1 package org.eclipse.aether.util.graph.visitor;
2
3 /*
4 * Licensed to the Apache Software Foundation (ASF) under one
5 * or more contributor license agreements. See the NOTICE file
6 * distributed with this work for additional information
7 * regarding copyright ownership. The ASF licenses this file
8 * to you under the Apache License, Version 2.0 (the
9 * "License"); you may not use this file except in compliance
10 * with the License. You may obtain a copy of the License at
11 *
12 * http://www.apache.org/licenses/LICENSE-2.0
13 *
14 * Unless required by applicable law or agreed to in writing,
15 * software distributed under the License is distributed on an
16 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17 * KIND, either express or implied. See the License for the
18 * specific language governing permissions and limitations
19 * under the License.
20 */
21
22 import java.util.IdentityHashMap;
23 import java.util.Map;
24
25 import org.eclipse.aether.graph.DependencyNode;
26 import org.eclipse.aether.graph.DependencyVisitor;
27
28 /**
29 * A dependency visitor that delegates to another visitor if a node hasn't been visited before. In other words, this
30 * visitor provides a tree-view of a dependency graph which generally can have multiple paths to the same node or even
31 * cycles.
32 */
33 public final class TreeDependencyVisitor
34 implements DependencyVisitor
35 {
36
37 private final Map<DependencyNode, Object> visitedNodes;
38
39 private final DependencyVisitor visitor;
40
41 private final Stack<Boolean> visits;
42
43 /**
44 * Creates a new visitor that delegates to the specified visitor.
45 *
46 * @param visitor The visitor to delegate to, must not be {@code null}.
47 */
48 public TreeDependencyVisitor( DependencyVisitor visitor )
49 {
50 if ( visitor == null )
51 {
52 throw new IllegalArgumentException( "no visitor delegate specified" );
53 }
54 this.visitor = visitor;
55 visitedNodes = new IdentityHashMap<DependencyNode, Object>( 512 );
56 visits = new Stack<Boolean>();
57 }
58
59 public boolean visitEnter( DependencyNode node )
60 {
61 boolean visited = visitedNodes.put( node, Boolean.TRUE ) != null;
62
63 visits.push( visited );
64
65 if ( visited )
66 {
67 return false;
68 }
69
70 return visitor.visitEnter( node );
71 }
72
73 public boolean visitLeave( DependencyNode node )
74 {
75 Boolean visited = visits.pop();
76
77 if ( visited )
78 {
79 return true;
80 }
81
82 return visitor.visitLeave( node );
83 }
84
85 }