    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.collections4.map;
    018
    019import java.io.IOException;
    020import java.io.ObjectInputStream;
    021import java.io.ObjectOutputStream;
    022import java.io.Serializable;
    023import java.util.Map;
    024
    025import org.apache.commons.collections4.Transformer;
    026
    027/**
    028 * Decorates another <code>Map</code> to transform objects that are added.
    029 * <p>
    030 * The Map put methods and Map.Entry setValue method are affected by this class.
    031 * Thus objects must be removed or searched for using their transformed form.
    032 * For example, if the transformation converts Strings to Integers, you must
    033 * use the Integer form to remove objects.
    034 * <p>
    035 * <strong>Note that TransformedMap is not synchronized and is not thread-safe.</strong>
    036 * If you wish to use this map from multiple threads concurrently, you must use
    037 * appropriate synchronization. The simplest approach is to wrap this map
    038 * using {@link java.util.Collections#synchronizedMap(Map)}. This class may throw
    039 * exceptions when accessed by concurrent threads without synchronization.
    040 * <p>
    041 * This class is Serializable from Commons Collections 3.1.
    042 * <p>
    043 *
    044 * @param <K> the type of the keys in this map
    045 * @param <V> the type of the values in this map
    046 *
    047 * @see org.apache.commons.collections4.splitmap.TransformedSplitMap
    048 * @since 3.0
    049 */
    050public class TransformedMap<K, V>
    051        extends AbstractInputCheckedMapDecorator<K, V>
    052        implements Serializable {
    053
    054    /** Serialization version */
    055    private static final long serialVersionUID = 7023152376788900464L;
    056
    057    /** The transformer to use for the key */
    058    protected final Transformer<? super K, ? extends K> keyTransformer;
    059    /** The transformer to use for the value */
    060    protected final Transformer<? super V, ? extends V> valueTransformer;
    061
    062    /**
    063     * Factory method to create a transforming map.
    064     * <p>
    065     * If there are any elements already in the map being decorated, they
    066     * are NOT transformed.
    067     * Contrast this with {@link #transformedMap(Map, Transformer, Transformer)}.
    068     *
    069     * @param <K>  the key type
    070     * @param <V>  the value type
    071     * @param map  the map to decorate, must not be null
    072     * @param keyTransformer  the transformer to use for key conversion, null means no transformation
    073     * @param valueTransformer  the transformer to use for value conversion, null means no transformation
    074     * @return a new transformed map
    075     * @throws NullPointerException if map is null
    076     * @since 4.0
    077     */
    078    public static <K, V> TransformedMap<K, V> transformingMap(final Map<K, V> map,
    079            final Transformer<? super K, ? extends K> keyTransformer,
    080            final Transformer<? super V, ? extends V> valueTransformer) {
    081        return new TransformedMap<>(map, keyTransformer, valueTransformer);
    082    }
    083
    084    /**
    085     * Factory method to create a transforming map that will transform
    086     * existing contents of the specified map.
    087     * <p>
    088     * If there are any elements already in the map being decorated, they
    089     * will be transformed by this method.
    090     * Contrast this with {@link #transformingMap(Map, Transformer, Transformer)}.
    091     *
    092     * @param <K>  the key type
    093     * @param <V>  the value type
    094     * @param map  the map to decorate, must not be null
    095     * @param keyTransformer  the transformer to use for key conversion, null means no transformation
    096     * @param valueTransformer  the transformer to use for value conversion, null means no transformation
    097     * @return a new transformed map
    098     * @throws NullPointerException if map is null
    099     * @since 4.0
    100     */
    101    public static <K, V> TransformedMap<K, V> transformedMap(final Map<K, V> map,
    102            final Transformer<? super K, ? extends K> keyTransformer,
    103            final Transformer<? super V, ? extends V> valueTransformer) {
    104        final TransformedMap<K, V> decorated = new TransformedMap<>(map, keyTransformer, valueTransformer);
    105        if (map.size() > 0) {
    106            final Map<K, V> transformed = decorated.transformMap(map);
    107            decorated.clear();
    108            decorated.decorated().putAll(transformed);  // avoids double transformation
    109        }
    110        return decorated;
    111    }
    112
    113    //-----------------------------------------------------------------------
    114    /**
    115     * Constructor that wraps (not copies).
