| /* |
| * 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> |
| * <strong>Note that LazyMap is not synchronized and is not thread-safe.</strong> |
| * If you wish to use this map from multiple threads concurrently, you must use |
| * appropriate synchronization. The simplest approach is to wrap this map |
| * using {@link java.util.Collections#synchronizedMap(Map)}. This class may throw |
| * exceptions when accessed by concurrent threads without synchronization. |
| * <p> |
| * This class is Serializable from Commons Collections 3.1. |
| * |
| * @since Commons Collections 3.0 |
| * @version $Revision: 1.1 $ $Date: 2009/05/27 22:16:29 $ |
| * |
| * @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. |
| } |