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 019import java.util.ArrayList; 020import java.util.HashMap; 021import java.util.LinkedList; 022import java.util.List; 023import java.util.Map; 024import java.util.Objects; 025 026/** 027 * <p> 028 * A specialized implementation of the {@code NodeCombiner} interface 029 * that performs a merge from two passed in node hierarchies. 030 * </p> 031 * <p> 032 * This combiner performs the merge using a few rules: 033 * </p> 034 * <ol> 035 * <li>Nodes can be merged when attributes that appear in both have the same value.</li> 036 * <li>Only a single node in the second file is considered a match to the node in the first file.</li> 037 * <li>Attributes in nodes that match are merged. 038 * <li>Nodes in both files that do not match are added to the result.</li> 039 * </ol> 040 * 041 * @since 1.7 042 */ 043public class MergeCombiner extends NodeCombiner 044{ 045 /** 046 * Combines the given nodes to a new union node. 047 * 048 * @param node1 the first source node 049 * @param node2 the second source node 050 * @return the union node 051 */ 052 053 @Override 054 public ImmutableNode combine(final ImmutableNode node1, final ImmutableNode node2) 055 { 056 final ImmutableNode.Builder result = new ImmutableNode.Builder(); 057 result.name(node1.getNodeName()); 058 result.value(node1.getValue()); 059 addAttributes(result, node1, node2); 060 061 // Check if nodes can be combined 062 final List<ImmutableNode> children2 = new LinkedList<>(node2.getChildren()); 063 for (final ImmutableNode child1 : node1.getChildren()) 064 { 065 final ImmutableNode child2 = canCombine(node2, child1, children2); 066 if (child2 != null) 067 { 068 result.addChild(combine(child1, child2)); 069 children2.remove(child2); 070 } 071 else 072 { 073 result.addChild(child1); 074 } 075 } 076 077 // Add remaining children of node 2 078 for (final ImmutableNode c : children2) 079 { 080 result.addChild(c); 081 } 082 return result.create(); 083 } 084 085 /** 086 * Handles the attributes during a combination process. First all attributes 087 * of the first node will be added to the result. Then all attributes of the 088 * second node, which are not contained in the first node, will also be 089 * added. 090 * 091 * @param result the builder for the resulting node 092 * @param node1 the first node 093 * @param node2 the second node 094 */ 095 protected void addAttributes(final ImmutableNode.Builder result, final ImmutableNode node1, 096 final ImmutableNode node2) 097 { 098 final Map<String, Object> attributes = new HashMap<>(); 099 attributes.putAll(node1.getAttributes()); 100 for (final Map.Entry<String, Object> e : node2.getAttributes().entrySet()) 101 { 102 if (!attributes.containsKey(e.getKey())) 103 { 104 attributes.put(e.getKey(), e.getValue()); 105 } 106 } 107 result.addAttributes(attributes); 108 } 109 110 /** 111 * Tests if the first node can be combined with the second node. A node can 112 * only be combined if its attributes are all present in the second node and 113 * they all have the same value. 114 * 115 * @param node2 the second node 116 * @param child the child node (of the first node) 117 * @param children2 the children of the 2nd node 118 * @return a child of the second node, with which a combination is possible 119 */ 120 protected ImmutableNode canCombine(final ImmutableNode node2, 121 final ImmutableNode child, final List<ImmutableNode> children2) 122 { 123 final Map<String, Object> attrs1 = child.getAttributes(); 124 final List<ImmutableNode> nodes = new ArrayList<>(); 125 126 final List<ImmutableNode> children = 127 HANDLER.getChildren(node2, child.getNodeName()); 128 for (final ImmutableNode node : children) 129 { 130 if (matchAttributes(attrs1, node)) 131 { 132 nodes.add(node); 133 } 134 } 135 136 if (nodes.size() == 1) 137 { 138 return nodes.get(0); 139 } 140 if (nodes.size() > 1 && !isListNode(child)) 141 { 142 for (final ImmutableNode node : nodes) 143 { 144 children2.remove(node); 145 } 146 } 147 148 return null; 149 } 150 151 /** 152 * Checks whether the attributes of the passed in node are compatible. 153 * 154 * @param attrs1 the attributes of the first node 155 * @param node the 2nd node 156 * @return a flag whether these nodes can be combined regarding their 157 * attributes 158 */ 159 private static boolean matchAttributes(final Map<String, Object> attrs1, 160 final ImmutableNode node) 161 { 162 final Map<String, Object> attrs2 = node.getAttributes(); 163 for (final Map.Entry<String, Object> e : attrs1.entrySet()) 164 { 165 if (attrs2.containsKey(e.getKey()) 166 && !Objects 167 .equals(e.getValue(), attrs2.get(e.getKey()))) 168 { 169 return false; 170 } 171 } 172 return true; 173 } 174}