Add support for using the Apache Geode/Pivotal GemFire o.a.g.cache.CacheLoader interface as a @FunctionalInterface.

Add example implementation of the Apache Geode/Pivotal GemFire o.a.g.cache.CacheLoader interface, which echos the key as the value, dubbed EchoCacheLoader.

geode-spring-boot-starter/src/main/java/org/springframework/boot/data/geode/cache/support/CacheLoaderSupport.java

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+/*
+ * Copyright 2018 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.boot.data.geode.cache.support;
+
+import org.apache.geode.cache.CacheLoader;
+
+/**
+ * The {@link CacheLoaderSupport} interface is an extension of {@link CacheLoader} and a {@link FunctionalInterface}
+ * useful in Lambda expressions.
+ *
+ * @author John Blum
+ * @see org.apache.geode.cache.CacheLoader
+ * @since 1.0.0
+ */
+@FunctionalInterface
+public interface CacheLoaderSupport<K, V> extends CacheLoader<K, V> {
+
+	/**
+	 * Closes any resources opened and used by this {@link CacheLoader}.
+	 *
+	 * @see org.apache.geode.cache.CacheLoader#close()
+	 */
+	@Override
+	default void close() {}
+
+}

geode-spring-boot-starter/src/test/java/example/geode/cache/EchoCacheLoader.java

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+/*
+ * Copyright 2018 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 example.geode.cache;
+
+import org.apache.geode.cache.CacheLoader;
+import org.apache.geode.cache.CacheLoaderException;
+import org.apache.geode.cache.LoaderHelper;
+import org.springframework.boot.data.geode.cache.support.CacheLoaderSupport;
+
+/**
+ * The {@link EchoCacheLoader} class is an implementation of {@link CacheLoader} that echos the key as the value.
+ *
+ * @author John Blum
+ * @see org.springframework.boot.data.geode.cache.support.CacheLoaderSupport
+ * @since 1.0.0
+ */
+@SuppressWarnings("unused")
+public class EchoCacheLoader implements CacheLoaderSupport<String, String> {
+
+	public static final EchoCacheLoader INSTANCE = new EchoCacheLoader();
+
+	@Override
+	public String load(LoaderHelper<String, String> helper) throws CacheLoaderException {
+		return helper.getKey();
+	}
+}