org.apache.commons.collections.map.DefaultedMap Maven / Gradle / Ivy
/*
* 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.collections.map;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;
import org.apache.commons.collections.Factory;
import org.apache.commons.collections.Transformer;
import org.apache.commons.collections.functors.ConstantTransformer;
import org.apache.commons.collections.functors.FactoryTransformer;
/**
* Decorates another Map returning a default value if the map
* does not contain the requested key.
*
* When the {@link #get(Object)} method is called with a key that does not
* exist in the map, this map will return the default value specified in
* the constructor/factory. Only the get method is altered, so the
* {@link Map#containsKey(Object)} can be used to determine if a key really
* is in the map or not.
*
* The defaulted value is not added to the map.
* Compare this behaviour with {@link LazyMap}, which does add the value
* to the map (via a Transformer).
*
* For instance:
*
* Map map = new DefaultedMap("NULL");
* Object obj = map.get("Surname");
* // obj == "NULL"
*
* After the above code is executed the map is still empty.
*
* Note that DefaultedMap is not synchronized and is not thread-safe.
* 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.
*
* @since Commons Collections 3.2
* @version $Revision: 1.7 $ $Date$
*
* @author Stephen Colebourne
* @author Rafael U.C. Afonso
* @see LazyMap
*
* @deprecated Apache Commons Collections version 3.x is being deprecated from AEMaaCS. The upgraded version 4.4 of Commons Collections is already included as replacement. Customers are advised to upgrade to this version of the library. Please note: the package name was changed to org.apache.commons.collections4. Further note that there are AEM APIs currently exposing the old collections classes; these will be updated in upcoming releases.
*/
// no need to wrap keySet, entrySet or values as they are views of
// existing map entries - you can't do a map-style get on them.
@Deprecated(since = "2021-04-30")
public class DefaultedMap extends AbstractMapDecorator implements Map, Serializable {
/**
* Serialization version
*/
private static final long serialVersionUID = 19698628745827L;
/**
* The transformer to use if the map does not contain a key
*/
protected final Object value;
// -----------------------------------------------------------------------
/**
* Factory method to create a defaulting map.
*
* The value specified is returned when a missing key is found.
*
* @param map the map to decorate, must not be null
* @param defaultValue the default value to return when the key is not found
* @throws IllegalArgumentException if map is null
*/
public static Map decorate(Map map, Object defaultValue) {
if (defaultValue instanceof Transformer) {
defaultValue = ConstantTransformer.getInstance(defaultValue);
}
return new DefaultedMap(map, defaultValue);
}
/**
* Factory method to create a defaulting map.
*
* The factory specified is called when a missing key is found.
* The result will be returned as the result of the map get(key) method.
*
* @param map the map to decorate, must not be null
* @param factory the factory to use, must not be null
* @throws IllegalArgumentException if map or factory is null
*/
public static Map decorate(Map map, Factory factory) {
if (factory == null) {
throw new IllegalArgumentException("Factory must not be null");
}
return new DefaultedMap(map, FactoryTransformer.getInstance(factory));
}
/**
* Factory method to create a defaulting map.
*
* The transformer specified is called when a missing key is found.
* The key is passed to the transformer as the input, and the result
* will be returned as the result of the map get(key) method.
*
* @param map the map to decorate, must not be null
* @param factory the factory to use, must not be null
* @throws IllegalArgumentException if map or factory is null
*/
public static Map decorate(Map map, Transformer factory) {
if (factory == null) {
throw new IllegalArgumentException("Transformer must not be null");
}
return new DefaultedMap(map, factory);
}
// -----------------------------------------------------------------------
/**
* Constructs a new empty DefaultedMap that decorates
* a HashMap.
*
* The object passed in will be returned by the map whenever an
* unknown key is requested.
*
* @param defaultValue the default value to return when the key is not found
*/
public DefaultedMap(Object defaultValue) {
super(new HashMap());
if (defaultValue instanceof Transformer) {
defaultValue = ConstantTransformer.getInstance(defaultValue);
}
this.value = defaultValue;
}
/**
* Constructor that wraps (not copies).
*
* @param map the map to decorate, must not be null
* @param value the value to use
* @throws IllegalArgumentException if map or transformer is null
*/
protected DefaultedMap(Map map, Object value) {
super(map);
this.value = value;
}
// -----------------------------------------------------------------------
/**
* Write the map out using a custom routine.
*
* @param out the output stream
* @throws IOException
*/
private void writeObject(ObjectOutputStream out) throws IOException {
out.defaultWriteObject();
out.writeObject(map);
}
/**
* Read the map in using a custom routine.
*
* @param in the input stream
* @throws IOException
* @throws ClassNotFoundException
*/
private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
in.defaultReadObject();
map = (Map) in.readObject();
}
// -----------------------------------------------------------------------
public Object get(Object key) {
// create value for key if key is not currently in the map
if (map.containsKey(key) == false) {
if (value instanceof Transformer) {
return ((Transformer) value).transform(key);
}
return value;
}
return map.get(key);
}
// no need to wrap keySet, entrySet or values as they are views of
// existing map entries - you can't do a map-style get on them.
}