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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.collections4.map;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;

import org.apache.commons.collections4.Factory;
import org.apache.commons.collections4.Transformer;
import org.apache.commons.collections4.functors.ConstantTransformer;
import org.apache.commons.collections4.functors.FactoryTransformer;

/**
 * Decorates another Map returning a default value if the map
 * does not contain the requested key.
 * 

* When the {@link #get(Object)} method is called with a key that does not * exist in the map, this map will return the default value specified in * the constructor/factory. Only the get method is altered, so the * {@link Map#containsKey(Object)} can be used to determine if a key really * is in the map or not. *

* The defaulted value is not added to the map. * Compare this behaviour with {@link LazyMap}, which does add the value * to the map (via a Transformer). *

* For instance: *

 * Map map = new DefaultedMap("NULL");
 * Object obj = map.get("Surname");
 * // obj == "NULL"
 * 
* After the above code is executed the map is still empty. *

* Note that DefaultedMap is not synchronized and is not thread-safe. * 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. * * @since 3.2 * @version $Id: DefaultedMap.java 1686855 2015-06-22 13:00:27Z tn $ * * @see LazyMap */ public class DefaultedMap extends AbstractMapDecorator implements Serializable { /** Serialization version */ private static final long serialVersionUID = 19698628745827L; /** The transformer to use if the map does not contain a key */ private final Transformer value; //----------------------------------------------------------------------- /** * Factory method to create a defaulting map. *

* The value specified is returned when a missing key is found. * * @param the key type * @param the value type * @param map the map to decorate, must not be null * @param defaultValue the default value to return when the key is not found * @return a new defaulting map * @throws NullPointerException if map is null * @since 4.0 */ public static DefaultedMap defaultedMap(final Map map, final V defaultValue) { return new DefaultedMap(map, ConstantTransformer.constantTransformer(defaultValue)); } /** * Factory method to create a defaulting map. *

* The factory specified is called when a missing key is found. * The result will be returned as the result of the map get(key) method. * * @param the key type * @param the value type * @param map the map to decorate, must not be null * @param factory the factory to use to create entries, must not be null * @return a new defaulting map * @throws NullPointerException if map or factory is null * @since 4.0 */ public static DefaultedMap defaultedMap(final Map map, final Factory factory) { if (factory == null) { throw new IllegalArgumentException("Factory must not be null"); } return new DefaultedMap(map, FactoryTransformer.factoryTransformer(factory)); } /** * Factory method to create a defaulting map. *

* The transformer specified is called when a missing key is found. * The key is passed to the transformer as the input, and the result * will be returned as the result of the map get(key) method. * * @param the key type * @param the value type * @param map the map to decorate, must not be null * @param transformer the transformer to use as a factory to create entries, must not be null * @return a new defaulting map * @throws NullPointerException if map or factory is null * @since 4.0 */ public static Map defaultedMap(final Map map, final Transformer transformer) { if (transformer == null) { throw new IllegalArgumentException("Transformer must not be null"); } return new DefaultedMap(map, transformer); } //----------------------------------------------------------------------- /** * Constructs a new empty DefaultedMap that decorates * a HashMap. *

* The object passed in will be returned by the map whenever an * unknown key is requested. * * @param defaultValue the default value to return when the key is not found */ public DefaultedMap(final V defaultValue) { this(ConstantTransformer.constantTransformer(defaultValue)); } /** * Constructs a new empty DefaultedMap that decorates a HashMap. * * @param defaultValueTransformer transformer to use to generate missing values. */ public DefaultedMap(final Transformer defaultValueTransformer) { this(new HashMap(), defaultValueTransformer); } /** * Constructor that wraps (not copies). * * @param map the map to decorate, must not be null * @param defaultValueTransformer the value transformer to use * @throws NullPointerException if map or transformer is null */ protected DefaultedMap(final Map map, final Transformer defaultValueTransformer) { super(map); if (defaultValueTransformer == null) { throw new NullPointerException("Transformer must not be null."); } this.value = defaultValueTransformer; } //----------------------------------------------------------------------- /** * Write the map out using a custom routine. * * @param out the output stream * @throws IOException */ private void writeObject(final 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 */ @SuppressWarnings("unchecked") private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException { in.defaultReadObject(); map = (Map) in.readObject(); } //----------------------------------------------------------------------- @Override @SuppressWarnings("unchecked") public V get(final Object key) { // create value for key if key is not currently in the map if (map.containsKey(key) == false) { return value.transform((K) key); } 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. }





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