DATAGEODE-302 - Declare the GemfireCallback as a @FunctionalInterface.

Edit Javadoc.

Formate source code; optimize imports.

spring-data-geode/src/main/java/org/springframework/data/gemfire/GemfireAccessor.java

@@ -13,23 +13,22 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 package org.springframework.data.gemfire;
 
 import org.apache.geode.GemFireCheckedException;
 import org.apache.geode.GemFireException;
 import org.apache.geode.cache.Region;
 
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
 import org.springframework.beans.factory.InitializingBean;
 import org.springframework.dao.DataAccessException;
 import org.springframework.util.Assert;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 /**
- * {@link GemfireAccessor} is a base class for {@link GemfireTemplate} defining common operations and properties,
- * such as {@link Region}.
+ * {@link GemfireAccessor} is a base class for {@link GemfireTemplate} to encapsulate common operations and properties,
+ * such as accessors to a {@link Region}.
  *
  * This class is not intended to be used directly.
  *
@@ -42,6 +41,7 @@ public class GemfireAccessor implements InitializingBean {
 
 	protected final Logger logger = LoggerFactory.getLogger(getClass());
 
+	@SuppressWarnings("rawtypes")
 	private Region region;
 
 	/**
@@ -54,7 +54,7 @@ public class GemfireAccessor implements InitializingBean {
 	 */
 	@SuppressWarnings("unchecked")
 	public <K, V> Region<K, V> getRegion() {
-		return region;
+		return this.region;
 	}
 
 	/**
@@ -67,6 +67,9 @@ public class GemfireAccessor implements InitializingBean {
 		this.region = region;
 	}
 
+	/**
+	 * @inheritDoc
+	 */
 	public void afterPropertiesSet() {
 		Assert.notNull(getRegion(), "Region is required");
 	}

spring-data-geode/src/main/java/org/springframework/data/gemfire/GemfireCallback.java

@@ -13,7 +13,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 package org.springframework.data.gemfire;
 
 import org.apache.geode.GemFireCheckedException;
@@ -21,7 +20,9 @@ import org.apache.geode.GemFireException;
 import org.apache.geode.cache.Region;
 
 /**
- * Callback interface for GemFire code. To be used with {@link GemfireTemplate}'s execution methods, often as anonymous
+ * Callback interface for GemFire code.
+ *
+ * Implementations of this interface are to be used with {@link GemfireTemplate}'s execution methods, often as anonymous
  * classes within a method implementation. A typical implementation will call Region.get/put/query to perform some
  * operations on stored objects.
  *
@@ -29,25 +30,27 @@ import org.apache.geode.cache.Region;
  * @author John Blum
  * @see org.apache.geode.cache.Region
  */
+@FunctionalInterface
 public interface GemfireCallback<T> {
 
 	/**
-	 * Gets called by {@link GemfireTemplate#execute(GemfireCallback)}. Does not need to care about
-	 * handling transactions or exceptions.
+	 * This methods gets called by {@link GemfireTemplate#execute(GemfireCallback)}.
 	 *
-	 * Allows a result object created within the callback to be returned, i.e. a domain object
-	 * or a collection of domain objects.
+	 * The method implementation does not need to care about handling transactions or exceptions.
 	 *
-	 * A thrown custom RuntimeException is treated as an application exception: it gets propagated to
+	 * Allows a result {@link Object} created within this callback to be returned, i.e. an application domain object
+	 * or a collection of application domain objects.
+	 *
+	 * A custom thrown {@link RuntimeException} is treated as an application exception; the exception is propagated to
 	 * the caller of the template.
 	 *
-	 * @param region the GemFire Cache Region upon which the operation of this callback will be performed.
-	 * @return a result object, or <tt>null</tt> if no result.
-	 * @throws GemFireCheckedException for checked Exceptions occurring in GemFire.
-	 * @throws GemFireException for runtime Exceptions occurring in GemFire.
+	 * @param region {@link Region} on which the operation of this callback will be performed.
+	 * @return a result {@link Object}, or {@literal null} if no result.
+	 * @throws GemFireCheckedException for checked {@link Exception Exceptions} occurring in GemFire.
+	 * @throws GemFireException for {@link RuntimeException RuntimeExceptions} occurring in GemFire.
 	 * @see org.springframework.data.gemfire.GemfireTemplate
 	 * @see org.apache.geode.cache.Region
 	 */
-	T doInGemfire(Region<?,?> region) throws GemFireCheckedException, GemFireException;
+	T doInGemfire(Region<?, ?> region) throws GemFireCheckedException, GemFireException;
 
 }

spring-data-geode/src/main/java/org/springframework/data/gemfire/GenericRegionFactoryBean.java

@@ -13,7 +13,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 package org.springframework.data.gemfire;
 
 /**

spring-data-geode/src/main/java/org/springframework/data/gemfire/support/NoOpBeanFactoryPostProcessor.java

@@ -13,7 +13,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 package org.springframework.data.gemfire.support;
 
 import org.springframework.beans.BeansException;