Provide controller level Cache-Control support

Prior to this commit, Cache-Control HTTP headers could be set using
a WebContentInterceptor and configured cache mappings.

This commit adds support for cache-related HTTP headers at the controller
method level, by returning a ResponseEntity instance:

ResponseEntity.status(HttpStatus.OK)
    .cacheControl(CacheControl.maxAge(1, TimeUnit.HOURS).cachePublic())
    .eTag("deadb33f8badf00d")
    .body(entity);

Also, this change now automatically checks the "ETag" and
"Last-Modified" headers in ResponseEntity, in order to respond HTTP
"304 - Not Modified" if necessary.

Issue: SPR-8550

spring-web/src/main/java/org/springframework/http/ResponseEntity.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -59,6 +59,7 @@ import org.springframework.util.ObjectUtils;
  * </pre>
  *
  * @author Arjen Poutsma
+ * @author Brian Clozel
  * @since 3.0.2
  * @see #getStatusCode()
  */
@@ -318,6 +319,20 @@ public class ResponseEntity<T> extends HttpEntity<T> {
 		 */
 		B location(URI location);
 
+		/**
+		 * Set the caching directives for the resource, as specified by the
+		 * {@code Cache-Control} header.
+		 *
+		 * <p>A {@code CacheControl} instance can be built like
+		 * {@code CacheControl.maxAge(3600).cachePublic().noTransform()}.
+		 *
+		 * @param cacheControl the instance that builds cache related HTTP response headers
+		 * @return this builder
+		 * @see <a href="https://tools.ietf.org/html/rfc7234#section-5.2">RFC-7234 Section 5.2</a>
+		 * @since 4.2
+		 */
+		B cacheControl(CacheControl cacheControl);
+
 		/**
 		 * Build the response entity with no body.
 		 * @return the response entity
@@ -423,6 +438,15 @@ public class ResponseEntity<T> extends HttpEntity<T> {
 			return this;
 		}
 
+		@Override
+		public BodyBuilder cacheControl(CacheControl cacheControl) {
+			String ccValue = cacheControl.getHeaderValue();
+			if(ccValue != null) {
+				this.headers.setCacheControl(cacheControl.getHeaderValue());
+			}
+			return this;
+		}
+
 		@Override
 		public ResponseEntity<Void> build() {
 			return new ResponseEntity<Void>(null, this.headers, this.status);