    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}