    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} 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 * <p>
    036 * <strong>Note that TransformedMap is not synchronized and is not thread-safe.</strong>
    037 * If you wish to use this map from multiple threads concurrently, you must use
    038 * appropriate synchronization. The simplest approach is to wrap this map
    039 * using {@link java.util.Collections#synchronizedMap(Map)}. This class may throw
    040 * exceptions when accessed by concurrent threads without synchronization.
    041 * </p>
    042 * <p>
    043 * This class is Serializable from Commons Collections 3.1.
    044 * </p>
    045 *
    046 * @param <K> the type of the keys in this map
    047 * @param <V> the type of the values in this map
    048 * @see org.apache.commons.collections4.splitmap.TransformedSplitMap
    049 * @since 3.0
    050 */
    051public class TransformedMap<K, V>
    052        extends AbstractInputCheckedMapDecorator<K, V>
    053        implements Serializable {
    054
    055    /** Serialization version */
    056    private static final long serialVersionUID = 7023152376788900464L;
    057
    058    /**
    059     * Factory method to create a transforming map that will transform
    060     * existing contents of the specified map.
    061     * <p>
    062     * If there are any elements already in the map being decorated, they
    063     * will be transformed by this method.
    064     * Contrast this with {@link #transformingMap(Map, Transformer, Transformer)}.
    065     * </p>
    066     *
    067     * @param <K>  the key type
    068     * @param <V>  the value type
    069     * @param map  the map to decorate, must not be null
    070     * @param keyTransformer  the transformer to use for key conversion, null means no transformation
    071     * @param valueTransformer  the transformer to use for value conversion, null means no transformation
    072     * @return a new transformed map
    073     * @throws NullPointerException if map is null
    074     * @since 4.0
    075     */
    076    public static <K, V> TransformedMap<K, V> transformedMap(final Map<K, V> map,
    077            final Transformer<? super K, ? extends K> keyTransformer,
    078            final Transformer<? super V, ? extends V> valueTransformer) {
    079        final TransformedMap<K, V> decorated = new TransformedMap<>(map, keyTransformer, valueTransformer);
    080        if (!map.isEmpty()) {
    081            final Map<K, V> transformed = decorated.transformMap(map);
    082            decorated.clear();
    083            decorated.decorated().putAll(transformed);  // avoids double transformation
    084        }
    085        return decorated;
    086    }
    087    /**
    088     * Factory method to create a transforming map.
    089     * <p>
    090     * If there are any elements already in the map being decorated, they
    091     * are NOT transformed.
    092     * Contrast this with {@link #transformedMap(Map, Transformer, Transformer)}.
    093     * </p>
    094     *
    095     * @param <K>  the key type
    096     * @param <V>  the value type
    097     * @param map  the map to decorate, must not be null
    098     * @param keyTransformer  the transformer to use for key conversion, null means no transformation
    099     * @param valueTransformer  the transformer to use for value conversion, null means no transformation
    100     * @return a new transformed map
    101     * @throws NullPointerException if map is null
    102     * @since 4.0
    103     */
    104    public static <K, V> TransformedMap<K, V> transformingMap(final Map<K, V> map,
    105            final Transformer<? super K, ? extends K> keyTransformer,
    106            final Transformer<? super V, ? extends V> valueTransformer) {
    107        return new TransformedMap<>(map, keyTransformer, valueTransformer);
    108    }
    109
    110    /** The transformer to use for the key */
    111    protected final Transformer<? super K, ? extends K> keyTransformer;
    112
    113    /** The transformer to use for the value */
    114    protected final Transformer<? super V, ? extends V> valueTransformer;
    115
    116    /**
    117     * Constructor that wraps (not copies).
    118     * <p>
    119     * If there are any elements already in the collection being decorated, they
    120     * are NOT transformed.
