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