1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 */
19 package org.eclipse.aether.util.graph.visitor;
20
21 import java.util.function.Consumer;
22
23 import org.eclipse.aether.ConfigurationProperties;
24 import org.eclipse.aether.graph.DependencyNode;
25
26 /**
27 * Processes dependency graph by traversing the graph in postorder. This visitor visits each node exactly once
28 * regardless how many paths within the dependency graph lead to the node such that the resulting node sequence is
29 * free of duplicates.
30 *
31 * @since 2.0.0
32 *
33 * @see NodeListGenerator
34 */
35 public final class PostorderDependencyNodeConsumerVisitor extends AbstractDependencyNodeConsumerVisitor {
36
37 public static final String NAME = ConfigurationProperties.REPOSITORY_SYSTEM_DEPENDENCY_VISITOR_POSTORDER;
38
39 private final Stack<Boolean> visits;
40
41 /**
42 * Creates a new postorder list generator.
43 */
44 public PostorderDependencyNodeConsumerVisitor(Consumer<DependencyNode> nodeConsumer) {
45 super(nodeConsumer);
46 visits = new Stack<>();
47 }
48
49 @Override
50 public boolean visitEnter(DependencyNode node) {
51 boolean visited = !setVisited(node);
52 visits.push(visited);
53 return !visited;
54 }
55
56 @Override
57 public boolean visitLeave(DependencyNode node) {
58 Boolean visited = visits.pop();
59 if (visited) {
60 return true;
61 }
62 nodeConsumer.accept(node);
63 return true;
64 }
65 }