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();
+}