SGF-515 - Add methods to return null-safe arrays, Lists, Maps and Sets.

Add method to convert an array of elements into an unmodifiable Set.

src/main/java/org/springframework/data/gemfire/support/ConnectionEndpointList.java

@@ -99,7 +99,7 @@ public class ConnectionEndpointList extends AbstractList<ConnectionEndpoint> {
 	public static ConnectionEndpointList parse(int defaultPort, String... hostsPorts) {
 		List<ConnectionEndpoint> connectionEndpoints = new ArrayList<ConnectionEndpoint>(hostsPorts.length);
 
-		for (String hostPort : ArrayUtils.nullSafeArray(hostsPorts)) {
+		for (String hostPort : ArrayUtils.nullSafeArray(hostsPorts, String.class)) {
 			connectionEndpoints.add(ConnectionEndpoint.parse(hostPort, defaultPort));
 		}
 

src/main/java/org/springframework/data/gemfire/util/ArrayUtils.java

@@ -79,16 +79,18 @@ public abstract class ArrayUtils {
 	}
 
 	/**
-	 * Null-safe, empty array operation returning the given Object array if not null or an empty Object array
+	 * Null-safe, empty array operation returning the given object array if not null or an empty object array
 	 * if the array argument is null.
 	 *
-	 * @param <T> the element Class type of the array.
-	 * @param array the Object array on which a null check is performed.
-	 * @return the given Object array if not null, otherwise return an empty Object array.
+	 * @param <T> Class type of the array elements.
+	 * @param array array of objects on which a null check is performed.
+	 * @param componentType Class type of the array elements.
+	 * @return the given object array if not null, otherwise return an empty object array.
+	 * @see java.lang.reflect.Array#newInstance(Class, int)
 	 */
 	@SuppressWarnings("unchecked")
-	public static <T> T[] nullSafeArray(T[] array) {
-		return (array != null ? array : (T[]) new Object[0]);
+	public static <T> T[] nullSafeArray(T[] array, Class<T> componentType) {
+		return (array != null ? array : (T[]) Array.newInstance(componentType, 0));
 	}
 
 	/**

src/main/java/org/springframework/data/gemfire/util/CollectionUtils.java

@@ -19,8 +19,12 @@ package org.springframework.data.gemfire.util;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Enumeration;
+import java.util.HashSet;
 import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
 import java.util.NoSuchElementException;
+import java.util.Set;
 
 /**
  * The CollectionUtils class is a utility class for working with Java Collections Framework and classes.
@@ -28,12 +32,28 @@ import java.util.NoSuchElementException;
  * @author John Blum
  * @see java.util.Collection
  * @see java.util.Collections
+ * @see java.util.List
+ * @see java.util.Map
+ * @see java.util.Set
  * @see org.springframework.util.CollectionUtils
  * @since 1.7.0
  */
 @SuppressWarnings("unused")
 public abstract class CollectionUtils extends org.springframework.util.CollectionUtils {
 
+	/**
+	 * Returns an unmodifiable {@link Set} containing the elements from the given object array.
+	 *
+	 * @param <T> Class type of the elements.
+	 * @param elements array of objects to add to the {@link Set}.
+	 * @return an unmodifiable {@link Set} containing the elements from the given object array.
+	 */
+	public static <T> Set<T> asSet(T... elements) {
+		Set<T> set = new HashSet<T>(elements.length);
+		Collections.addAll(set, elements);
+		return Collections.unmodifiableSet(set);
+	}
+
 	/**
 	 * Adapts the given Enumeration as an Iterable object for use within a for each loop.
 	 *
@@ -69,12 +89,13 @@ public abstract class CollectionUtils extends org.springframework.util.Collectio
 	}
 
 	/**
-	 * A null-safe operation returning the original Collection if non-null or an empty Collection
-	 * (implemented with List) if null.
+	 * Null-safe operation returning the given {@link Collection} if not {@literal null}
+	 * or an empty {@link Collection} (implemented with {@link List}) if {@literal null}.
 	 *
-	 * @param <T> the element class type of the Collection.
-	 * @param collection the Collection to evaluate for being null.
-	 * @return the given Collection if not null, otherwise return an empty Collection (List).
+	 * @param <T> Class type of the {@link Collection} elements.
+	 * @param collection {@link Collection} to evaluate.
+	 * @return the given {@link Collection} if not null or return an empty {@link Collection}
+	 * (implemented with {@link List}).
 	 * @see java.util.Collections#emptyList()
 	 */
 	public static <T> Collection<T> nullSafeCollection(Collection<T> collection) {
@@ -110,4 +131,44 @@ public abstract class CollectionUtils extends org.springframework.util.Collectio
 			}
 		});
 	}
+
+	/**
+	 * Null-safe operation returning the given {@link List} if not {@literal null}
+	 * or an empty {@link List} if {@literal null}.
+	 *
+	 * @param <T> Class type of the {@link List} elements.
+	 * @param list {@link List} to evaluate.
+	 * @return the given {@link List} if not null or an empty {@link List}.
+	 * @see java.util.Collections#emptyList()
+	 */
+	public static <T> List<T> nullSafeList(List<T> list) {
+		return (list != null ? list : Collections.<T>emptyList());
+	}
+
+	/**
+	 * Null-safe operation returning the given {@link Map} if not {@literal null}
+	 * or an empty {@link Map} if {@literal null}.
+	 *
+	 * @param <K> Class type of the {@link Map Map's} keys.
+	 * @param <V> Class type of the {@link Map Map's} values.
+	 * @param map {@link Map} to evaluate.
+	 * @return the given {@link Map} if not null or an empty {@link Map}.
+	 * @see java.util.Collections#emptyMap()
+	 */
+	public static <K, V> Map<K, V> nullSafeMap(Map<K, V> map) {
+		return (map != null ? map : Collections.<K, V>emptyMap());
+	}
+
+	/**
+	 * Null-safe operation returning the given {@link Set} if not {@literal null}
+	 * or an empty {@link Set} if {@literal null}.
+	 *
+	 * @param <T> Class type of the {@link Set} elements.
+	 * @param set {@link Set} to evaluate.
+	 * @return the given {@link Set} if not null or an empty {@link Set}.
+	 * @see java.util.Collections#emptySet()
+	 */
+	public static <T> Set<T> nullSafeSet(Set<T> set) {
+		return (set != null ? set : Collections.<T>emptySet());
+	}
 }