    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 *
    049 * @see org.apache.commons.collections4.splitmap.TransformedSplitMap
    050 * @since 3.0
    051 */
    052public class TransformedMap<K, V>
    053        extends AbstractInputCheckedMapDecorator<K, V>
    054        implements Serializable {
    055
    056    /** Serialization version */
    057    private static final long serialVersionUID = 7023152376788900464L;
    058
    059    /**
    060     * Factory method to create a transforming map that will transform
    061     * existing contents of the specified map.
    062     * <p>
    063     * If there are any elements already in the map being decorated, they
    064     * will be transformed by this method.
    065     * Contrast this with {@link #transformingMap(Map, Transformer, Transformer)}.
    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     *
    094     * @param <K>  the key type
    095     * @param <V>  the value type
    096     * @param map  the map to decorate, must not be null
    097     * @param keyTransformer  the transformer to use for key conversion, null means no transformation
    098     * @param valueTransformer  the transformer to use for value conversion, null means no transformation
    099     * @return a new transformed map
    100     * @throws NullPointerException if map is null
    101     * @since 4.0
    102     */
    103    public static <K, V> TransformedMap<K, V> transformingMap(final Map<K, V> map,
    104            final Transformer<? super K, ? extends K> keyTransformer,
    105            final Transformer<? super V, ? extends V> valueTransformer) {
    106        return new TransformedMap<>(map, keyTransformer, valueTransformer);
    107    }
    108
    109    /** The transformer to use for the key */
    110    protected final Transformer<? super K, ? extends K> keyTransformer;
    111
    112    /** The transformer to use for the value */
    113    protected final Transformer<? super V, ? extends V> valueTransformer;
    114
    115    /**
    116     * Constructor that wraps (not copies).
    117     * <p>
    118     * If there are any elements already in the collection being decorated, they
    119     * are NOT transformed.
    120     *
    121     * @param map  the map to decorate, must not be null
    122     * @param keyTransformer  the transformer to use for key conversion, null means no conversion
    123     * @param valueTransformer  the transformer to use for value conversion, null means no conversion
    124     * @throws NullPointerException if map is null
    125     */
    126    protected TransformedMap(final Map<K, V> map, final Transformer<? super K, ? extends K> keyTransformer,
    127            final Transformer<? super V, ? extends V> valueTransformer) {
    128        super(map);
    129        this.keyTransformer = keyTransformer;
    130        this.valueTransformer = valueTransformer;
    131    }
    132
    133    /**
    134     * Override to transform the value when using {@code setValue}.
    135     *
    136     * @param value  the value to transform
    137     * @return the transformed value
    138     * @since 3.1
    139     */
    140    @Override
    141    protected V checkSetValue(final V value) {
    142        return valueTransformer.transform(value);
    143    }
    144
    145    /**
    146     * Override to only return true when there is a value transformer.
    147     *
    148     * @return true if a value transformer is in use
    149     * @since 3.1
    150     */
    151    @Override
    152    protected boolean isSetValueChecking() {
    153        return valueTransformer != null;
    154    }
    155
    156    @Override
    157    public V put(K key, V value) {
    158        key = transformKey(key);
    159        value = transformValue(value);
    160        return decorated().put(key, value);
    161    }
    162
    163    @Override
    164    public void putAll(Map<? extends K, ? extends V> mapToCopy) {
    165        mapToCopy = transformMap(mapToCopy);
    166        decorated().putAll(mapToCopy);
    167    }
    168
    169    /**
    170     * Read the map in using a custom routine.
    171     *
    172     * @param in  the input stream
    173     * @throws IOException if an error occurs while reading from the stream
    174     * @throws ClassNotFoundException if an object read from the stream can not be loaded
    175     * @since 3.1
    176     */
    177    @SuppressWarnings("unchecked") // (1) should only fail if input stream is incorrect
    178    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
    179        in.defaultReadObject();
    180        map = (Map<K, V>) in.readObject(); // (1)
    181    }
    182
    183    /**
    184     * Transforms a key.
    185     * <p>
    186     * The transformer itself may throw an exception if necessary.
    187     *
    188     * @param object  the object to transform
    189     * @return the transformed object
    190     */
    191    protected K transformKey(final K object) {
    192        if (keyTransformer == null) {
    193            return object;
    194        }
    195        return keyTransformer.transform(object);
    196    }
    197
    198    /**
    199     * Transforms a map.
    200     * <p>
    201     * The transformer itself may throw an exception if necessary.
    202     *
    203     * @param map  the map to transform
    204     * @return the transformed object
    205     */
    206    @SuppressWarnings("unchecked")
    207    protected Map<K, V> transformMap(final Map<? extends K, ? extends V> map) {
    208        if (map.isEmpty()) {
    209            return (Map<K, V>) map;
    210        }
    211        final Map<K, V> result = new LinkedMap<>(map.size());
    212
    213        for (final Map.Entry<? extends K, ? extends V> entry : map.entrySet()) {
    214            result.put(transformKey(entry.getKey()), transformValue(entry.getValue()));
    215        }
    216        return result;
    217    }
    218
    219    /**
    220     * Transforms a value.
    221     * <p>
    222     * The transformer itself may throw an exception if necessary.
    223     *
    224     * @param object  the object to transform
    225     * @return the transformed object
    226     */
    227    protected V transformValue(final V object) {
    228        if (valueTransformer == null) {
    229            return object;
    230        }
    231        return valueTransformer.transform(object);
    232    }
    233
    234    /**
    235     * Write the map out using a custom routine.
    236     *
    237     * @param out  the output stream
    238     * @throws IOException if an error occurs while writing to the stream
    239     * @since 3.1
    240     */
    241    private void writeObject(final ObjectOutputStream out) throws IOException {
    242        out.defaultWriteObject();
    243        out.writeObject(map);
    244    }
    245
    246}