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 */
017package org.apache.commons.configuration.tree;
018
019import java.util.ArrayList;
020import java.util.Iterator;
021import java.util.LinkedList;
022import java.util.List;
023
024/**
025 * <p>
026 * A specialized implementation of the {@code NodeCombiner} interface
027 * that performs a merge from two passed in node hierarchies.
028 * </p>
029 * <p>
030 * This combiner performs the merge using a few rules:
031 * <ol>
032 * <li>Nodes can be merged when attributes that appear in both have the same value.</li>
033 * <li>Only a single node in the second file is considered a match to the node in the first file.</li>
034 * <li>Attributes in nodes that match are merged.
035 * <li>Nodes in both files that do not match are added to the result.</li>
036 * </ol>
037 * </p>
038 *
039 * @author <a
040 * href="http://commons.apache.org/configuration/team-list.html">Commons
041 * Configuration team</a>
042 * @version $Id: MergeCombiner.java 1301991 2012-03-17 20:18:02Z sebb $
043 * @since 1.7
044 */
045public class MergeCombiner extends NodeCombiner
046{
047    /**
048     * Combines the given nodes to a new union node.
049     *
050     * @param node1 the first source node
051     * @param node2 the second source node
052     * @return the union node
053     */
054
055    @Override
056    public ConfigurationNode combine(ConfigurationNode node1, ConfigurationNode node2)
057    {
058        ViewNode result = createViewNode();
059        result.setName(node1.getName());
060        result.setValue(node1.getValue());
061        addAttributes(result, node1, node2);
062
063        // Check if nodes can be combined
064        List<ConfigurationNode> children2 = new LinkedList<ConfigurationNode>(node2.getChildren());
065        for (ConfigurationNode child1 : node1.getChildren())
066        {
067            ConfigurationNode child2 = canCombine(node1, node2, child1, children2);
068            if (child2 != null)
069            {
070                result.addChild(combine(child1, child2));
071                children2.remove(child2);
072            }
073            else
074            {
075                result.addChild(child1);
076            }
077        }
078
079        // Add remaining children of node 2
080        for (ConfigurationNode c : children2)
081        {
082            result.addChild(c);
083        }
084        return result;
085    }
086
087    /**
088     * Handles the attributes during a combination process. First all attributes
089     * of the first node will be added to the result. Then all attributes of the
090     * second node, which are not contained in the first node, will also be
091     * added.
092     *
093     * @param result the resulting node
094     * @param node1 the first node
095     * @param node2 the second node
096     */
097    protected void addAttributes(ViewNode result, ConfigurationNode node1,
098            ConfigurationNode node2)
099    {
100        result.appendAttributes(node1);
101        for (ConfigurationNode attr : node2.getAttributes())
102        {
103            if (node1.getAttributeCount(attr.getName()) == 0)
104            {
105                result.addAttribute(attr);
106            }
107        }
108    }
109
110    /**
111     * Tests if the first node can be combined with the second node. A node can
112     * only be combined if its attributes are all present in the second node and
113     * they all have the same value.
114     *
115     * @param node1 the first node
116     * @param node2 the second node
117     * @param child the child node (of the first node)
118     * @return a child of the second node, with which a combination is possible
119     */
120    protected ConfigurationNode canCombine(ConfigurationNode node1,
121            ConfigurationNode node2, ConfigurationNode child, List<ConfigurationNode> children2)
122    {
123        List<ConfigurationNode> attrs1 = child.getAttributes();
124        List<ConfigurationNode> nodes = new ArrayList<ConfigurationNode>();
125
126        List<ConfigurationNode> children = node2.getChildren(child.getName());
127        Iterator<ConfigurationNode> it = children.iterator();
128        while (it.hasNext())
129        {
130            ConfigurationNode node = it.next();
131            Iterator<ConfigurationNode> iter = attrs1.iterator();
132            while (iter.hasNext())
133            {
134                ConfigurationNode attr1 = iter.next();
135                List<ConfigurationNode> list2 = node.getAttributes(attr1.getName());
136                if (list2.size() == 1
137                    && !attr1.getValue().equals(list2.get(0).getValue()))
138                {
139                    node = null;
140                    break;
141                }
142            }
143            if (node != null)
144            {
145                nodes.add(node);
146            }
147        }
148
149        if (nodes.size() == 1)
150        {
151            return nodes.get(0);
152        }
153        if (nodes.size() > 1 && !isListNode(child))
154        {
155            Iterator<ConfigurationNode> iter = nodes.iterator();
156            while (iter.hasNext())
157            {
158                children2.remove(iter.next());
159            }
160        }
161
162        return null;
163    }
164}