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 */
017
018package org.apache.commons.configuration2;
019
020import org.apache.commons.configuration2.ex.ConfigurationException;
021import org.apache.commons.configuration2.io.ConfigurationLogger;
022import org.apache.commons.configuration2.tree.ImmutableNode;
023
024import java.util.ArrayList;
025import java.util.Collection;
026import java.util.Collections;
027import java.util.HashMap;
028import java.util.List;
029import java.util.Map;
030
031/**
032 * <p>
033 * A base class for configuration implementations based on YAML structures.
034 * </p>
035 * <p>
036 * This base class offers functionality related to YAML-like data structures
037 * based on maps. Such a map has strings as keys and arbitrary objects as
038 * values. The class offers methods to transform such a map into a hierarchy
039 * of {@link ImmutableNode} objects and vice versa.
040 * </p>
041 *
042 * @since 2.2
043 */
044public class AbstractYAMLBasedConfiguration extends BaseHierarchicalConfiguration
045{
046    /**
047     * Creates a new instance of {@code AbstractYAMLBasedConfiguration}.
048     */
049    protected AbstractYAMLBasedConfiguration()
050    {
051        initLogger(new ConfigurationLogger(getClass()));
052    }
053
054    /**
055     * Creates a new instance of {@code AbstractYAMLBasedConfiguration} as a
056     * copy of the specified configuration.
057     *
058     * @param c the configuration to be copied
059     */
060    protected AbstractYAMLBasedConfiguration(
061            final HierarchicalConfiguration<ImmutableNode> c)
062    {
063        super(c);
064        initLogger(new ConfigurationLogger(getClass()));
065    }
066
067    /**
068     * Loads this configuration from the content of the specified map. The data
069     * in the map is transformed into a hierarchy of {@link ImmutableNode}
070     * objects.
071     *
072     * @param map the map to be processed
073     */
074    protected void load(final Map<String, Object> map)
075    {
076        final List<ImmutableNode> roots = constructHierarchy("", map);
077        getNodeModel().setRootNode(roots.get(0));
078    }
079
080    /**
081     * Constructs a YAML map, i.e. String -&gt; Object from a given configuration
082     * node.
083     *
084     * @param node The configuration node to create a map from.
085     * @return A Map that contains the configuration node information.
086     */
087    protected Map<String, Object> constructMap(final ImmutableNode node)
088    {
089        final Map<String, Object> map = new HashMap<>(node.getChildren().size());
090        for (final ImmutableNode cNode : node.getChildren())
091        {
092            final Object value = cNode.getChildren().isEmpty() ? cNode.getValue()
093                    : constructMap(cNode);
094            addEntry(map, cNode.getNodeName(), value);
095        }
096        return map;
097    }
098
099    /**
100     * Adds a key value pair to a map, taking list structures into account. If a
101     * key is added which is already present in the map, this method ensures
102     * that a list is created.
103     *
104     * @param map the map
105     * @param key the key
106     * @param value the value
107     */
108    private static void addEntry(final Map<String, Object> map, final String key,
109            final Object value)
110    {
111        final Object oldValue = map.get(key);
112        if (oldValue == null)
113        {
114            map.put(key, value);
115        }
116        else if (oldValue instanceof Collection)
117        {
118            // safe case because the collection was created by ourselves
119            @SuppressWarnings("unchecked")
120            final
121            Collection<Object> values = (Collection<Object>) oldValue;
122            values.add(value);
123        }
124        else
125        {
126            final Collection<Object> values = new ArrayList<>();
127            values.add(oldValue);
128            values.add(value);
129            map.put(key, values);
130        }
131    }
132
133    /**
134     * Creates a part of the hierarchical nodes structure of the resulting
135     * configuration. The passed in element is converted into one or multiple
136     * configuration nodes. (If list structures are involved, multiple nodes are
137     * returned.)
138     *
139     * @param key the key of the new node(s)
140     * @param elem the element to be processed
141     * @return a list with configuration nodes representing the element
142     */
143    private static List<ImmutableNode> constructHierarchy(final String key,
144            final Object elem)
145    {
146        if (elem instanceof Map)
147        {
148            return parseMap((Map<String, Object>) elem, key);
149        }
150        else if (elem instanceof Collection)
151        {
152            return parseCollection((Collection<Object>) elem, key);
153        }
154        else
155        {
156            return Collections.singletonList(
157                    new ImmutableNode.Builder().name(key).value(elem).create());
158        }
159    }
160
161    /**
162     * Parses a map structure. The single keys of the map are processed
163     * recursively.
164     *
165     * @param map the map to be processed
166     * @param key the key under which this map is to be stored
167     * @return a node representing this map
168     */
169    private static List<ImmutableNode> parseMap(final Map<String, Object> map, final String key)
170    {
171        final ImmutableNode.Builder subtree = new ImmutableNode.Builder().name(key);
172        for (final Map.Entry<String, Object> entry : map.entrySet())
173        {
174            final List<ImmutableNode> children =
175                    constructHierarchy(entry.getKey(), entry.getValue());
176            for (final ImmutableNode child : children)
177            {
178                subtree.addChild(child);
179            }
180        }
181        return Collections.singletonList(subtree.create());
182    }
183
184    /**
185     * Parses a collection structure. The elements of the collection are
186     * processed recursively.
187     *
188     * @param col the collection to be processed
189     * @param key the key under which this collection is to be stored
190     * @return a node representing this collection
191     */
192    private static List<ImmutableNode> parseCollection(final Collection<Object> col, final String key)
193    {
194        final List<ImmutableNode> nodes = new ArrayList<>(col.size());
195        for (final Object elem : col)
196        {
197            nodes.addAll(constructHierarchy(key, elem));
198        }
199        return nodes;
200    }
201
202    /**
203     * Internal helper method to wrap an exception in a
204     * {@code ConfigurationException}.
205     * @param e the exception to be wrapped
206     * @throws ConfigurationException the resulting exception
207     */
208    static void rethrowException(final Exception e) throws ConfigurationException
209    {
210        if (e instanceof ClassCastException)
211        {
212            throw new ConfigurationException("Error parsing", e);
213        }
214        throw new ConfigurationException("Unable to load the configuration",
215                e);
216    }
217}