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.configuration2.tree;
18
19 import java.util.ArrayList;
20 import java.util.HashMap;
21 import java.util.LinkedList;
22 import java.util.List;
23 import java.util.Map;
24 import java.util.Objects;
25
26 /**
27 * <p>
28 * A specialized implementation of the {@code NodeCombiner} interface that performs a merge from two passed in node
29 * hierarchies.
30 * </p>
31 * <p>
32 * This combiner performs the merge using a few rules:
33 * </p>
34 * <ol>
35 * <li>Nodes can be merged when attributes that appear in both have the same value.</li>
36 * <li>Only a single node in the second file is considered a match to the node in the first file.</li>
37 * <li>Attributes in nodes that match are merged.
38 * <li>Nodes in both files that do not match are added to the result.</li>
39 * </ol>
40 *
41 * @since 1.7
42 */
43 public class MergeCombiner extends NodeCombiner {
44 /**
45 * Combines the given nodes to a new union node.
46 *
47 * @param node1 the first source node
48 * @param node2 the second source node
49 * @return the union node
50 */
51
52 @Override
53 public ImmutableNode combine(final ImmutableNode node1, final ImmutableNode node2) {
54 final ImmutableNode.Builder result = new ImmutableNode.Builder();
55 result.name(node1.getNodeName());
56 result.value(node1.getValue());
57 addAttributes(result, node1, node2);
58
59 // Check if nodes can be combined
60 final List<ImmutableNode> children2 = new LinkedList<>(node2.getChildren());
61 node1.forEach(child1 -> {
62 final ImmutableNode child2 = canCombine(node2, child1, children2);
63 if (child2 != null) {
64 result.addChild(combine(child1, child2));
65 children2.remove(child2);
66 } else {
67 result.addChild(child1);
68 }
69 });
70
71 // Add remaining children of node 2
72 children2.forEach(result::addChild);
73 return result.create();
74 }
75
76 /**
77 * Handles the attributes during a combination process. First all attributes of the first node will be added to the
78 * result. Then all attributes of the second node, which are not contained in the first node, will also be added.
79 *
80 * @param result the builder for the resulting node
81 * @param node1 the first node
82 * @param node2 the second node
83 */
84 protected void addAttributes(final ImmutableNode.Builder result, final ImmutableNode node1, final ImmutableNode node2) {
85 final Map<String, Object> attributes = new HashMap<>(node1.getAttributes());
86 node2.getAttributes().forEach(attributes::putIfAbsent);
87 result.addAttributes(attributes);
88 }
89
90 /**
91 * Tests if the first node can be combined with the second node. A node can only be combined if its attributes are all
92 * present in the second node and they all have the same value.
93 *
94 * @param node2 the second node
95 * @param child the child node (of the first node)
96 * @param children2 the children of the 2nd node
97 * @return a child of the second node, with which a combination is possible
98 */
99 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 }