IdentifiableResourceAssemblerSupport.java

/*
 * Copyright 2012-2013 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.mvc;

import static org.springframework.hateoas.mvc.ControllerLinkBuilder.*;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import org.springframework.hateoas.Identifiable;
import org.springframework.hateoas.ResourceAssembler;
import org.springframework.hateoas.ResourceSupport;
import org.springframework.util.Assert;

/**
 * Base class to implement {@link ResourceAssembler}s. Will automate {@link ResourceSupport} instance creation and make
 * sure a self-link is always added.
 * 
 * @author Oliver Gierke
 */
public abstract class IdentifiableResourceAssemblerSupport<T extends Identifiable<?>, D extends ResourceSupport>
		extends ResourceAssemblerSupport<T, D> {

	private final Class<?> controllerClass;

	/**
	 * Creates a new {@link ResourceAssemblerSupport} using the given controller class and resource type.
	 * 
	 * @param controllerClass must not be {@literal null}.
	 * @param resourceType must not be {@literal null}.
	 */
	public IdentifiableResourceAssemblerSupport(Class<?> controllerClass, Class<D> resourceType) {

		super(controllerClass, resourceType);
		this.controllerClass = controllerClass;
	}

	/**
	 * Creates a new resource and adds a self link to it consisting using the {@link Identifiable}'s id.
	 * 
	 * @param entity must not be {@literal null}.
	 * @return
	 */
	protected D createResource(T entity) {
		return createResource(entity, new Object[0]);
	}

	protected D createResource(T entity, Object... parameters) {
		return createResourceWithId(entity.getId(), entity, parameters);
	}

	@Override
	protected D createResourceWithId(Object id, T entity, Object... parameters) {

		Assert.notNull(entity, "Entity must not be null!");
		Assert.notNull(id, "Id must not be null!");

		D instance = instantiateResource(entity);
		instance.add(linkTo(controllerClass, unwrapIdentifyables(parameters)).slash(id).withSelfRel());
		return instance;
	}

	/**
	 * Extracts the ids of the given values in case they're {@link Identifiable}s. Returns all other objects as they are.
	 * 
	 * @param values must not be {@literal null}.
	 * @return
	 */
	private Object[] unwrapIdentifyables(Object[] values) {

		List<Object> result = new ArrayList<Object>(values.length);

		for (Object element : Arrays.asList(values)) {
			result.add(element instanceof Identifiable ? ((Identifiable<?>) element).getId() : element);
		}

		return result.toArray();
	}
}