DATAREST-835 - Search resources returning a single resource now get and consider ETag and Last-Modified headers.

We now interpret If-None-Match and If-Modified-Since headers on requests to resources backed by query methods returning a single instance only. This allows clients to optimize GET requests to those resources to save bandwidth.

spring-data-rest-core/src/main/java/org/springframework/data/rest/core/util/Supplier.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2016 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.data.rest.core.util;
+
+/**
+ * Mimics Java 8's Supplier interface to allow deferring a computation.
+ * 
+ * @author Oliver Gierke
+ * @since 2.6
+ * @soundtrack KRS-One - Sound Of Da Police (Return Of The Boom Bap)
+ */
+public interface Supplier<T> {
+
+	T get();
+}

spring-data-rest-tests/spring-data-rest-tests-jpa/src/test/java/org/springframework/data/rest/webmvc/RepositoryEntityControllerIntegrationTests.java

@@ -42,12 +42,12 @@ import org.springframework.data.rest.webmvc.support.DefaultedPageable;
 import org.springframework.data.rest.webmvc.support.ETag;
 import org.springframework.hateoas.Resource;
 import org.springframework.http.HttpEntity;
+import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
 import org.springframework.http.ResponseEntity;
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.transaction.annotation.Transactional;
-import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.web.HttpRequestMethodNotSupportedException;
 
 /**
@@ -273,7 +273,7 @@ public class RepositoryEntityControllerIntegrationTests extends AbstractControll
 		Mockito.when(assembler.toFullResource(Mockito.any(Object.class))).thenReturn(resource);
 
 		ResponseEntity<Resource<?>> entity = controller.getItemResource(getResourceInformation(Address.class), address.id,
-				assembler, new LinkedMultiValueMap<String, String>());
+				assembler, new HttpHeaders());
 
 		assertThat(entity.getHeaders().getETag(), is(notNullValue()));
 	}

spring-data-rest-tests/spring-data-rest-tests-jpa/src/test/java/org/springframework/data/rest/webmvc/RepositorySearchControllerIntegrationTests.java

@@ -39,6 +39,7 @@ import org.springframework.hateoas.PagedResources;
 import org.springframework.hateoas.ResourceSupport;
 import org.springframework.hateoas.Resources;
 import org.springframework.http.HttpEntity;
+import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.ResponseEntity;
 import org.springframework.test.context.ContextConfiguration;
@@ -100,8 +101,8 @@ public class RepositorySearchControllerIntegrationTests extends AbstractControll
 		MultiValueMap<String, Object> parameters = new LinkedMultiValueMap<String, Object>(1);
 		parameters.add("firstname", "John");
 
-		ResponseEntity<Object> response = controller.executeSearch(resourceInformation, parameters, "firstname", PAGEABLE,
-				null, assembler);
+		ResponseEntity<?> response = controller.executeSearch(resourceInformation, parameters, "firstname", PAGEABLE, null,
+				assembler, new HttpHeaders());
 
 		ResourceTester tester = ResourceTester.of(response.getBody());
 		PagedResources<Object> pagedResources = tester.assertIsPage();
@@ -190,8 +191,8 @@ public class RepositorySearchControllerIntegrationTests extends AbstractControll
 
 		RootResourceInformation resourceInformation = getResourceInformation(Book.class);
 
-		ResponseEntity<Object> result = controller.executeSearch(resourceInformation, parameters, "findByAuthorsContains",
-				PAGEABLE, null, assembler);
+		ResponseEntity<?> result = controller.executeSearch(resourceInformation, parameters, "findByAuthorsContains",
+				PAGEABLE, null, assembler, new HttpHeaders());
 
 		assertThat(result.getBody(), is(instanceOf(Resources.class)));
 	}

spring-data-rest-tests/spring-data-rest-tests-mongodb/src/main/java/org/springframework/data/rest/tests/mongodb/Profile.java

