    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.splitmap;
    018
    019import java.io.IOException;
    020import java.io.ObjectInputStream;
    021import java.io.ObjectOutputStream;
    022import java.io.Serializable;
    023import java.util.Map;
    024import java.util.Objects;
    025
    026import org.apache.commons.collections4.Put;
    027import org.apache.commons.collections4.Transformer;
    028import org.apache.commons.collections4.map.LinkedMap;
    029
    030/**
    031 * Decorates another {@link Map} to transform objects that are added.
    032 * <p>
    033 * The Map put methods and Map.Entry setValue method are affected by this class.
    034 * Thus objects must be removed or searched for using their transformed form.
    035 * For example, if the transformation converts Strings to Integers, you must use
    036 * the Integer form to remove objects.
    037 * </p>
    038 * <p>
    039 * <strong>Note that TransformedMap is not synchronized and is not
    040 * thread-safe.</strong> If you wish to use this map from multiple threads
    041 * concurrently, you must use appropriate synchronization. The simplest approach
    042 * is to wrap this map using {@link java.util.Collections#synchronizedMap(Map)}.
    043 * This class may throw exceptions when accessed by concurrent threads without
    044 * synchronization.
    045 * </p>
    046 * <p>
    047 * The "put" and "get" type constraints of this class are mutually independent;
    048 * contrast with {@link org.apache.commons.collections4.map.TransformedMap} which,
    049 * by virtue of its implementing {@link Map}&lt;K, V&gt;, must be constructed in such
    050 * a way that its read and write parameters are generalized to a common (super-)type.
    051 * In practice this would often mean {@code &gt;Object, Object&gt;}, defeating
    052 * much of the usefulness of having parameterized types.
    053 * </p>
    054 * <p>
    055 * On the downside, this class is not drop-in compatible with {@link java.util.Map}
    056 * but is intended to be worked with either directly or by {@link Put} and
    057 * {@link org.apache.commons.collections4.Get Get} generalizations.
    058 * </p>
    059 *
    060 * @param <J> the type of the keys to put in this map
    061 * @param <K> the type of the keys to get in this map
    062 * @param <U> the type of the values to put in this map
    063 * @param <V> the type of the values to get in this map
    064 * @since 4.0
    065 * @see org.apache.commons.collections4.SplitMapUtils#readableMap(org.apache.commons.collections4.Get)
    066 * @see org.apache.commons.collections4.SplitMapUtils#writableMap(Put)
    067 */
    068public class TransformedSplitMap<J, K, U, V> extends AbstractIterableGetMapDecorator<K, V>
    069        implements Put<J, U>, Serializable {
    070
    071    /** Serialization version */
    072    private static final long serialVersionUID = 5966875321133456994L;
    073
    074    /**
    075     * Factory method to create a transforming map.
    076     * <p>
    077     * If there are any elements already in the map being decorated, they are
    078     * NOT transformed.
    079     *
    080     * @param <J>  the input key type
    081     * @param <K>  the output key type
    082     * @param <U>  the input value type
    083     * @param <V>  the output value type
    084     * @param map the map to decorate, must not be null
    085     * @param keyTransformer the transformer to use for key conversion, must not be null
    086     * @param valueTransformer the transformer to use for value conversion, must not be null
    087     * @return a new transformed map
    088     * @throws NullPointerException if map or either of the transformers is null
    089     */
    090    public static <J, K, U, V> TransformedSplitMap<J, K, U, V> transformingMap(final Map<K, V> map,
    091            final Transformer<? super J, ? extends K> keyTransformer,
    092            final Transformer<? super U, ? extends V> valueTransformer) {
    093        return new TransformedSplitMap<>(map, keyTransformer, valueTransformer);
    094    }
    095    /** The transformer to use for the key */
    096    private final Transformer<? super J, ? extends K> keyTransformer;
    097
    098    /** The transformer to use for the value */
    099    private final Transformer<? super U, ? extends V> valueTransformer;
    100
    101    /**
    102     * Constructor that wraps (not copies).
