Introduced EntityLinks abstraction.

EntityLinks allow accessing LinkBuilders or even Link instance based on components exposing REST resources for a particular domain type. The core implementation is ControllerEntityLinks that assumes a particular URI structure so that it can derive the URIs to be asked for per domain type. The domain type managed will be inspected from the @ExposesResourceFor annotation on a controller class. We provide a factory bean to allow configuring instances of ControllerEntityLinks based on a mapping annotation and LinkBuilderFactory.

Added infrastructure to activate automatic discovery of EntityLinks implementations through @EnableEntityLinks. This will automatically register ControllerEntityLinks instances for Spring MVC controllers annotated with @ExposesResourceFor as well as JAX-RS resources if JAX-RS is on the classpath. The mechanism essentially registers a DelegatingEntityLinks instance leveraging the Spring Plugin PluginRegistry mechanism to delegate to the actual EntityLinks instance actually registered for the entity type. It will become the primary EntityLinks bean in the ApplicationContext so that they can be autowired into client components safely.

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

@@ -0,0 +1,91 @@
+/*
+ * Copyright 2012 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;
+
+import org.springframework.plugin.core.Plugin;
+
+/**
+ * Accessor to links pointing to controllers backing an entity type.
+ * 
+ * @author Oliver Gierke
+ */
+public interface EntityLinks extends Plugin<Class<?>> {
+
+	/**
+	 * Returns a {@link LinkBuilder} able to create links to the controller managing the given entity type. Expects a
+	 * controller being mapped to a fully expanded URI template (i.e. not path variables being used).
+	 * 
+	 * @param type the entity type to point to, must not be {@literal null}.
+	 * @return the {@link LinkBuilder} pointing to the collection resource. Will never be {@literal null}.
+	 */
+	LinkBuilder linkFor(Class<?> type);
+
+	/**
+	 * Returns a {@link LinkBuilder} able to create links to the controller managing the given entity type, unfolding the
+	 * given parameters into the URI template the backing controller is mapped to.
+	 * 
+	 * @param type the entity type to point to, must not be {@literal null}.
+	 * @return the {@link LinkBuilder} pointing to the collection resource. Will never be {@literal null}.
+	 */
+	LinkBuilder linkFor(Class<?> type, Object... parameters);
+
+	/**
+	 * Returns a {@link LinkBuilder} able to create links to the controller managing the given entity type and id.
+	 * Implementations will know about the URI structure being used to expose single-resource URIs.
+	 * 
+	 * @param type the entity type to point to, must not be {@literal null}.
+	 * @param id the id of the object of the handed type, {@link Identifiable}s will be unwrapped.
+	 * @return
+	 */
+	LinkBuilder linkForSingleResource(Class<?> type, Object id);
+
+	/**
+	 * Returns a {@link LinkBuilder} able to create links to the controller managing the given entity.
+	 * 
+	 * @see #linkForSingleResource(Class, Object)
+	 * @param entity the entity type to point to, must not be {@literal null}.
+	 * @return
+	 */
+	LinkBuilder linkForSingleResource(Identifiable<?> entity);
+
+	/**
+	 * Creates a {@link Link} pointing to the collection resource of the given type. The relation type of the link will be
+	 * determined by the implementation class and should be defaulted to {@link Link#REL_SELF}.
+	 * 
+	 * @param type the entity type to point to, must not be {@literal null}.
+	 * @return
+	 */
+	Link linkToCollectionResource(Class<?> type);
+
+	/**
+	 * Creates a {@link Link} pointing to single resource backing the given entity type and id. The relation type of the
+	 * link will be determined by the implementation class and should be defaulted to {@link Link#REL_SELF}.
+	 * 
+	 * @param type the entity type to point to, must not be {@literal null}.
+	 * @param id
+	 * @return
+	 */
+	Link linkToSingleResource(Class<?> type, Object id);
+
+	/**
+	 * Creates a {@link Link} pointing to single resource backing the given entity. The relation type of the link will be
+	 * determined by the implementation class and should be defaulted to {@link Link#REL_SELF}.
+	 * 
+	 * @param entity the entity type to point to, must not be {@literal null}.
+	 * @return
+	 */
+	Link linkToSingleResource(Identifiable<?> entity);
+}