#85 - Added HeaderLinksResponseEntity.

The HeaderLinksResponseEntity wraps any HttpEntity containing a ResourceSupport and will transform it to contain the Links the ResourceSupport instance held in the first place in the entities headers now.

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

@@ -98,6 +98,13 @@ public class ResourceSupport implements Identifiable<Link> {
 		return Collections.unmodifiableList(links);
 	}
 
+	/**
+	 * Removes all {@link Link}s added to the resource so far.
+	 */
+	public void removeLinks() {
+		this.links.clear();
+	}
+
 	/**
 	 * Returns the link with the given rel.
 	 * 

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

@@ -0,0 +1,97 @@
+/*
+ * Copyright 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 java.util.List;
+
+import org.springframework.hateoas.Link;
+import org.springframework.hateoas.Links;
+import org.springframework.hateoas.ResourceProcessor;
+import org.springframework.hateoas.ResourceSupport;
+import org.springframework.http.HttpEntity;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.util.Assert;
+
+/**
+ * Special {@link ResponseEntity} that exposes {@link Link} instances in the contained {@link ResourceSupport} as link
+ * headers instead of in the body. Note, that this class is not intended to be used directly from user code but by
+ * support code that will transparently invoke the header exposure. If you use this class from a controller directly,
+ * the {@link Link}s will not be present in the {@link ResourceSupport} instance anymore when {@link ResourceProcessor}s
+ * kick in.
+ * 
+ * @author Oliver Gierke
+ */
+public class HeaderLinksResponseEntity<T extends ResourceSupport> extends ResponseEntity<T> {
+
+	/**
+	 * Creates a new {@link HeaderLinksResponseEntity} from the given {@link ResponseEntity}.
+	 * 
+	 * @param entity must not be {@literal null}.
+	 */
+	private HeaderLinksResponseEntity(ResponseEntity<T> entity) {
+
+		super(entity.getBody(), getHeadersWithLinks(entity), entity.getStatusCode());
+		entity.getBody().removeLinks();
+	}
+
+	/**
+	 * Creates a new {@link HeaderLinksResponseEntity} from the given {@link HttpEntity} by defaulting the status code to
+	 * {@link HttpStatus#OK}.
+	 * 
+	 * @param entity must not be {@literal null}.
+	 */
+	private HeaderLinksResponseEntity(HttpEntity<T> entity) {
+		this(new ResponseEntity<T>(entity.getBody(), entity.getHeaders(), HttpStatus.OK));
+	}
+
+	/**
+	 * Wraps the given {@link HttpEntity} into a {@link HeaderLinksResponseEntity}. Will default the status code to
+	 * {@link HttpStatus#OK} if the given value is not a {@link ResponseEntity}.
+	 * 
+	 * @param entity must not be {@literal null}.
+	 * @return
+	 */
+	public static <S extends ResourceSupport> HeaderLinksResponseEntity<S> wrap(HttpEntity<S> entity) {
+
+		Assert.notNull(entity, "Given HttpEntity must not be null!");
+
+		if (entity instanceof ResponseEntity) {
+			return new HeaderLinksResponseEntity<S>((ResponseEntity<S>) entity);
+		} else {
+			return new HeaderLinksResponseEntity<S>(entity);
+		}
+	}
+
+	/**
+	 * Returns the {@link Link}s contained in the {@link ResourceSupport} of the given {@link ResponseEntity} as
+	 * {@link HttpHeaders}.
+	 * 
+	 * @param entity must not be {@literal null}.
+	 * @return
+	 */
+	private static <T extends ResourceSupport> HttpHeaders getHeadersWithLinks(ResponseEntity<T> entity) {
+
+		List<Link> links = entity.getBody().getLinks();
+
+		HttpHeaders httpHeaders = new HttpHeaders();
+		httpHeaders.putAll(entity.getHeaders());
+		httpHeaders.add("Link", new Links(links).toString());
+
+		return httpHeaders;
+	}
+}