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.configuration2.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 * @since 1.3 051 */ 052public class OverrideCombiner extends NodeCombiner 053{ 054 /** 055 * Constructs an override combination for the passed in node structures. 056 * 057 * @param node1 the first node 058 * @param node2 the second node 059 * @return the resulting combined node structure 060 */ 061 @Override 062 public ImmutableNode combine(final ImmutableNode node1, 063 final ImmutableNode node2) 064 { 065 final ImmutableNode.Builder result = new ImmutableNode.Builder(); 066 result.name(node1.getNodeName()); 067 068 // Process nodes from the first structure, which override the second 069 for (final ImmutableNode child : node1.getChildren()) 070 { 071 final ImmutableNode child2 = canCombine(node1, node2, child); 072 if (child2 != null) 073 { 074 result.addChild(combine(child, child2)); 075 } 076 else 077 { 078 result.addChild(child); 079 } 080 } 081 082 // Process nodes from the second structure, which are not contained 083 // in the first structure 084 for (final ImmutableNode child : node2.getChildren()) 085 { 086 if (HANDLER.getChildrenCount(node1, child.getNodeName()) < 1) 087 { 088 result.addChild(child); 089 } 090 } 091 092 // Handle attributes and value 093 addAttributes(result, node1, node2); 094 result.value(node1.getValue() != null ? node1.getValue() : node2 095 .getValue()); 096 097 return result.create(); 098 } 099 100 /** 101 * Handles the attributes during a combination process. First all attributes 102 * of the first node are added to the result. Then all attributes of the 103 * second node, which are not contained in the first node, are also added. 104 * 105 * @param result the resulting node 106 * @param node1 the first node 107 * @param node2 the second node 108 */ 109 protected void addAttributes(final ImmutableNode.Builder result, 110 final ImmutableNode node1, final ImmutableNode node2) 111 { 112 result.addAttributes(node1.getAttributes()); 113 for (final String attr : node2.getAttributes().keySet()) 114 { 115 if (!node1.getAttributes().containsKey(attr)) 116 { 117 result.addAttribute(attr, 118 HANDLER.getAttributeValue(node2, attr)); 119 } 120 } 121 } 122 123 /** 124 * Tests if a child node of the second node can be combined with the given 125 * child node of the first node. If this is the case, the corresponding node 126 * will be returned, otherwise <b>null</b>. This implementation checks 127 * whether the child node occurs only once in both hierarchies and is no 128 * known list node. 129 * 130 * @param node1 the first node 131 * @param node2 the second node 132 * @param child the child node (of the first node) 133 * @return a child of the second node, with which a combination is possible 134 */ 135 protected ImmutableNode canCombine(final ImmutableNode node1, 136 final ImmutableNode node2, final ImmutableNode child) 137 { 138 if (HANDLER.getChildrenCount(node2, child.getNodeName()) == 1 139 && HANDLER.getChildrenCount(node1, child.getNodeName()) == 1 140 && !isListNode(child)) 141 { 142 return HANDLER.getChildren(node2, child.getNodeName()).get(0); 143 } 144 return null; 145 } 146}