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 that performs a merge from two passed in node 029 * 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 * Combines the given nodes to a new union node. 046 * 047 * @param node1 the first source node 048 * @param node2 the second source node 049 * @return the union node 050 */ 051 052 @Override 053 public ImmutableNode combine(final ImmutableNode node1, final ImmutableNode node2) { 054 final ImmutableNode.Builder result = new ImmutableNode.Builder(); 055 result.name(node1.getNodeName()); 056 result.value(node1.getValue()); 057 addAttributes(result, node1, node2); 058 059 // Check if nodes can be combined 060 final List<ImmutableNode> children2 = new LinkedList<>(node2.getChildren()); 061 node1.forEach(child1 -> { 062 final ImmutableNode child2 = canCombine(node2, child1, children2); 063 if (child2 != null) { 064 result.addChild(combine(child1, child2)); 065 children2.remove(child2); 066 } else { 067 result.addChild(child1); 068 } 069 }); 070 071 // Add remaining children of node 2 072 children2.forEach(result::addChild); 073 return result.create(); 074 } 075 076 /** 077 * Handles the attributes during a combination process. First all attributes of the first node will be added to the 078 * result. Then all attributes of the second node, which are not contained in the first node, will also be added. 079 * 080 * @param result the builder for the resulting node 081 * @param node1 the first node 082 * @param node2 the second node 083 */ 084 protected void addAttributes(final ImmutableNode.Builder result, final ImmutableNode node1, final ImmutableNode node2) { 085 final Map<String, Object> attributes = new HashMap<>(node1.getAttributes()); 086 node2.getAttributes().forEach(attributes::putIfAbsent); 087 result.addAttributes(attributes); 088 } 089 090 /** 091 * Tests if the first node can be combined with the second node. A node can only be combined if its attributes are all 092 * present in the second node and they all have the same value. 093 * 094 * @param node2 the second node 095 * @param child the child node (of the first node) 096 * @param children2 the children of the 2nd node 097 * @return a child of the second node, with which a combination is possible 098 */ 099 protected ImmutableNode canCombine(final ImmutableNode node2, final ImmutableNode child, final List<ImmutableNode> children2) { 100 final Map<String, Object> attrs1 = child.getAttributes(); 101 final List<ImmutableNode> nodes = new ArrayList<>(); 102 103 final List<ImmutableNode> children = HANDLER.getChildren(node2, child.getNodeName()); 104 children.forEach(node -> { 105 if (matchAttributes(attrs1, node)) { 106 nodes.add(node); 107 } 108 }); 109 110 if (nodes.size() == 1) { 111 return nodes.get(0); 112 } 113 if (nodes.size() > 1 && !isListNode(child)) { 114 nodes.forEach(children2::remove); 115 } 116 117 return null; 118 } 119 120 /** 121 * Checks whether the attributes of the passed in node are compatible. 122 * 123 * @param attrs1 the attributes of the first node 124 * @param node the 2nd node 125 * @return a flag whether these nodes can be combined regarding their attributes 126 */ 127 private static boolean matchAttributes(final Map<String, Object> attrs1, final ImmutableNode node) { 128 final Map<String, Object> attrs2 = node.getAttributes(); 129 for (final Map.Entry<String, Object> e : attrs1.entrySet()) { 130 if (attrs2.containsKey(e.getKey()) && !Objects.equals(e.getValue(), attrs2.get(e.getKey()))) { 131 return false; 132 } 133 } 134 return true; 135 } 136}