- /*
- * Copyright 2003-2004 The Apache Software Foundation
- *
- * 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.apache.commons.collections.map;
-
- import java.io.IOException;
- import java.io.ObjectInputStream;
- import java.io.ObjectOutputStream;
- import java.io.Serializable;
- import java.util.Map;
-
- import org.apache.commons.collections.Factory;
- import org.apache.commons.collections.Transformer;
- import org.apache.commons.collections.functors.FactoryTransformer;
-
- /**
- * Decorates another <code>Map</code> to create objects in the map on demand.
- * <p>
- * When the {@link #get(Object)} method is called with a key that does not
- * exist in the map, the factory is used to create the object. The created
- * object will be added to the map using the requested key.
- * <p>
- * For instance:
- * <pre>
- * Factory factory = new Factory() {
- * public Object create() {
- * return new Date();
- * }
- * }
- * Map lazy = Lazy.map(new HashMap(), factory);
- * Object obj = lazy.get("NOW");
- * </pre>
- *
- * After the above code is executed, <code>obj</code> will contain
- * a new <code>Date</code> instance. Furthermore, that <code>Date</code>
- * instance is mapped to the "NOW" key in the map.
- * <p>
- * This class is Serializable from Commons Collections 3.1.
- *
- * @since Commons Collections 3.0
- * @version $Revision: 1.7 $ $Date: 2004/05/07 23:30:33 $
- *
- * @author Stephen Colebourne
- * @author Paul Jack
- */
- public class LazyMap
- extends AbstractMapDecorator
- implements Map, Serializable {
-
- /** Serialization version */
- private static final long serialVersionUID = 7990956402564206740L;
-
- /** The factory to use to construct elements */
- protected final Transformer factory;
-
- /**
- * Factory method to create a lazily instantiated map.
- *
- * @param map the map to decorate, must not be null
- * @param factory the factory to use, must not be null
- * @throws IllegalArgumentException if map or factory is null
- */
- public static Map decorate(Map map, Factory factory) {
- return new LazyMap(map, factory);
- }
-
- /**
- * Factory method to create a lazily instantiated map.
- *
- * @param map the map to decorate, must not be null
- * @param factory the factory to use, must not be null
- * @throws IllegalArgumentException if map or factory is null
- */
- public static Map decorate(Map map, Transformer factory) {
- return new LazyMap(map, factory);
- }
-
- //-----------------------------------------------------------------------
- /**
- * Constructor that wraps (not copies).
- *
- * @param map the map to decorate, must not be null
- * @param factory the factory to use, must not be null
- * @throws IllegalArgumentException if map or factory is null
- */
- protected LazyMap(Map map, Factory factory) {
- super(map);
- if (factory == null) {
- throw new IllegalArgumentException("Factory must not be null");
- }
- this.factory = FactoryTransformer.getInstance(factory);
- }
-
- /**
- * Constructor that wraps (not copies).
- *
- * @param map the map to decorate, must not be null
- * @param factory the factory to use, must not be null
- * @throws IllegalArgumentException if map or factory is null
- */
- protected LazyMap(Map map, Transformer factory) {
- super(map);
- if (factory == null) {
- throw new IllegalArgumentException("Factory must not be null");
- }
- this.factory = factory;
- }
-
- //-----------------------------------------------------------------------
- /**
- * Write the map out using a custom routine.
- *
- * @param out the output stream
- * @throws IOException
- * @since Commons Collections 3.1
- */
- private void writeObject(ObjectOutputStream out) throws IOException {
- out.defaultWriteObject();
- out.writeObject(map);
- }
-
- /**
- * Read the map in using a custom routine.
- *
- * @param in the input stream
- * @throws IOException
- * @throws ClassNotFoundException
- * @since Commons Collections 3.1
- */
- private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
- in.defaultReadObject();
- map = (Map) in.readObject();
- }
-
- //-----------------------------------------------------------------------
- public Object get(Object key) {
- // create value for key if key is not currently in the map
- if (map.containsKey(key) == false) {
- Object value = factory.transform(key);
- map.put(key, value);
- return value;
- }
- return map.get(key);
- }
-
- // no need to wrap keySet, entrySet or values as they are views of
- // existing map entries - you can't do a map-style get on them.
- }