Enhancements of Resource abstraction.

Introduced Resource and Resources value objects. The former captures single entity instances but adds links to it. The latter does the same for a collection of entities. Added SPI interfaces ResourcePostProcessor and ResourcesPostProcessor to allow manipulating Resource and Resources instances.

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

@@ -0,0 +1,98 @@
+/*
+ * 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 java.util.ArrayList;
+import java.util.Collection;
+import java.util.Iterator;
+
+import javax.xml.bind.annotation.XmlAnyElement;
+import javax.xml.bind.annotation.XmlElementWrapper;
+import javax.xml.bind.annotation.XmlRootElement;
+
+import org.codehaus.jackson.annotate.JsonProperty;
+import org.springframework.util.Assert;
+
+/**
+ * General helper to easily create a wrapper for a collection of entities.
+ * 
+ * @author Oliver Gierke
+ */
+@XmlRootElement(name = "entities")
+public class Resources<T extends Resource<?>> extends ResourceSupport implements Iterable<T> {
+
+	@XmlAnyElement
+	@XmlElementWrapper
+	@JsonProperty("content")
+	private final Collection<T> content;
+
+	/**
+	 * Creates an empty {@link Resources} instance.
+	 */
+	protected Resources() {
+		this(new ArrayList<T>());
+	}
+
+	/**
+	 * Creates a {@link Resources} instance with the given content.
+	 * 
+	 * @param content must not be {@literal null}.
+	 */
+	public Resources(Collection<T> content) {
+
+		Assert.notNull(content);
+
+		this.content = new ArrayList<T>();
+		this.content.addAll(content);
+	}
+
+	/**
+	 * Creates a new {@link Resources} instance by wrapping the given domain class instances into a {@link Resource}.
+	 * 
+	 * @param content must not be {@literal null}.
+	 * @return
+	 */
+	@SuppressWarnings("unchecked")
+	public static <T extends Resource<S>, S> Resources<T> fromEntities(Collection<S> content) {
+
+		Assert.notNull(content);
+		ArrayList<T> resources = new ArrayList<T>();
+
+		for (S element : content) {
+			resources.add((T) new Resource<S>(element));
+		}
+
+		return new Resources<T>(resources);
+	}
+
+	/**
+	 * Returns the underlying {@link Resource}s.
+	 * 
+	 * @return the content will never be {@literal null}.
+	 */
+	public Collection<T> getContent() {
+		return content;
+	}
+
+	/* 
+	 * (non-Javadoc)
+	 * @see java.lang.Iterable#iterator()
+	 */
+	@Override
+	public Iterator<T> iterator() {
+		return content.iterator();
+	}
+}