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