    103     * <p>
    104     * If there are any elements already in the collection being decorated, they
    105     * are NOT transformed.
    106     *
    107     * @param map the map to decorate, must not be null
    108     * @param keyTransformer the transformer to use for key conversion, must not be null
    109     * @param valueTransformer the transformer to use for value conversion, must not be null
    110     * @throws NullPointerException if map or either of the transformers is null
    111     */
    112    protected TransformedSplitMap(final Map<K, V> map, final Transformer<? super J, ? extends K> keyTransformer,
    113            final Transformer<? super U, ? extends V> valueTransformer) {
    114        super(map);
    115        this.keyTransformer = Objects.requireNonNull(keyTransformer, "keyTransformer");
    116        this.valueTransformer = Objects.requireNonNull(valueTransformer, "valueTransformer");
    117    }
    118
    119    /**
    120     * Override to transform the value when using {@code setValue}.
    121     *
    122     * @param value the value to transform
    123     * @return the transformed value
    124     */
    125    protected V checkSetValue(final U value) {
    126        return valueTransformer.apply(value);
    127    }
    128
    129    @Override
    130    public void clear() {
    131        decorated().clear();
    132    }
    133
    134    @Override
    135    public V put(final J key, final U value) {
    136        return decorated().put(transformKey(key), transformValue(value));
    137    }
    138
    139    @Override
    140    public void putAll(final Map<? extends J, ? extends U> mapToCopy) {
    141        decorated().putAll(transformMap(mapToCopy));
    142    }
    143
    144    /**
    145     * Deserializes the map in using a custom routine.
    146     *
    147     * @param in the input stream
    148     * @throws IOException if an error occurs while reading from the stream
    149     * @throws ClassNotFoundException if an object read from the stream cannot be loaded
    150     * @since 3.1
    151     */
    152    @SuppressWarnings("unchecked") // (1) should only fail if input stream is incorrect
    153    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
    154        in.defaultReadObject();
    155        map = (Map<K, V>) in.readObject(); // (1)
    156    }
    157
    158    /**
    159     * Transforms a key.
    160     * <p>
    161     * The transformer itself may throw an exception if necessary.
    162     *
    163     * @param object the object to transform
    164     * @return the transformed object
    165     */
    166    protected K transformKey(final J object) {
    167        return keyTransformer.apply(object);
    168    }
    169
    170    /**
    171     * Transforms a map.
    172     * <p>
    173     * The transformer itself may throw an exception if necessary.
    174     *
    175     * @param map the map to transform
    176     * @return the transformed object
    177     */
    178    @SuppressWarnings("unchecked")
    179    protected Map<K, V> transformMap(final Map<? extends J, ? extends U> map) {
    180        if (map.isEmpty()) {
    181            return (Map<K, V>) map;
    182        }
    183        final Map<K, V> result = new LinkedMap<>(map.size());
    184
    185        for (final Map.Entry<? extends J, ? extends U> entry : map.entrySet()) {
    186            result.put(transformKey(entry.getKey()), transformValue(entry.getValue()));
    187        }
    188        return result;
    189    }
    190
    191    /**
    192     * Transforms a value.
    193     * <p>
    194     * The transformer itself may throw an exception if necessary.
    195     *
    196     * @param object the object to transform
    197     * @return the transformed object
    198     */
    199    protected V transformValue(final U object) {
    200        return valueTransformer.apply(object);
    201    }
    202
    203    /**
    204     * Serializes this object to an ObjectOutputStream.
    205     *
    206     * @param out the target ObjectOutputStream.
    207     * @throws IOException thrown when an I/O errors occur writing to the target stream.
    208     */
    209    private void writeObject(final ObjectOutputStream out) throws IOException {
    210        out.defaultWriteObject();
    211        out.writeObject(decorated());
    212    }
    213}