@@ -21,6 +21,7 @@ import java.util.Map;
 
 import org.springframework.data.annotation.Id;
 import org.springframework.data.annotation.LastModifiedDate;
+import org.springframework.data.annotation.Version;
 import org.springframework.data.mongodb.core.mapping.Document;
 
 import com.fasterxml.jackson.annotation.JsonIgnore;
@@ -36,6 +37,7 @@ public class Profile {
 	private Long person;
 	private @JsonProperty(required = true) String type;
 	private @LastModifiedDate Date lastModifiedDate;
+	private @Version Long version;
 	private @JsonProperty("renamed") String aliased;
 	private Map<String, String> metadata = new HashMap<String, String>();
 

spring-data-rest-tests/spring-data-rest-tests-mongodb/src/test/java/org/springframework/data/rest/tests/mongodb/MongoWebTests.java

@@ -343,4 +343,34 @@ public class MongoWebTests extends CommonWebTests {
 
 		mvc.perform(get(href)).andExpect(status().isOk());
 	}
+
+	/**
+	 * @see DATAREST-835
+	 */
+	@Test
+	public void exposesETagHeaderForSearchResourceYieldingItemResource() throws Exception {
+
+		Link link = client.discoverUnique("profiles", "search", "findById");
+
+		Profile profile = repository.findAll().iterator().next();
+
+		mvc.perform(get(link.expand(profile.getId()).getHref()))//
+				.andExpect(header().string("ETag", is("\"0\"")))//
+				.andExpect(header().string("Last-Modified", is(notNullValue())));
+	}
+
+	/**
+	 * @see DATAREST-835
+	 */
+	@Test
+	public void doesNotAddETagHeaderForCollectionQueryResource() throws Exception {
+
+		Link link = client.discoverUnique("profiles", "search", "findByType");
+
+		Profile profile = repository.findAll().iterator().next();
+
+		mvc.perform(get(link.expand(profile.getType()).getHref()))//
+				.andExpect(header().string("ETag", is(nullValue())))//
+				.andExpect(header().string("Last-Modified", is(nullValue())));
+	}
 }

spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/AbstractRepositoryRestController.java

@@ -27,11 +27,9 @@ import org.springframework.data.rest.core.mapping.ResourceMetadata;
 import org.springframework.data.web.PagedResourcesAssembler;
 import org.springframework.hateoas.Link;
 import org.springframework.hateoas.Resource;
-import org.springframework.hateoas.ResourceSupport;
 import org.springframework.hateoas.Resources;
 import org.springframework.hateoas.core.EmbeddedWrappers;
 import org.springframework.util.Assert;
-import org.springframework.util.ClassUtils;
 import org.springframework.web.servlet.support.ServletUriComponentsBuilder;
 
 /**
@@ -83,30 +81,6 @@ class AbstractRepositoryRestController {
 		}
 	}
 
-	/**
-	 * Turns the given source into a {@link ResourceSupport} if needed and possible. Uses the given
-	 * {@link PersistentEntityResourceAssembler} for the actual conversion.
-	 * 
-	 * @param source can be must not be {@literal null}.
-	 * @param assembler must not be {@literal null}.
-	 * @param domainType the domain type in case the source is an empty iterable, must not be {@literal null}.
-	 * @param baseLink can be {@literal null}.
-	 * @return
-	 */
-	protected Object toResource(Object source, PersistentEntityResourceAssembler assembler, Class<?> domainType,
-			Link baseLink) {
-
-		if (source instanceof Iterable) {
-			return toResources((Iterable<?>) source, assembler, domainType, baseLink);
-		} else if (source == null) {
-			throw new ResourceNotFoundException();
-		} else if (ClassUtils.isPrimitiveOrWrapper(source.getClass())) {
-			return source;
-		}
-
-		return assembler.toFullResource(source);
-	}
-
 	protected Resources<?> entitiesToResources(Page<Object> page, PersistentEntityResourceAssembler assembler,
 			Class<?> domainType, Link baseLink) {
 

spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/RepositoryEntityController.java

