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.IdentityHashMap;
22 import java.util.Map;
23
24 import org.eclipse.aether.graph.DependencyNode;
25 import org.eclipse.aether.graph.DependencyVisitor;
26
27 import static java.util.Objects.requireNonNull;
28
29 /**
30 * A dependency visitor that delegates to another visitor if a node hasn't been visited before. In other words, this
31 * visitor provides a tree-view of a dependency graph which generally can have multiple paths to the same node or even
32 * cycles.
33 */
34 public final class TreeDependencyVisitor implements DependencyVisitor {
35
36 private final Map<DependencyNode, Object> visitedNodes;
37
38 private final DependencyVisitor visitor;
39
40 private final Stack<Boolean> visits;
41
42 /**
43 * Creates a new visitor that delegates to the specified visitor.
44 *
45 * @param visitor The visitor to delegate to, must not be {@code null}.
46 */
47 public TreeDependencyVisitor(DependencyVisitor visitor) {
48 this.visitor = requireNonNull(visitor, "dependency visitor delegate cannot be null");
49 visitedNodes = new IdentityHashMap<>(512);
50 visits = new Stack<>();
51 }
52
53 @Override
54 public boolean visitEnter(DependencyNode node) {
55 boolean visited = visitedNodes.put(node, Boolean.TRUE) != null;
56
57 visits.push(visited);
58
59 if (visited) {
60 return false;
61 }
62
63 return visitor.visitEnter(node);
64 }
65
66 @Override
67 public boolean visitLeave(DependencyNode node) {
68 Boolean visited = visits.pop();
69
70 if (visited) {
71 return true;
72 }
73
74 return visitor.visitLeave(node);
75 }
76 }