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; 020 021 /** 022 * <p> 023 * A concrete combiner implementation that is able to construct an override 024 * combination. 025 * </p> 026 * <p> 027 * An <em>override combination</em> means that nodes in the first node 028 * structure take precedence over nodes in the second, or - in other words - 029 * nodes of the second structure are only added to the resulting structure if 030 * they do not occure in the first one. This is especially suitable for dealing 031 * with the properties of configurations that are defined in an 032 * <code>override</code> section of a configuration definition file (hence the 033 * name). 034 * </p> 035 * <p> 036 * This combiner will iterate over the second node hierarchy and find all nodes 037 * that are not contained in the first hierarchy; these are added to the result. 038 * If a node can be found in both structures, it is checked whether a 039 * combination (in a recursive way) can be constructed for the two, which will 040 * then be added. Per default, nodes are combined, which occur only once in both 041 * structures. This test is implemented in the <code>canCombine()</code> 042 * method. 043 * </p> 044 * <p> 045 * As is true for the <code>{@link UnionCombiner}</code>, for this combiner 046 * list nodes are important. The <code>addListNode()</code> can be called to 047 * declare certain nodes as list nodes. This has the effect that these nodes 048 * will never be combined. 049 * </p> 050 * 051 * @author <a 052 * href="http://commons.apache.org/configuration/team-list.html">Commons 053 * Configuration team</a> 054 * @version $Id: OverrideCombiner.java 561230 2007-07-31 04:17:09Z rahul $ 055 * @since 1.3 056 */ 057 public class OverrideCombiner extends NodeCombiner 058 { 059 /** 060 * Constructs an override combination for the passed in node structures. 061 * 062 * @param node1 the first node 063 * @param node2 the second node 064 * @return the resulting combined node structure 065 */ 066 public ConfigurationNode combine(ConfigurationNode node1, 067 ConfigurationNode node2) 068 { 069 ViewNode result = createViewNode(); 070 result.setName(node1.getName()); 071 072 // Process nodes from the first structure, which override the second 073 for (Iterator it = node1.getChildren().iterator(); it.hasNext();) 074 { 075 ConfigurationNode child = (ConfigurationNode) it.next(); 076 ConfigurationNode child2 = canCombine(node1, node2, child); 077 if (child2 != null) 078 { 079 result.addChild(combine(child, child2)); 080 } 081 else 082 { 083 result.addChild(child); 084 } 085 } 086 087 // Process nodes from the second structure, which are not contained 088 // in the first structure 089 for (Iterator it = node2.getChildren().iterator(); it.hasNext();) 090 { 091 ConfigurationNode child = (ConfigurationNode) it.next(); 092 if (node1.getChildrenCount(child.getName()) < 1) 093 { 094 result.addChild(child); 095 } 096 } 097 098 // Handle attributes and value 099 addAttributes(result, node1, node2); 100 result.setValue((node1.getValue() != null) ? node1.getValue() : node2 101 .getValue()); 102 103 return result; 104 } 105 106 /** 107 * Handles the attributes during a combination process. First all attributes 108 * of the first node will be added to the result. Then all attributes of the 109 * second node, which are not contained in the first node, will also be 110 * added. 111 * 112 * @param result the resulting node 113 * @param node1 the first node 114 * @param node2 the second node 115 */ 116 protected void addAttributes(ViewNode result, ConfigurationNode node1, 117 ConfigurationNode node2) 118 { 119 result.appendAttributes(node1); 120 for (Iterator it = node2.getAttributes().iterator(); it.hasNext();) 121 { 122 ConfigurationNode attr = (ConfigurationNode) it.next(); 123 if (node1.getAttributeCount(attr.getName()) == 0) 124 { 125 result.addAttribute(attr); 126 } 127 } 128 } 129 130 /** 131 * Tests if a child node of the second node can be combined with the given 132 * child node of the first node. If this is the case, the corresponding node 133 * will be returned, otherwise <b>null</b>. This implementation checks 134 * whether the child node occurs only once in both hierarchies and is no 135 * known list node. 136 * 137 * @param node1 the first node 138 * @param node2 the second node 139 * @param child the child node (of the first node) 140 * @return a child of the second node, with which a combination is possible 141 */ 142 protected ConfigurationNode canCombine(ConfigurationNode node1, 143 ConfigurationNode node2, ConfigurationNode child) 144 { 145 if (node2.getChildrenCount(child.getName()) == 1 146 && node1.getChildrenCount(child.getName()) == 1 147 && !isListNode(child)) 148 { 149 return (ConfigurationNode) node2.getChildren(child.getName()) 150 .get(0); 151 } 152 else 153 { 154 return null; 155 } 156 } 157 }