    121     * </p>
    122     *
    123     * @param map  the map to decorate, must not be null
    124     * @param keyTransformer  the transformer to use for key conversion, null means no conversion
    125     * @param valueTransformer  the transformer to use for value conversion, null means no conversion
    126     * @throws NullPointerException if map is null
    127     */
    128    protected TransformedMap(final Map<K, V> map, final Transformer<? super K, ? extends K> keyTransformer,
    129            final Transformer<? super V, ? extends V> valueTransformer) {
    130        super(map);
    131        this.keyTransformer = keyTransformer;
    132        this.valueTransformer = valueTransformer;
    133    }
    134
    135    /**
    136     * Override to transform the value when using {@code setValue}.
    137     *
    138     * @param value  the value to transform
    139     * @return the transformed value
    140     * @since 3.1
    141     */
    142    @Override
    143    protected V checkSetValue(final V value) {
    144        return valueTransformer.apply(value);
    145    }
    146
    147    /**
    148     * Override to only return true when there is a value transformer.
    149     *
    150     * @return true if a value transformer is in use
    151     * @since 3.1
    152     */
    153    @Override
    154    protected boolean isSetValueChecking() {
    155        return valueTransformer != null;
    156    }
    157
    158    @Override
    159    public V put(K key, V value) {
    160        key = transformKey(key);
    161        value = transformValue(value);
    162        return decorated().put(key, value);
    163    }
    164
    165    @Override
    166    public void putAll(Map<? extends K, ? extends V> mapToCopy) {
    167        mapToCopy = transformMap(mapToCopy);
    168        decorated().putAll(mapToCopy);
    169    }
    170
    171    /**
    172     * Deserializes the map in using a custom routine.
    173     *
    174     * @param in  the input stream
    175     * @throws IOException if an error occurs while reading from the stream
    176     * @throws ClassNotFoundException if an object read from the stream cannot be loaded
    177     * @since 3.1
    178     */
    179    @SuppressWarnings("unchecked") // (1) should only fail if input stream is incorrect
    180    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
    181        in.defaultReadObject();
    182        map = (Map<K, V>) in.readObject(); // (1)
    183    }
    184
    185    /**
    186     * Transforms a key.
    187     * <p>
    188     * The transformer itself may throw an exception if necessary.
    189     *
    190     * @param object  the object to transform
    191     * @return the transformed object
    192     */
    193    protected K transformKey(final K object) {
    194        if (keyTransformer == null) {
    195            return object;
    196        }
    197        return keyTransformer.apply(object);
    198    }
    199
    200    /**
    201     * Transforms a map.
    202     * <p>
    203     * The transformer itself may throw an exception if necessary.
    204     * </p>
    205     *
    206     * @param map  the map to transform
    207     * @return the transformed object
    208     */
    209    @SuppressWarnings("unchecked")
    210    protected Map<K, V> transformMap(final Map<? extends K, ? extends V> map) {
    211        if (map.isEmpty()) {
    212            return (Map<K, V>) map;
    213        }
    214        final Map<K, V> result = new LinkedMap<>(map.size());
    215
    216        for (final Map.Entry<? extends K, ? extends V> entry : map.entrySet()) {
    217            result.put(transformKey(entry.getKey()), transformValue(entry.getValue()));
    218        }
    219        return result;
    220    }
    221
    222    /**
    223     * Transforms a value.
    224     * <p>
    225     * The transformer itself may throw an exception if necessary.
    226     * </p>
    227     *
    228     * @param object  the object to transform
    229     * @return the transformed object
    230     */
    231    protected V transformValue(final V object) {
    232        if (valueTransformer == null) {
    233            return object;
    234        }
    235        return valueTransformer.apply(object);
    236    }
    237
    238    /**
    239     * Serializes this object to an ObjectOutputStream.
    240     *
    241     * @param out the target ObjectOutputStream.
    242     * @throws IOException thrown when an I/O errors occur writing to the target stream.
    243     * @since 3.1
    244     */
    245    private void writeObject(final ObjectOutputStream out) throws IOException {
    246        out.defaultWriteObject();
    247        out.writeObject(map);
    248    }
    249
    250}