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 * https://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.io;
18
19 import java.io.IOException;
20 import java.net.URL;
21 import java.util.ArrayList;
22 import java.util.Collection;
23 import java.util.Collections;
24 import java.util.List;
25 import java.util.Set;
26 import java.util.regex.Pattern;
27
28 /**
29 * A specialized implementation of a {@code FileLocationStrategy} which encapsulates an arbitrary number of
30 * {@code FileLocationStrategy} objects.
31 * <p>
32 * A collection with the wrapped {@code FileLocationStrategy} objects is passed at construction time. During a
33 * [{@code locate()} operation the wrapped strategies are called one after the other until one returns a non <strong>null</strong>
34 * URL. This URL is returned. If none of the wrapped strategies is able to resolve the passed in {@link FileLocator},
35 * result is <strong>null</strong>. This is similar to the <em>chain of responsibility</em> design pattern.
36 * </p>
37 * <p>
38 * This class, together with the provided concrete {@code FileLocationStrategy} implementations, offers a convenient way
39 * to customize the lookup for configuration files: Just add the desired concrete strategies to a
40 * {@code CombinedLocationStrategy} object. If necessary, custom strategies can be implemented if there are specific
41 * requirements. Note that the order in which strategies are added to a {@code CombinedLocationStrategy} matters: sub
42 * strategies are queried in the same order as they appear in the collection passed to the constructor.
43 * </p>
44 * <p>
45 * See {@link AbstractFileLocationStrategy} learn how to grant an deny URL schemes and hosts.
46 * </p>
47 *
48 * @see AbstractFileLocationStrategy
49 * @since 2.0
50 */
51 public class CombinedLocationStrategy extends AbstractFileLocationStrategy {
52
53 /**
54 * Builds new instances of {@link CombinedLocationStrategy}.
55 *
56 * @since 2.15.0
57 */
58 public static class Builder extends AbstractBuilder<CombinedLocationStrategy, Builder> {
59
60 /** A collection with all sub strategies managed by this object. */
61 private Collection<? extends FileLocationStrategy> subStrategies;
62
63 /**
64 * Constructs a new instance.
65 */
66 public Builder() {
67 // empty
68 }
69
70 @Override
71 public CombinedLocationStrategy get() throws IOException {
72 return new CombinedLocationStrategy(this);
73 }
74
75 /**
76 * Propagates properties of the parent builder scheme and host to subStrategies.
77 *
78 * @return {@code this} instance.
79 */
80 public Builder propagate() {
81 if (subStrategies != null) {
82 subStrategies.forEach(e -> {
83 if (e instanceof AbstractFileLocationStrategy) {
84 final AbstractFileLocationStrategy afls = (AbstractFileLocationStrategy) e;
85 final Set<String> schemes = afls.getSchemes();
86 schemes.clear();
87 schemes.addAll(getSchemes());
88 final Set<Pattern> hosts = afls.getHosts();
89 hosts.clear();
90 hosts.addAll(getHosts());
91 }
92 });
93 }
94 return asThis();
95 }
96
97 /**
98 * Sets the collection with sub strategies.
99 *
100 * @param subStrategies the collection with sub strategies.
101 * @return {@code this} instance.
102 */
103 public Builder setSubStrategies(final Collection<FileLocationStrategy> subStrategies) {
104 this.subStrategies = subStrategies;
105 return asThis();
106 }
107
108 }
109
110 /** A collection with all sub strategies managed by this object. */
111 private final Collection<FileLocationStrategy> subStrategies;
112
113 /**
114 * Constructs a new instance.
115 *
116 * @param builder How to build the instance.
117 */
118 private CombinedLocationStrategy(final Builder builder) {
119 super(builder);
120 if (builder.subStrategies == null) {
121 throw new IllegalArgumentException("Collection with sub strategies must not be null.");
122 }
123 List<FileLocationStrategy> subStrategiesCopy = new ArrayList<>(builder.subStrategies);
124 if (subStrategiesCopy.contains(null)) {
125 throw new IllegalArgumentException("Collection with sub strategies contains null entry.");
126 }
127 subStrategies = Collections.unmodifiableCollection(subStrategiesCopy);
128 }
129
130 /**
131 * Creates a new instance of {@code CombinedLocationStrategy} and initializes it with the provided sub strategies. The
132 * passed in collection must not be <strong>null</strong> or contain <strong>null</strong> elements.
133 *
134 * @param subs the collection with sub strategies.
135 * @throws IllegalArgumentException if the collection is <strong>null</strong> or has <strong>null</strong> elements.
136 */
137 public CombinedLocationStrategy(final Collection<FileLocationStrategy> subs) {
138 this(new Builder().setSubStrategies(subs));
139 }
140
141 /**
142 * Gets a (unmodifiable) collection with the sub strategies managed by this object.
143 *
144 * @return the sub {@code FileLocationStrategy} objects
145 */
146 public Collection<FileLocationStrategy> getSubStrategies() {
147 return subStrategies;
148 }
149
150 /**
151 * {@inheritDoc} This implementation tries to locate the file by delegating to the managed sub strategies.
152 */
153 @Override
154 public URL locate(final FileSystem fileSystem, final FileLocator locator) {
155 for (final FileLocationStrategy sub : getSubStrategies()) {
156 final URL url = sub.locate(fileSystem, locator);
157 if (url != null) {
158 return check(url);
159 }
160 }
161 return null;
162 }
163 }