    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}