@@ -44,6 +44,7 @@ import org.springframework.data.rest.core.mapping.ResourceMetadata;
 import org.springframework.data.rest.core.mapping.ResourceType;
 import org.springframework.data.rest.core.mapping.SearchResourceMappings;
 import org.springframework.data.rest.core.mapping.SupportedHttpMethods;
+import org.springframework.data.rest.core.util.Supplier;
 import org.springframework.data.rest.webmvc.support.BackendId;
 import org.springframework.data.rest.webmvc.support.DefaultedPageable;
 import org.springframework.data.rest.webmvc.support.ETag;
@@ -62,7 +63,6 @@ import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
 import org.springframework.http.ResponseEntity;
-import org.springframework.util.MultiValueMap;
 import org.springframework.web.HttpRequestMethodNotSupportedException;
 import org.springframework.web.bind.annotation.RequestHeader;
 import org.springframework.web.bind.annotation.RequestMapping;
@@ -90,6 +90,7 @@ class RepositoryEntityController extends AbstractRepositoryRestController implem
 	private final RepositoryEntityLinks entityLinks;
 	private final RepositoryRestConfiguration config;
 	private final HttpHeadersPreparer headersPreparer;
+	private final ResourceStatus resourceStatus;
 
 	private ApplicationEventPublisher publisher;
 
@@ -107,13 +108,14 @@ class RepositoryEntityController extends AbstractRepositoryRestController implem
 	@Autowired
 	public RepositoryEntityController(Repositories repositories, RepositoryRestConfiguration config,
 			RepositoryEntityLinks entityLinks, PagedResourcesAssembler<Object> assembler,
-			AuditableBeanWrapperFactory auditableBeanWrapperFactory) {
+			HttpHeadersPreparer headersPreparer) {
 
 		super(assembler);
 
 		this.entityLinks = entityLinks;
 		this.config = config;
-		this.headersPreparer = new HttpHeadersPreparer(auditableBeanWrapperFactory);
+		this.headersPreparer = headersPreparer;
+		this.resourceStatus = ResourceStatus.of(headersPreparer);
 	}
 
 	/*
@@ -187,7 +189,7 @@ class RepositoryEntityController extends AbstractRepositoryRestController implem
 	@RequestMapping(value = BASE_MAPPING, method = RequestMethod.GET)
 	public Resources<?> getCollectionResource(@QuerydslPredicate RootResourceInformation resourceInformation,
 			DefaultedPageable pageable, Sort sort, PersistentEntityResourceAssembler assembler)
-					throws ResourceNotFoundException, HttpRequestMethodNotSupportedException {
+			throws ResourceNotFoundException, HttpRequestMethodNotSupportedException {
 
 		resourceInformation.verifySupportedMethod(HttpMethod.GET, ResourceType.COLLECTION);
 
@@ -232,7 +234,7 @@ class RepositoryEntityController extends AbstractRepositoryRestController implem
 			produces = { "application/x-spring-data-compact+json", "text/uri-list" })
 	public Resources<?> getCollectionResourceCompact(@QuerydslPredicate RootResourceInformation resourceinformation,
 			DefaultedPageable pageable, Sort sort, PersistentEntityResourceAssembler assembler)
-					throws ResourceNotFoundException, HttpRequestMethodNotSupportedException {
+			throws ResourceNotFoundException, HttpRequestMethodNotSupportedException {
 
 		Resources<?> resources = getCollectionResource(resourceinformation, pageable, sort, assembler);
 		List<Link> links = new ArrayList<Link>(resources.getLinks());
@@ -263,7 +265,7 @@ class RepositoryEntityController extends AbstractRepositoryRestController implem
 	public ResponseEntity<ResourceSupport> postCollectionResource(RootResourceInformation resourceInformation,
 			PersistentEntityResource payload, PersistentEntityResourceAssembler assembler,
 			@RequestHeader(value = ACCEPT_HEADER, required = false) String acceptHeader)
-					throws HttpRequestMethodNotSupportedException {
+			throws HttpRequestMethodNotSupportedException {
 
 		resourceInformation.verifySupportedMethod(HttpMethod.POST, ResourceType.COLLECTION);
 
