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 package org.apache.commons.configuration.tree;
018
019 import java.util.ArrayList;
020 import java.util.Iterator;
021 import java.util.LinkedList;
022 import 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 1206480 2011-11-26 16:28:58Z oheger $
043 * @since 1.7
044 */
045 public 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 (ConfigurationNode) 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 }