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 * @version $Id: MergeCombiner.java 1842194 2018-09-27 22:24:23Z ggregory $ 042 * @since 1.7 043 */ 044public class MergeCombiner extends NodeCombiner 045{ 046 /** 047 * Combines the given nodes to a new union node. 048 * 049 * @param node1 the first source node 050 * @param node2 the second source node 051 * @return the union node 052 */ 053 054 @Override 055 public ImmutableNode combine(final ImmutableNode node1, final ImmutableNode node2) 056 { 057 final ImmutableNode.Builder result = new ImmutableNode.Builder(); 058 result.name(node1.getNodeName()); 059 result.value(node1.getValue()); 060 addAttributes(result, node1, node2); 061 062 // Check if nodes can be combined 063 final List<ImmutableNode> children2 = new LinkedList<>(node2.getChildren()); 064 for (final ImmutableNode child1 : node1.getChildren()) 065 { 066 final ImmutableNode child2 = canCombine(node2, child1, children2); 067 if (child2 != null) 068 { 069 result.addChild(combine(child1, child2)); 070 children2.remove(child2); 071 } 072 else 073 { 074 result.addChild(child1); 075 } 076 } 077 078 // Add remaining children of node 2 079 for (final ImmutableNode c : children2) 080 { 081 result.addChild(c); 082 } 083 return result.create(); 084 } 085 086 /** 087 * Handles the attributes during a combination process. First all attributes 088 * of the first node will be added to the result. Then all attributes of the 089 * second node, which are not contained in the first node, will also be 090 * added. 091 * 092 * @param result the builder for the resulting node 093 * @param node1 the first node 094 * @param node2 the second node 095 */ 096 protected void addAttributes(final ImmutableNode.Builder result, final ImmutableNode node1, 097 final ImmutableNode node2) 098 { 099 final Map<String, Object> attributes = new HashMap<>(); 100 attributes.putAll(node1.getAttributes()); 101 for (final Map.Entry<String, Object> e : node2.getAttributes().entrySet()) 102 { 103 if (!attributes.containsKey(e.getKey())) 104 { 105 attributes.put(e.getKey(), e.getValue()); 106 } 107 } 108 result.addAttributes(attributes); 109 } 110 111 /** 112 * Tests if the first node can be combined with the second node. A node can 113 * only be combined if its attributes are all present in the second node and 114 * they all have the same value. 115 * 116 * @param node2 the second node 117 * @param child the child node (of the first node) 118 * @param children2 the children of the 2nd node 119 * @return a child of the second node, with which a combination is possible 120 */ 121 protected ImmutableNode canCombine(final ImmutableNode node2, 122 final ImmutableNode child, final List<ImmutableNode> children2) 123 { 124 final Map<String, Object> attrs1 = child.getAttributes(); 125 final List<ImmutableNode> nodes = new ArrayList<>(); 126 127 final List<ImmutableNode> children = 128 HANDLER.getChildren(node2, child.getNodeName()); 129 for (final ImmutableNode node : children) 130 { 131 if (matchAttributes(attrs1, node)) 132 { 133 nodes.add(node); 134 } 135 } 136 137 if (nodes.size() == 1) 138 { 139 return nodes.get(0); 140 } 141 if (nodes.size() > 1 && !isListNode(child)) 142 { 143 for (final ImmutableNode node : nodes) 144 { 145 children2.remove(node); 146 } 147 } 148 149 return null; 150 } 151 152 /** 153 * Checks whether the attributes of the passed in node are compatible. 154 * 155 * @param attrs1 the attributes of the first node 156 * @param node the 2nd node 157 * @return a flag whether these nodes can be combined regarding their 158 * attributes 159 */ 160 private static boolean matchAttributes(final Map<String, Object> attrs1, 161 final ImmutableNode node) 162 { 163 final Map<String, Object> attrs2 = node.getAttributes(); 164 for (final Map.Entry<String, Object> e : attrs1.entrySet()) 165 { 166 if (attrs2.containsKey(e.getKey()) 167 && !Objects 168 .equals(e.getValue(), attrs2.get(e.getKey()))) 169 { 170 return false; 171 } 172 } 173 return true; 174 } 175}