@@ -327,37 +329,24 @@ class RepositoryEntityController extends AbstractRepositoryRestController implem
 	 */
 	@RequestMapping(value = BASE_MAPPING + "/{id}", method = RequestMethod.GET)
 	public ResponseEntity<Resource<?>> getItemResource(RootResourceInformation resourceInformation,
-			@BackendId Serializable id, PersistentEntityResourceAssembler assembler,
-			@RequestHeader MultiValueMap<String, String> rawHeaders) throws HttpRequestMethodNotSupportedException {
+			@BackendId Serializable id, final PersistentEntityResourceAssembler assembler, @RequestHeader HttpHeaders headers)
+			throws HttpRequestMethodNotSupportedException {
 
-		Object domainObj = getItemResource(resourceInformation, id);
+		final Object domainObj = getItemResource(resourceInformation, id);
 
 		if (domainObj == null) {
 			return new ResponseEntity<Resource<?>>(HttpStatus.NOT_FOUND);
 		}
 
-		HttpHeaders headers = new HttpHeaders();
-		headers.putAll(rawHeaders);
-
-		// Check ETag for If-Non-Match
-
-		List<String> ifNoneMatch = headers.getIfNoneMatch();
-		ETag eTag = ifNoneMatch.isEmpty() ? ETag.NO_ETAG : ETag.from(ifNoneMatch.get(0));
 		PersistentEntity<?, ?> entity = resourceInformation.getPersistentEntity();
-		HttpHeaders responseHeaders = headersPreparer.prepareHeaders(entity, domainObj);
 
-		if (eTag.matches(entity, domainObj)) {
-			return new ResponseEntity<Resource<?>>(responseHeaders, HttpStatus.NOT_MODIFIED);
-		}
-
-		// Check last modification for If-Modified-Since
-
-		if (headersPreparer.isObjectStillValid(domainObj, headers)) {
-			return new ResponseEntity<Resource<?>>(responseHeaders, HttpStatus.NOT_MODIFIED);
-		}
-
-		PersistentEntityResource resource = assembler.toFullResource(domainObj);
-		return new ResponseEntity<Resource<?>>(resource, responseHeaders, HttpStatus.OK);
+		return resourceStatus.getStatusAndHeaders(headers, domainObj, entity).toResponseEntity(//
+				new Supplier<PersistentEntityResource>() {
+					@Override
+					public PersistentEntityResource get() {
+						return assembler.toFullResource(domainObj);
+					}
+				});
 	}
 
 	/**
@@ -376,7 +365,7 @@ class RepositoryEntityController extends AbstractRepositoryRestController implem
 	public ResponseEntity<? extends ResourceSupport> putItemResource(RootResourceInformation resourceInformation,
 			PersistentEntityResource payload, @BackendId Serializable id, PersistentEntityResourceAssembler assembler,
 			ETag eTag, @RequestHeader(value = ACCEPT_HEADER, required = false) String acceptHeader)
-					throws HttpRequestMethodNotSupportedException {
+			throws HttpRequestMethodNotSupportedException {
 
 		resourceInformation.verifySupportedMethod(HttpMethod.PUT, ResourceType.ITEM);
 
@@ -406,7 +395,7 @@ class RepositoryEntityController extends AbstractRepositoryRestController implem
 	public ResponseEntity<ResourceSupport> patchItemResource(RootResourceInformation resourceInformation,
 			PersistentEntityResource payload, @BackendId Serializable id, PersistentEntityResourceAssembler assembler,
 			ETag eTag, @RequestHeader(value = ACCEPT_HEADER, required = false) String acceptHeader)
-					throws HttpRequestMethodNotSupportedException, ResourceNotFoundException {
+			throws HttpRequestMethodNotSupportedException, ResourceNotFoundException {
 
 		resourceInformation.verifySupportedMethod(HttpMethod.PATCH, ResourceType.ITEM);
 

spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/RepositorySearchController.java

