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.Iterator;
020 import java.util.LinkedList;
021 import java.util.List;
022 import java.util.ArrayList;
023
024 /**
025 * <p>
026 * A specialized implementation of the <code>NodeCombiner</code> 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 764168 2009-04-11 06:23:13Z rgoers $
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 public ConfigurationNode combine(ConfigurationNode node1, ConfigurationNode node2)
056 {
057 ViewNode result = createViewNode();
058 result.setName(node1.getName());
059 result.setValue(node1.getValue());
060 addAttributes(result, node1, node2);
061
062 // Check if nodes can be combined
063 List children2 = new LinkedList(node2.getChildren());
064 for (Iterator it = node1.getChildren().iterator(); it.hasNext();)
065 {
066 ConfigurationNode child1 = (ConfigurationNode) it.next();
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 (Iterator it = children2.iterator(); it.hasNext();)
081 {
082 result.addChild((ConfigurationNode) it.next());
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 (Iterator it = node2.getAttributes().iterator(); it.hasNext();)
102 {
103 ConfigurationNode attr = (ConfigurationNode) it.next();
104 if (node1.getAttributeCount(attr.getName()) == 0)
105 {
106 result.addAttribute(attr);
107 }
108 }
109 }
110
111 /**
112 * Tests if the first node can be combined with the second node. A node can
113 * only be combined if its attributes are all present in the second node and
114 * they all have the same value.
115 *
116 * @param node1 the first node
117 * @param node2 the second node
118 * @param child the child node (of the first node)
119 * @return a child of the second node, with which a combination is possible
120 */
121 protected ConfigurationNode canCombine(ConfigurationNode node1,
122 ConfigurationNode node2, ConfigurationNode child, List children2)
123 {
124 List attrs1 = child.getAttributes();
125 List nodes = new ArrayList();
126
127 List children = node2.getChildren(child.getName());
128 Iterator it = children.iterator();
129 while (it.hasNext())
130 {
131 ConfigurationNode node = (ConfigurationNode) it.next();
132 Iterator iter = attrs1.iterator();
133 while (iter.hasNext())
134 {
135 ConfigurationNode attr1 = (ConfigurationNode) iter.next();
136 List list2 = node.getAttributes(attr1.getName());
137 if (list2.size() == 1
138 && !attr1.getValue().equals(((ConfigurationNode) list2.get(0)).getValue()))
139 {
140 node = null;
141 break;
142 }
143 }
144 if (node != null)
145 {
146 nodes.add(node);
147 }
148 }
149
150 if (nodes.size() == 1)
151 {
152 return (ConfigurationNode) nodes.get(0);
153 }
154 if (nodes.size() > 1 && !isListNode(child))
155 {
156 Iterator iter = nodes.iterator();
157 while (iter.hasNext())
158 {
159 children2.remove(iter.next());
160 }
161 }
162
163 return null;
164 }
165 }