    116     * <p>
    117     * If there are any elements already in the collection being decorated, they
    118     * are NOT transformed.
    119     *
    120     * @param map  the map to decorate, must not be null
    121     * @param keyTransformer  the transformer to use for key conversion, null means no conversion
    122     * @param valueTransformer  the transformer to use for value conversion, null means no conversion
    123     * @throws NullPointerException if map is null
    124     */
    125    protected TransformedMap(final Map<K, V> map, final Transformer<? super K, ? extends K> keyTransformer,
    126            final Transformer<? super V, ? extends V> valueTransformer) {
    127        super(map);
    128        this.keyTransformer = keyTransformer;
    129        this.valueTransformer = valueTransformer;
    130    }
    131
    132    //-----------------------------------------------------------------------
    133    /**
    134     * Write the map out using a custom routine.
    135     *
    136     * @param out  the output stream
    137     * @throws IOException if an error occurs while writing to the stream
    138     * @since 3.1
    139     */
    140    private void writeObject(final ObjectOutputStream out) throws IOException {
    141        out.defaultWriteObject();
    142        out.writeObject(map);
    143    }
    144
    145    /**
    146     * Read the map in using a custom routine.
    147     *
    148     * @param in  the input stream
    149     * @throws IOException if an error occurs while reading from the stream
    150     * @throws ClassNotFoundException if an object read from the stream can not be loaded
    151     * @since 3.1
    152     */
    153    @SuppressWarnings("unchecked") // (1) should only fail if input stream is incorrect
    154    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
    155        in.defaultReadObject();
    156        map = (Map<K, V>) in.readObject(); // (1)
    157    }
    158
    159    //-----------------------------------------------------------------------
    160    /**
    161     * Transforms a key.
    162     * <p>
    163     * The transformer itself may throw an exception if necessary.
    164     *
    165     * @param object  the object to transform
    166     * @return the transformed object
    167     */
    168    protected K transformKey(final K object) {
    169        if (keyTransformer == null) {
    170            return object;
    171        }
    172        return keyTransformer.transform(object);
    173    }
    174
    175    /**
    176     * Transforms a value.
    177     * <p>
    178     * The transformer itself may throw an exception if necessary.
    179     *
    180     * @param object  the object to transform
    181     * @return the transformed object
    182     */
    183    protected V transformValue(final V object) {
    184        if (valueTransformer == null) {
    185            return object;
    186        }
    187        return valueTransformer.transform(object);
    188    }
    189
    190    /**
    191     * Transforms a map.
    192     * <p>
    193     * The transformer itself may throw an exception if necessary.
    194     *
    195     * @param map  the map to transform
    196     * @return the transformed object
    197     */
    198    @SuppressWarnings("unchecked")
    199    protected Map<K, V> transformMap(final Map<? extends K, ? extends V> map) {
    200        if (map.isEmpty()) {
    201            return (Map<K, V>) map;
    202        }
    203        final Map<K, V> result = new LinkedMap<>(map.size());
    204
    205        for (final Map.Entry<? extends K, ? extends V> entry : map.entrySet()) {
    206            result.put(transformKey(entry.getKey()), transformValue(entry.getValue()));
    207        }
    208        return result;
    209    }
    210
    211    /**
    212     * Override to transform the value when using <code>setValue</code>.
    213     *
    214     * @param value  the value to transform
    215     * @return the transformed value
    216     * @since 3.1
    217     */
    218    @Override
    219    protected V checkSetValue(final V value) {
    220        return valueTransformer.transform(value);
    221    }
    222
    223    /**
    224     * Override to only return true when there is a value transformer.
    225     *
    226     * @return true if a value transformer is in use
    227     * @since 3.1
    228     */
    229    @Override
    230    protected boolean isSetValueChecking() {
    231        return valueTransformer != null;
    232    }
    233
    234    //-----------------------------------------------------------------------
    235    @Override
    236    public V put(K key, V value) {
    237        key = transformKey(key);
    238        value = transformValue(value);
    239        return decorated().put(key, value);
    240    }
    241
    242    @Override
    243    public void putAll(Map<? extends K, ? extends V> mapToCopy) {
    244        mapToCopy = transformMap(mapToCopy);
    245        decorated().putAll(mapToCopy);
    246    }
    247
    248}