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; 018 019 020/** 021 * <p> 022 * A concrete combiner implementation that is able to construct an override 023 * combination. 024 * </p> 025 * <p> 026 * An <em>override combination</em> means that nodes in the first node 027 * structure take precedence over nodes in the second, or - in other words - 028 * nodes of the second structure are only added to the resulting structure if 029 * they do not occur in the first one. This is especially suitable for dealing 030 * with the properties of configurations that are defined in an 031 * {@code override} section of a configuration definition file (hence the 032 * name). 033 * </p> 034 * <p> 035 * This combiner will iterate over the second node hierarchy and find all nodes 036 * that are not contained in the first hierarchy; these are added to the result. 037 * If a node can be found in both structures, it is checked whether a 038 * combination (in a recursive way) can be constructed for the two, which will 039 * then be added. Per default, nodes are combined, which occur only once in both 040 * structures. This test is implemented in the {@code canCombine()} 041 * method. 042 * </p> 043 * <p> 044 * As is true for the {@link UnionCombiner}, for this combiner 045 * list nodes are important. The {@code addListNode()} can be called to 046 * declare certain nodes as list nodes. This has the effect that these nodes 047 * will never be combined. 048 * </p> 049 * 050 * @author <a 051 * href="http://commons.apache.org/configuration/team-list.html">Commons 052 * Configuration team</a> 053 * @version $Id: OverrideCombiner.java 1301991 2012-03-17 20:18:02Z sebb $ 054 * @since 1.3 055 */ 056public class OverrideCombiner extends NodeCombiner 057{ 058 /** 059 * Constructs an override combination for the passed in node structures. 060 * 061 * @param node1 the first node 062 * @param node2 the second node 063 * @return the resulting combined node structure 064 */ 065 @Override 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 (ConfigurationNode child : node1.getChildren()) 074 { 075 ConfigurationNode child2 = canCombine(node1, node2, child); 076 if (child2 != null) 077 { 078 result.addChild(combine(child, child2)); 079 } 080 else 081 { 082 result.addChild(child); 083 } 084 } 085 086 // Process nodes from the second structure, which are not contained 087 // in the first structure 088 for (ConfigurationNode child : node2.getChildren()) 089 { 090 if (node1.getChildrenCount(child.getName()) < 1) 091 { 092 result.addChild(child); 093 } 094 } 095 096 // Handle attributes and value 097 addAttributes(result, node1, node2); 098 result.setValue((node1.getValue() != null) ? node1.getValue() : node2 099 .getValue()); 100 101 return result; 102 } 103 104 /** 105 * Handles the attributes during a combination process. First all attributes 106 * of the first node will be added to the result. Then all attributes of the 107 * second node, which are not contained in the first node, will also be 108 * added. 109 * 110 * @param result the resulting node 111 * @param node1 the first node 112 * @param node2 the second node 113 */ 114 protected void addAttributes(ViewNode result, ConfigurationNode node1, 115 ConfigurationNode node2) 116 { 117 result.appendAttributes(node1); 118 for (ConfigurationNode attr : node2.getAttributes()) 119 { 120 if (node1.getAttributeCount(attr.getName()) == 0) 121 { 122 result.addAttribute(attr); 123 } 124 } 125 } 126 127 /** 128 * Tests if a child node of the second node can be combined with the given 129 * child node of the first node. If this is the case, the corresponding node 130 * will be returned, otherwise <b>null</b>. This implementation checks 131 * whether the child node occurs only once in both hierarchies and is no 132 * known list node. 133 * 134 * @param node1 the first node 135 * @param node2 the second node 136 * @param child the child node (of the first node) 137 * @return a child of the second node, with which a combination is possible 138 */ 139 protected ConfigurationNode canCombine(ConfigurationNode node1, 140 ConfigurationNode node2, ConfigurationNode child) 141 { 142 if (node2.getChildrenCount(child.getName()) == 1 143 && node1.getChildrenCount(child.getName()) == 1 144 && !isListNode(child)) 145 { 146 return node2.getChildren(child.getName()).get(0); 147 } 148 else 149 { 150 return null; 151 } 152 } 153}