1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 package org.apache.commons.configuration.tree; 18 19 20 /** 21 * <p> 22 * A concrete combiner implementation that is able to construct an override 23 * combination. 24 * </p> 25 * <p> 26 * An <em>override combination</em> means that nodes in the first node 27 * structure take precedence over nodes in the second, or - in other words - 28 * nodes of the second structure are only added to the resulting structure if 29 * they do not occur in the first one. This is especially suitable for dealing 30 * with the properties of configurations that are defined in an 31 * {@code override} section of a configuration definition file (hence the 32 * name). 33 * </p> 34 * <p> 35 * This combiner will iterate over the second node hierarchy and find all nodes 36 * that are not contained in the first hierarchy; these are added to the result. 37 * If a node can be found in both structures, it is checked whether a 38 * combination (in a recursive way) can be constructed for the two, which will 39 * then be added. Per default, nodes are combined, which occur only once in both 40 * structures. This test is implemented in the {@code canCombine()} 41 * method. 42 * </p> 43 * <p> 44 * As is true for the {@link UnionCombiner}, for this combiner 45 * list nodes are important. The {@code addListNode()} can be called to 46 * declare certain nodes as list nodes. This has the effect that these nodes 47 * will never be combined. 48 * </p> 49 * 50 * @author <a 51 * href="http://commons.apache.org/configuration/team-list.html">Commons 52 * Configuration team</a> 53 * @version $Id: OverrideCombiner.java 1301991 2012-03-17 20:18:02Z sebb $ 54 * @since 1.3 55 */ 56 public class OverrideCombiner extends NodeCombiner 57 { 58 /** 59 * Constructs an override combination for the passed in node structures. 60 * 61 * @param node1 the first node 62 * @param node2 the second node 63 * @return the resulting combined node structure 64 */ 65 @Override 66 public ConfigurationNode combine(ConfigurationNode node1, 67 ConfigurationNode node2) 68 { 69 ViewNode result = createViewNode(); 70 result.setName(node1.getName()); 71 72 // Process nodes from the first structure, which override the second 73 for (ConfigurationNode child : node1.getChildren()) 74 { 75 ConfigurationNode child2 = canCombine(node1, node2, child); 76 if (child2 != null) 77 { 78 result.addChild(combine(child, child2)); 79 } 80 else 81 { 82 result.addChild(child); 83 } 84 } 85 86 // Process nodes from the second structure, which are not contained 87 // in the first structure 88 for (ConfigurationNode child : node2.getChildren()) 89 { 90 if (node1.getChildrenCount(child.getName()) < 1) 91 { 92 result.addChild(child); 93 } 94 } 95 96 // Handle attributes and value 97 addAttributes(result, node1, node2); 98 result.setValue((node1.getValue() != null) ? node1.getValue() : node2 99 .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 }