@@ -28,12 +28,14 @@ import java.util.Map.Entry;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.core.MethodParameter;
 import org.springframework.data.domain.Sort;
+import org.springframework.data.mapping.PersistentEntity;
 import org.springframework.data.repository.query.Param;
 import org.springframework.data.repository.support.RepositoryInvoker;
 import org.springframework.data.rest.core.mapping.MethodResourceMapping;
 import org.springframework.data.rest.core.mapping.ResourceMappings;
 import org.springframework.data.rest.core.mapping.ResourceMetadata;
 import org.springframework.data.rest.core.mapping.SearchResourceMappings;
+import org.springframework.data.rest.core.util.Supplier;
 import org.springframework.data.rest.webmvc.support.DefaultedPageable;
 import org.springframework.data.rest.webmvc.support.RepositoryEntityLinks;
 import org.springframework.data.util.ClassTypeInformation;
@@ -53,9 +55,11 @@ import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
 import org.springframework.util.Assert;
+import org.springframework.util.ClassUtils;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.RequestHeader;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RequestMethod;
 import org.springframework.web.bind.annotation.RequestParam;
@@ -75,6 +79,7 @@ class RepositorySearchController extends AbstractRepositoryRestController {
 
 	private final RepositoryEntityLinks entityLinks;
 	private final ResourceMappings mappings;
+	private ResourceStatus resourceStatus;
 
 	/**
 	 * Creates a new {@link RepositorySearchController} using the given {@link PagedResourcesAssembler},
@@ -86,7 +91,7 @@ class RepositorySearchController extends AbstractRepositoryRestController {
 	 */
 	@Autowired
 	public RepositorySearchController(PagedResourcesAssembler<Object> assembler, RepositoryEntityLinks entityLinks,
-			ResourceMappings mappings) {
+			ResourceMappings mappings, HttpHeadersPreparer headersPreparer) {
 
 		super(assembler);
 
@@ -95,6 +100,7 @@ class RepositorySearchController extends AbstractRepositoryRestController {
 
 		this.entityLinks = entityLinks;
 		this.mappings = mappings;
+		this.resourceStatus = ResourceStatus.of(headersPreparer);
 	}
 
 	/**
@@ -112,7 +118,7 @@ class RepositorySearchController extends AbstractRepositoryRestController {
 		HttpHeaders headers = new HttpHeaders();
 		headers.setAllow(Collections.singleton(HttpMethod.GET));
 
-		return new ResponseEntity<Object>(headers, HttpStatus.OK);
+		return ResponseEntity.ok().headers(headers).build();
 	}
 
 	/**
@@ -126,7 +132,7 @@ class RepositorySearchController extends AbstractRepositoryRestController {
 
 		verifySearchesExposed(resourceInformation);
 
-		return new ResponseEntity<Object>(HttpStatus.NO_CONTENT);
+		return ResponseEntity.noContent().build();
 	}
 
 	/**
@@ -169,9 +175,9 @@ class RepositorySearchController extends AbstractRepositoryRestController {
 	 */
 	@ResponseBody
 	@RequestMapping(value = BASE_MAPPING + "/{search}", method = RequestMethod.GET)
-	public ResponseEntity<Object> executeSearch(RootResourceInformation resourceInformation,
+	public ResponseEntity<?> executeSearch(RootResourceInformation resourceInformation,
 			@RequestParam MultiValueMap<String, Object> parameters, @PathVariable String search, DefaultedPageable pageable,
-			Sort sort, PersistentEntityResourceAssembler assembler) {
+			Sort sort, PersistentEntityResourceAssembler assembler, @RequestHeader HttpHeaders headers) {
 
