TransformedMap.java
/*
* 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.Map;
import org.apache.commons.collections4.Transformer;
/**
* Decorates another {@code Map} to transform objects that are added.
* <p>
* The Map put methods and Map.Entry setValue method are affected by this class.
* Thus objects must be removed or searched for using their transformed form.
* For example, if the transformation converts Strings to Integers, you must
* use the Integer form to remove objects.
* </p>
* <p>
* <strong>Note that TransformedMap is not synchronized and is not thread-safe.</strong>
* 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.
* </p>
* <p>
* This class is Serializable from Commons Collections 3.1.
* </p>
*
* @param <K> the type of the keys in this map
* @param <V> the type of the values in this map
* @see org.apache.commons.collections4.splitmap.TransformedSplitMap
* @since 3.0
*/
public class TransformedMap<K, V>
extends AbstractInputCheckedMapDecorator<K, V>
implements Serializable {
/** Serialization version */
private static final long serialVersionUID = 7023152376788900464L;
/**
* Factory method to create a transforming map that will transform
* existing contents of the specified map.
* <p>
* If there are any elements already in the map being decorated, they
* will be transformed by this method.
* Contrast this with {@link #transformingMap(Map, Transformer, Transformer)}.
* </p>
*
* @param <K> the key type
* @param <V> the value type
* @param map the map to decorate, must not be null
* @param keyTransformer the transformer to use for key conversion, null means no transformation
* @param valueTransformer the transformer to use for value conversion, null means no transformation
* @return a new transformed map
* @throws NullPointerException if map is null
* @since 4.0
*/
public static <K, V> TransformedMap<K, V> transformedMap(final Map<K, V> map,
final Transformer<? super K, ? extends K> keyTransformer,
final Transformer<? super V, ? extends V> valueTransformer) {
final TransformedMap<K, V> decorated = new TransformedMap<>(map, keyTransformer, valueTransformer);
if (!map.isEmpty()) {
final Map<K, V> transformed = decorated.transformMap(map);
decorated.clear();
decorated.decorated().putAll(transformed); // avoids double transformation
}
return decorated;
}
/**
* Factory method to create a transforming map.
* <p>
* If there are any elements already in the map being decorated, they
* are NOT transformed.
* Contrast this with {@link #transformedMap(Map, Transformer, Transformer)}.
* </p>
*
* @param <K> the key type
* @param <V> the value type
* @param map the map to decorate, must not be null
* @param keyTransformer the transformer to use for key conversion, null means no transformation
* @param valueTransformer the transformer to use for value conversion, null means no transformation
* @return a new transformed map
* @throws NullPointerException if map is null
* @since 4.0
*/
public static <K, V> TransformedMap<K, V> transformingMap(final Map<K, V> map,
final Transformer<? super K, ? extends K> keyTransformer,
final Transformer<? super V, ? extends V> valueTransformer) {
return new TransformedMap<>(map, keyTransformer, valueTransformer);
}
/** The transformer to use for the key */
protected final Transformer<? super K, ? extends K> keyTransformer;
/** The transformer to use for the value */
protected final Transformer<? super V, ? extends V> valueTransformer;
/**
* Constructor that wraps (not copies).
* <p>
* If there are any elements already in the collection being decorated, they
* are NOT transformed.
* </p>
*
* @param map the map to decorate, must not be null
* @param keyTransformer the transformer to use for key conversion, null means no conversion
* @param valueTransformer the transformer to use for value conversion, null means no conversion
* @throws NullPointerException if map is null
*/
protected TransformedMap(final Map<K, V> map, final Transformer<? super K, ? extends K> keyTransformer,
final Transformer<? super V, ? extends V> valueTransformer) {
super(map);
this.keyTransformer = keyTransformer;
this.valueTransformer = valueTransformer;
}
/**
* Override to transform the value when using {@code setValue}.
*
* @param value the value to transform
* @return the transformed value
* @since 3.1
*/
@Override
protected V checkSetValue(final V value) {
return valueTransformer.apply(value);
}
/**
* Override to only return true when there is a value transformer.
*
* @return true if a value transformer is in use
* @since 3.1
*/
@Override
protected boolean isSetValueChecking() {
return valueTransformer != null;
}
@Override
public V put(K key, V value) {
key = transformKey(key);
value = transformValue(value);
return decorated().put(key, value);
}
@Override
public void putAll(Map<? extends K, ? extends V> mapToCopy) {
mapToCopy = transformMap(mapToCopy);
decorated().putAll(mapToCopy);
}
/**
* Deserializes the map in using a custom routine.
*
* @param in the input stream
* @throws IOException if an error occurs while reading from the stream
* @throws ClassNotFoundException if an object read from the stream cannot be loaded
* @since 3.1
*/
@SuppressWarnings("unchecked") // (1) should only fail if input stream is incorrect
private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
in.defaultReadObject();
map = (Map<K, V>) in.readObject(); // (1)
}
/**
* Transforms a key.
* <p>
* The transformer itself may throw an exception if necessary.
*
* @param object the object to transform
* @return the transformed object
*/
protected K transformKey(final K object) {
if (keyTransformer == null) {
return object;
}
return keyTransformer.apply(object);
}
/**
* Transforms a map.
* <p>
* The transformer itself may throw an exception if necessary.
* </p>
*
* @param map the map to transform
* @return the transformed object
*/
@SuppressWarnings("unchecked")
protected Map<K, V> transformMap(final Map<? extends K, ? extends V> map) {
if (map.isEmpty()) {
return (Map<K, V>) map;
}
final Map<K, V> result = new LinkedMap<>(map.size());
for (final Map.Entry<? extends K, ? extends V> entry : map.entrySet()) {
result.put(transformKey(entry.getKey()), transformValue(entry.getValue()));
}
return result;
}
/**
* Transforms a value.
* <p>
* The transformer itself may throw an exception if necessary.
* </p>
*
* @param object the object to transform
* @return the transformed object
*/
protected V transformValue(final V object) {
if (valueTransformer == null) {
return object;
}
return valueTransformer.apply(object);
}
/**
* Serializes this object to an ObjectOutputStream.
*
* @param out the target ObjectOutputStream.
* @throws IOException thrown when an I/O errors occur writing to the target stream.
* @since 3.1
*/
private void writeObject(final ObjectOutputStream out) throws IOException {
out.defaultWriteObject();
out.writeObject(map);
}
}