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