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 }