#572 - Create SimpleResourceAssembler for Resource<T>.

Implement a ResourceAssembler based solely on a domain type, returning Resource<T> for the `toResource(obj)` method.

Related issues: #416

Author: gregturn

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -19,15 +19,15 @@
 import java.util.List;
 
 /**
- * Interface for components that convert a domain type into an {@link ResourceSupport}.
+ * Interface for components that convert a domain type into a {@link ResourceSupport}.
  * 
  * @author Oliver Gierke
  * @author Greg Turnquist
  */
 public interface ResourceAssembler<T, D extends ResourceSupport> {
 
 	/**
-	 * Converts the given entity into an {@link ResourceSupport}.
+	 * Converts the given entity into a {@code D}, which extends {@link ResourceSupport}.
 	 * 
 	 * @param entity
 	 * @return
@@ -38,10 +38,10 @@ public interface ResourceAssembler<T, D extends ResourceSupport> {
 	 * Converts an {@link Iterable} or {@code T}s into an {@link Iterable} of {@link ResourceSupport} and wraps
 	 * them in a {@link Resources} instance.
 	 * 
-	 * @param entities
-	 * @return
+	 * @param entities must not be {@literal null}.
+	 * @return {@link Resources} containing {@code D}.
 	 */
-	default Resources<D> toResources(List<T> entities) {
+	default Resources<D> toResources(Iterable<? extends T> entities) {
 
 		List<D> resources = new ArrayList<>();
 		for (T entity : entities) {

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

@@ -0,0 +1,84 @@
+/*
+ * Copyright 2018 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 java.util.ArrayList;
+import java.util.List;
+
+import org.springframework.util.Assert;
+
+/**
+ * A {@link ResourceAssembler} based purely on the domain type, using {@code Resource<T>} as the enclosing
+ * "resource" type.
+ *
+ * @author Greg Turnquist
+ * @since 1.0
+ */
+public interface SimpleResourceAssembler<T> extends ResourceAssembler<T, Resource<T>> {
+
+	/**
+	 * Converts the given entity into a {@link Resource}.
+	 *
+	 * @param entity
+	 * @return
+	 */
+	default Resource<T> toResource(T entity) {
+		
+		Resource<T> resource = new Resource<>(entity);
+		addLinks(resource);
+		return resource;
+	}
+
+	/**
+	 * Define links to add to every individual {@link Resource}.
+	 *
+	 * @param resource
+	 */
+	default void addLinks(Resource<T> resource) {
+		// By default, add no links.
+	}
+
+	/**
+	 * Converts all given entities into resources and wraps the collection as a resource as well.
+	 *
+	 * @see #toResource(Object)
+	 * @param entities must not be {@literal null}.
+	 * @return {@link Resources} containing {@link Resource} of {@code T}.
+	 */
+	@Override
+	default Resources<Resource<T>> toResources(Iterable<? extends T> entities) {
+
+		Assert.notNull(entities, "entities must not be null!");
+		List<Resource<T>> resourceList = new ArrayList<>();
+
+		for (T entity : entities) {
+			resourceList.add(toResource(entity));
+		}
+
+		Resources<Resource<T>> resources = new Resources<>(resourceList);
+		addLinks(resources);
+		return resources;
+	}
+
+	/**
+	 * Define links to add to the {@link Resources} collection.
+	 *
+	 * @param resources
+	 */
+	default void addLinks(Resources<Resource<T>> resources) {
+		// By default, add no links.
+	}
+}

src/main/java/org/springframework/hateoas/mvc/ResourceAssemblerSupport.java

@@ -54,7 +54,7 @@ public ResourceAssemblerSupport(Class<?> controllerClass, Class<D> resourceType)
 	}
 
 	@Override
-	public Resources<D> toResources(List<T> entities) {
+	public Resources<D> toResources(Iterable<? extends T> entities) {
 		return this.map(entities).toResources();
 	}
 

src/test/java/org/springframework/hateoas/SimpleResourceAssemblerTest.java

@@ -0,0 +1,108 @@
+/*
+ * Copyright 2018 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 static org.assertj.core.api.Assertions.*;
+
+import lombok.Data;
+
+import java.util.Collections;
+
+import org.junit.Test;
+
+/**
+ * @author Greg Turnquist
+ */
+public class SimpleResourceAssemblerTest {
+
+	/**
+	 * @see #572
+	 */
+	@Test
+	public void convertingToResourceShouldWork() {
+
+		TestResourceAssembler assembler = new TestResourceAssembler();
+		Resource<Employee> resource = assembler.toResource(new Employee("Frodo"));
+
+		assertThat(resource.getContent().getName()).isEqualTo("Frodo");
+		assertThat(resource.getLinks()).isEmpty();
+	}
+
+	/**
+	 * @see #572
+	 */
+	@Test
+	public void convertingToResourcesShouldWork() {
+
+		TestResourceAssembler assembler = new TestResourceAssembler();
+		Resources<Resource<Employee>> resources = assembler.toResources(Collections.singletonList(new Employee("Frodo")));
+
+		assertThat(resources.getContent()).hasSize(1);
+		assertThat(resources.getContent()).containsExactly(new Resource<>(new Employee("Frodo")));
+		assertThat(resources.getLinks()).isEmpty();
+
+		assertThat(resources.getContent().iterator().next()).isEqualTo(new Resource<>(new Employee("Frodo")));
+	}
+
+	/**
+	 * @see #572
+	 */
+	@Test
+	public void convertingToResourceWithCustomLinksShouldWork() {
+
+		ResourceAssemblerWithCustomLink assembler = new ResourceAssemblerWithCustomLink();
+		Resource<Employee> resource = assembler.toResource(new Employee("Frodo"));
+
+		assertThat(resource.getContent().getName()).isEqualTo("Frodo");
+		assertThat(resource.getLinks()).hasSize(1);
+		assertThat(resource.getLinks()).containsExactly(new Link("/employees").withRel("employees"));
+	}
+
+	/**
+	 * @see #572
+	 */
+	@Test
+	public void convertingToResourcesWithCustomLinksShouldWork() {
+
+		ResourceAssemblerWithCustomLink assembler = new ResourceAssemblerWithCustomLink();
+		Resources<Resource<Employee>> resources = assembler.toResources(Collections.singletonList(new Employee("Frodo")));
+
+		assertThat(resources.getContent()).hasSize(1);
+		assertThat(resources.getContent())
+			.containsExactly(new Resource<>(new Employee("Frodo"), new Link("/employees").withRel("employees")));
+		assertThat(resources.getLinks()).isEmpty();
+
+		assertThat(resources.getContent().iterator().next())
+			.isEqualTo(new Resource<>(new Employee("Frodo"), new Link("/employees").withRel("employees")));
+	}
+
+
+	class TestResourceAssembler implements SimpleResourceAssembler<Employee> {}
+
+	class ResourceAssemblerWithCustomLink implements SimpleResourceAssembler<Employee> {
+
+		@Override
+		public void addLinks(Resource<Employee> resource) {
+			resource.add(new Link("/employees").withRel("employees"));
+		}
+	}
+
+	@Data
+	class Employee {
+		private final String name;
+	}
+}

src/test/java/org/springframework/hateoas/mvc/IdentifiableResourceAssemblerSupportUnitTest.java

@@ -24,6 +24,7 @@
 
 import org.junit.Before;
 import org.junit.Test;
+
 import org.springframework.hateoas.Identifiable;
 import org.springframework.hateoas.Link;
 import org.springframework.hateoas.LinkBuilder;