DATACMNS-451 - Added custom CollectionFactory.

Added a Spring Data specific CollectionFactory that augments Spring's CollectionFactory with support for special collection types like EnumSet and EnumMap. For all other types we delegate to the wrapped class.

src/main/java/org/springframework/data/convert/CollectionFactory.java

@@ -0,0 +1,93 @@
+/*
+ * Copyright 2014 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.convert;
+
+import java.util.Collection;
+import java.util.EnumMap;
+import java.util.EnumSet;
+import java.util.Map;
+
+import org.springframework.util.Assert;
+
+/**
+ * Wrapper around Spring's {@link org.springframework.core.CollectionFactory} to add support for additional, sepcial
+ * collection types.
+ * 
+ * @author Oliver Gierke
+ */
+public class CollectionFactory {
+
+	/**
+	 * Creates a new collection instance for the given collection type. Might also inspect the element type in case
+	 * special collections are requested (e.g. {@link EnumSet}).
+	 * 
+	 * @param collectionType must not be {@literal null}.
+	 * @param elementType can be {@literal null}.
+	 * @param size the initial size of the collection to be created.
+	 * @return
+	 */
+	@SuppressWarnings("unchecked")
+	public static Collection<Object> createCollection(Class<?> collectionType, Class<?> elementType, int size) {
+
+		Assert.notNull(collectionType, "Collection type must not be null!");
+
+		if (EnumSet.class.equals(collectionType)) {
+			return EnumSet.noneOf(asEnumType(elementType));
+		}
+
+		return org.springframework.core.CollectionFactory.createCollection(collectionType, size);
+	}
+
+	/**
+	 * Creates a new map instance for the given map type. Might also inspect the key type in case special maps are
+	 * requested (e.g. {@link EnumMap}).
+	 * 
+	 * @param mapType must not be {@literal null}.
+	 * @param keyType can be {@literal null}.
+	 * @param size the initial size of the collection to be created.
+	 * @return
+	 */
+	@SuppressWarnings({ "unchecked", "rawtypes" })
+	public static Map<Object, Object> createMap(Class<?> mapType, Class<?> keyType, int size) {
+
+		Assert.notNull(mapType, "Map type must not be null!");
+
+		if (EnumMap.class.isAssignableFrom(mapType)) {
+			return new EnumMap(asEnumType(keyType));
+		}
+
+		return org.springframework.core.CollectionFactory.createMap(mapType, size);
+	}
+
+	/**
+	 * Returns the given type as subtype of {@link Enum}.
+	 * 
+	 * @param enumType must not be {@literal null}.
+	 * @return
+	 * @throws IllegalArgumentException in case the given type is not a subtype of {@link Enum}.
+	 */
+	@SuppressWarnings("rawtypes")
+	private static Class<? extends Enum> asEnumType(Class<?> enumType) {
+
+		Assert.notNull(enumType, "EnumType must not be null!");
+
+		if (!Enum.class.isAssignableFrom(enumType)) {
+			throw new IllegalArgumentException(String.format("Given type %s is not an enum type!", enumType.getName()));
+		}
+
+		return enumType.asSubclass(Enum.class);
+	}
+}