 		Method method = checkExecutability(resourceInformation, search);
 		Object result = executeQueryMethod(resourceInformation.getInvoker(), parameters, method, pageable, sort, assembler);
@@ -180,7 +186,40 @@ class RepositorySearchController extends AbstractRepositoryRestController {
 		MethodResourceMapping methodMapping = searchMappings.getExportedMethodMappingForPath(search);
 		Class<?> domainType = methodMapping.getReturnedDomainType();
 
-		return new ResponseEntity<Object>(toResource(result, assembler, domainType, null), HttpStatus.OK);
+		return toResource(result, assembler, domainType, null, headers, resourceInformation);
+	}
+
+	/**
+	 * Turns the given source into a {@link ResourceSupport} if needed and possible. Uses the given
+	 * {@link PersistentEntityResourceAssembler} for the actual conversion.
+	 * 
+	 * @param source can be must not be {@literal null}.
+	 * @param assembler must not be {@literal null}.
+	 * @param domainType the domain type in case the source is an empty iterable, must not be {@literal null}.
+	 * @param baseLink can be {@literal null}.
+	 * @return
+	 */
+	protected ResponseEntity<?> toResource(final Object source, final PersistentEntityResourceAssembler assembler,
+			Class<?> domainType, Link baseLink, HttpHeaders headers, RootResourceInformation information) {
+
+		if (source instanceof Iterable) {
+			return ResponseEntity.ok(toResources((Iterable<?>) source, assembler, domainType, baseLink));
+		} else if (source == null) {
+			throw new ResourceNotFoundException();
+		} else if (ClassUtils.isPrimitiveOrWrapper(source.getClass())) {
+			return ResponseEntity.ok(source);
+		}
+
+		PersistentEntity<?, ?> entity = information.getPersistentEntity();
+
+		return resourceStatus.getStatusAndHeaders(headers, source, entity).toResponseEntity(//
+				new Supplier<PersistentEntityResource>() {
+
+					@Override
+					public PersistentEntityResource get() {
+						return assembler.toFullResource(source);
+					}
+				});
 	}
 
 	/**
@@ -199,13 +238,17 @@ class RepositorySearchController extends AbstractRepositoryRestController {
 	@RequestMapping(value = BASE_MAPPING + "/{search}", method = RequestMethod.GET, //
 			produces = { "application/x-spring-data-compact+json" })
 	public ResourceSupport executeSearchCompact(RootResourceInformation resourceInformation,
-			@RequestParam MultiValueMap<String, Object> parameters, @PathVariable String repository,
-			@PathVariable String search, DefaultedPageable pageable, Sort sort, PersistentEntityResourceAssembler assembler) {
+			@RequestHeader HttpHeaders headers, @RequestParam MultiValueMap<String, Object> parameters,
+			@PathVariable String repository, @PathVariable String search, DefaultedPageable pageable, Sort sort,
+			PersistentEntityResourceAssembler assembler) {
 
 		Method method = checkExecutability(resourceInformation, search);
 		Object result = executeQueryMethod(resourceInformation.getInvoker(), parameters, method, pageable, sort, assembler);
 		ResourceMetadata metadata = resourceInformation.getResourceMetadata();
-		Object resource = toResource(result, assembler, metadata.getDomainType(), null);
+		ResponseEntity<?> entity = toResource(result, assembler, metadata.getDomainType(), null, headers,
+				resourceInformation);
+		Object resource = entity.getBody();
+
 		List<Link> links = new ArrayList<Link>();
 
 		if (resource instanceof Resources && ((Resources<?>) resource).getContent() != null) {

spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/ResourceStatus.java

@@ -0,0 +1,96 @@
+/*
+ * Copyright 2016 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.data.rest.webmvc;
+
+import lombok.AccessLevel;
+import lombok.Getter;
+import lombok.NonNull;
+import lombok.RequiredArgsConstructor;
+
+import java.util.List;
+
+import org.springframework.data.mapping.PersistentEntity;
+import org.springframework.data.rest.core.util.Supplier;
+import org.springframework.data.rest.webmvc.support.ETag;
+import org.springframework.hateoas.Resource;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+
+/**
+ * Simple abstraction to capture the status of a resource to determine whether it has been modified or not and produce
+ * {@link ResponseEntity} via its {@link StatusAndHeaders} sub component.
+ * 
+ * @author Oliver Gierke
+ * @since 2.6
+ * @soundtrack Blumentopf - Dass ich nicht lache (Kein Zufall)
+ */
+@RequiredArgsConstructor(staticName = "of")
+class ResourceStatus {
+
+	private final @NonNull HttpHeadersPreparer preparer;
+
+	/**
+	 * Returns the {@link StatusAndHeaders} calculated from the given {@link HttpHeaders}, domain object and
+	 * {@link RootResourceInformation.
+	 * 
+	 * @param requestHeaders must not be {@literal null}.
+	 * @param domainObject must not be {@literal null}.
+	 * @param information
+	 * @return
+	 */
+	public StatusAndHeaders getStatusAndHeaders(HttpHeaders requestHeaders, Object domainObject,
+			PersistentEntity<?, ?> entity) {
+
+		// Check ETag for If-Non-Match
+
+		List<String> ifNoneMatch = requestHeaders.getIfNoneMatch();
+		ETag eTag = ifNoneMatch.isEmpty() ? ETag.NO_ETAG : ETag.from(ifNoneMatch.get(0));
+		HttpHeaders responseHeaders = preparer.prepareHeaders(entity, domainObject);
+
+		// Check last modification for If-Modified-Since
+
+		return eTag.matches(entity, domainObject) || preparer.isObjectStillValid(domainObject, requestHeaders)
+				? StatusAndHeaders.notModified(responseHeaders) : StatusAndHeaders.modified(responseHeaders);
+	}
+
+	@RequiredArgsConstructor(access = AccessLevel.PRIVATE)
+	public static class StatusAndHeaders {
+
+		private final @NonNull HttpHeaders headers;
+		private final @Getter(AccessLevel.PACKAGE) boolean modified;
+
+		private static StatusAndHeaders notModified(HttpHeaders headers) {
+			return new StatusAndHeaders(headers, false);
+		}
+
+		private static StatusAndHeaders modified(HttpHeaders headers) {
+			return new StatusAndHeaders(headers, true);
+		}
+
+		/**
+		 * Creates a {@link ResponseEntity} based on the given {@link PersistentEntityResource}.
+		 * 
+		 * @param supplier a {@link Supplier} to provide a {@link PersistentEntityResource} eventually, must not be
+		 *          {@literal null}.
+		 * @return
+		 */
+		public ResponseEntity<Resource<?>> toResponseEntity(Supplier<PersistentEntityResource> supplier) {
+			return modified ? new ResponseEntity<Resource<?>>(supplier.get(), headers, HttpStatus.OK)
+					: new ResponseEntity<Resource<?>>(headers, HttpStatus.NOT_MODIFIED);
+		}
+	}
+}

spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/config/RepositoryRestMvcConfiguration.java

@@ -77,6 +77,7 @@ import org.springframework.data.rest.webmvc.BasePathAwareController;
 import org.springframework.data.rest.webmvc.BasePathAwareHandlerMapping;
 import org.springframework.data.rest.webmvc.BaseUri;
 import org.springframework.data.rest.webmvc.EmbeddedResourcesAssembler;
+import org.springframework.data.rest.webmvc.HttpHeadersPreparer;
 import org.springframework.data.rest.webmvc.ProfileResourceProcessor;
 import org.springframework.data.rest.webmvc.RepositoryRestController;
 import org.springframework.data.rest.webmvc.RepositoryRestExceptionHandler;
@@ -773,6 +774,11 @@ public class RepositoryRestMvcConfiguration extends HateoasAwareSpringDataWebCon
 		return new MappingAuditableBeanWrapperFactory(persistentEntities());
 	}
 
