvailable(HalConfiguration::new),
+				halFormsConfiguration.getIfAvailable(HalFormsConfiguration::new), hypermediaTypes);
 	}
 
 	@Bean

src/main/java/org/springframework/hateoas/config/reactive/WebFluxHateoasConfiguration.java

@@ -31,53 +31,42 @@
 
 /**
  * Spring WebFlux HATEOAS configuration.
- * 
+ *
  * @author Greg Turnquist
  * @since 1.0
  */
 @Configuration
 public class WebFluxHateoasConfiguration {
 
 	@Bean
-	WebClientConfigurer webClientConfigurer(ObjectProvider<ObjectMapper> mapper,
-											DelegatingRelProvider relProvider,
-											ObjectProvider<CurieProvider> curieProvider,
-											ObjectProvider<HalConfiguration> halConfiguration,
-											ObjectProvider<HalFormsConfiguration> halFormsConfiguration,
-											Collection<HypermediaType> hypermediaTypes) {
-		
-		return new WebClientConfigurer(
-			mapper.getIfAvailable(ObjectMapper::new),
-			relProvider,
-			curieProvider.getIfAvailable(),
-			halConfiguration.getIfAvailable(HalConfiguration::new),
-			halFormsConfiguration.getIfAvailable(HalFormsConfiguration::new),
-			hypermediaTypes);
+	WebClientConfigurer webClientConfigurer(ObjectProvider<ObjectMapper> mapper, DelegatingRelProvider relProvider,
+			ObjectProvider<CurieProvider> curieProvider, ObjectProvider<HalConfiguration> halConfiguration,
+			ObjectProvider<HalFormsConfiguration> halFormsConfiguration, Collection<HypermediaType> hypermediaTypes) {
+
+		return new WebClientConfigurer(mapper.getIfAvailable(ObjectMapper::new), relProvider,
+				curieProvider.getIfAvailable(), halConfiguration.getIfAvailable(HalConfiguration::new),
+				halFormsConfiguration.getIfAvailable(HalFormsConfiguration::new), hypermediaTypes);
 	}
 
 	@Bean
 	HypermediaWebClientBeanPostProcessor webClientBeanPostProcessor(WebClientConfigurer configurer) {
 		return new HypermediaWebClientBeanPostProcessor(configurer);
 	}
-	
+
 	@Bean
 	HypermediaWebFluxConfigurer hypermediaWebFluxConfigurer(ObjectProvider<ObjectMapper> mapper,
-															DelegatingRelProvider relProvider,
-															ObjectProvider<CurieProvider> curieProvider,
-															ObjectProvider<HalConfiguration> halConfiguration,
-															ObjectProvider<HalFormsConfiguration> halFormsConfiguration,
-															Collection<HypermediaType> hypermediaTypes) {
+			DelegatingRelProvider relProvider, ObjectProvider<CurieProvider> curieProvider,
+			ObjectProvider<HalConfiguration> halConfiguration, ObjectProvider<HalFormsConfiguration> halFormsConfiguration,
+			Collection<HypermediaType> hypermediaTypes) {
 
-		return new HypermediaWebFluxConfigurer(
-			mapper.getIfAvailable(ObjectMapper::new),
-			relProvider,
-			curieProvider.getIfAvailable(),
-			halConfiguration.getIfAvailable(HalConfiguration::new),
-			halFormsConfiguration.getIfAvailable(HalFormsConfiguration::new), hypermediaTypes);
+		return new HypermediaWebFluxConfigurer(mapper.getIfAvailable(ObjectMapper::new), relProvider,
+				curieProvider.getIfAvailable(), halConfiguration.getIfAvailable(HalConfiguration::new),
+				halFormsConfiguration.getIfAvailable(HalFormsConfiguration::new), hypermediaTypes);
 	}
 
 	/**
-	 * TODO: Replace with Spring Framework filter when https://github.com/spring-projects/spring-framework/issues/21746 is completed.
+	 * TODO: Replace with Spring Framework filter when https://github.com/spring-projects/spring-framework/issues/21746 is
+	 * completed.
 	 */
 	@Bean
 	HypermediaWebFilter hypermediaWebFilter() {

src/main/java/org/springframework/hateoas/core/DummyInvocationUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2019 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.