+	@Bean
+	public HttpHeadersPreparer httpHeadersPreparer() {
+		return new HttpHeadersPreparer(auditableBeanWrapperFactory());
+	}
+
 	@Bean
 	public SelfLinkProvider selfLinkProvider() {
 		return new DefaultSelfLinkProvider(persistentEntities(), entityLinks(), getEntityLookups());

spring-data-rest-webmvc/src/test/java/org/springframework/data/rest/webmvc/ResourceStatusUnitTests.java

@@ -0,0 +1,120 @@
+/*
+ * Copyright 2016 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.data.rest.webmvc;
+
+import static org.hamcrest.CoreMatchers.*;
+import static org.junit.Assert.*;
+import static org.mockito.Matchers.*;
+import static org.mockito.Mockito.*;
+
+import lombok.Value;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Matchers;
+import org.mockito.Mock;
+import org.mockito.runners.MockitoJUnitRunner;
+import org.springframework.data.annotation.Version;
+import org.springframework.data.keyvalue.core.mapping.KeyValuePersistentEntity;
+import org.springframework.data.keyvalue.core.mapping.context.KeyValueMappingContext;
+import org.springframework.data.rest.core.util.Supplier;
+import org.springframework.data.rest.webmvc.ResourceStatus.StatusAndHeaders;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatus;
+
+/**
+ * Unit tests for {@link ResourceStatus}.
+ * 
+ * @author Oliver Gierke
+ */
+@RunWith(MockitoJUnitRunner.class)
+public class ResourceStatusUnitTests {
+
+	ResourceStatus status;
+	KeyValuePersistentEntity<?> entity;
+
+	@Mock HttpHeadersPreparer preparer;
+	@Mock Supplier<PersistentEntityResource> supplier;
+
+	@Before
+	public void setUp() {
+
+		this.status = ResourceStatus.of(preparer);
+
+		KeyValueMappingContext context = new KeyValueMappingContext();
+		this.entity = context.getPersistentEntity(Sample.class);
+
+		doReturn(new HttpHeaders()).when(preparer).prepareHeaders(eq(entity), Matchers.any());
+	}
+
+	/**
+	 * @see DATAREST-835
+	 */
+	@Test(expected = IllegalArgumentException.class)
+	public void rejectsNullPreparer() {
+		ResourceStatus.of(null);
+	}
+
+	/**
+	 * @see DATAREST-835
+	 */
+	@Test
+	public void returnsModifiedIfNoHeadersGiven() {
+		assertModified(status.getStatusAndHeaders(new HttpHeaders(), new Sample(0), entity));
+	}
+
+	/**
+	 * @see DATAREST-835
+	 */
+	@Test
+	public void returnsNotModifiedForEntityWithRequestedETag() {
+
+		HttpHeaders headers = new HttpHeaders();
+		headers.setIfNoneMatch("\"1\"");
+
+		assertNotModified(status.getStatusAndHeaders(headers, new Sample(1), entity));
+	}
+
+	/**
+	 * @see DATAREST-835
+	 */
+	@Test
+	public void returnsNotModifiedIfEntityIsStillConsideredValid() {
+
+		doReturn(true).when(preparer).isObjectStillValid(Matchers.any(), Matchers.any(HttpHeaders.class));
+
+		assertNotModified(status.getStatusAndHeaders(new HttpHeaders(), new Sample(0), entity));
+	}
+
+	private void assertModified(StatusAndHeaders statusAndHeaders) {
+
+		assertThat(statusAndHeaders.isModified(), is(true));
+		assertThat(statusAndHeaders.toResponseEntity(supplier).getStatusCode(), is(HttpStatus.OK));
+		verify(supplier).get();
+	}
+
+	private void assertNotModified(StatusAndHeaders statusAndHeaders) {
+
+		assertThat(statusAndHeaders.isModified(), is(false));
+		assertThat(statusAndHeaders.toResponseEntity(supplier).getStatusCode(), is(HttpStatus.NOT_MODIFIED));
+	}
+
+	@Value
+	static class Sample {
+		@Version int version;
+	}
+}