001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *     https://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.configuration2.io;
018
019import java.io.IOException;
020import java.net.URL;
021import java.util.ArrayList;
022import java.util.Collection;
023import java.util.Collections;
024import java.util.Set;
025import java.util.regex.Pattern;
026
027/**
028 * A specialized implementation of a {@code FileLocationStrategy} which encapsulates an arbitrary number of
029 * {@code FileLocationStrategy} objects.
030 * <p>
031 * A collection with the wrapped {@code FileLocationStrategy} objects is passed at construction time. During a
032 * [{@code locate()} operation the wrapped strategies are called one after the other until one returns a non <strong>null</strong>
033 * URL. This URL is returned. If none of the wrapped strategies is able to resolve the passed in {@link FileLocator},
034 * result is <strong>null</strong>. This is similar to the <em>chain of responsibility</em> design pattern.
035 * </p>
036 * <p>
037 * This class, together with the provided concrete {@code FileLocationStrategy} implementations, offers a convenient way
038 * to customize the lookup for configuration files: Just add the desired concrete strategies to a
039 * {@code CombinedLocationStrategy} object. If necessary, custom strategies can be implemented if there are specific
040 * requirements. Note that the order in which strategies are added to a {@code CombinedLocationStrategy} matters: sub
041 * strategies are queried in the same order as they appear in the collection passed to the constructor.
042 * </p>
043 * <p>
044 * See {@link AbstractFileLocationStrategy} learn how to grant an deny URL schemes and hosts.
045 * </p>
046 *
047 * @see AbstractFileLocationStrategy
048 * @since 2.0
049 */
050public class CombinedLocationStrategy extends AbstractFileLocationStrategy {
051
052    /**
053     * Builds new instances of {@link CombinedLocationStrategy}.
054     *
055     * @since 2.15.0
056     */
057    public static class Builder extends AbstractBuilder<CombinedLocationStrategy, Builder> {
058
059        /** A collection with all sub strategies managed by this object. */
060        private Collection<? extends FileLocationStrategy> subStrategies;
061
062        /**
063         * Constructs a new instance.
064         */
065        public Builder() {
066            // empty
067        }
068
069        @Override
070        public CombinedLocationStrategy get() throws IOException {
071            return new CombinedLocationStrategy(this);
072        }
073
074        /**
075         * Propagates properties of the parent builder scheme and host to subStrategies.
076         *
077         * @return {@code this} instance.
078         */
079        public Builder propagate() {
080            if (subStrategies != null) {
081                subStrategies.forEach(e -> {
082                    if (e instanceof AbstractFileLocationStrategy) {
083                        final AbstractFileLocationStrategy afls = (AbstractFileLocationStrategy) e;
084                        final Set<String> schemes = afls.getSchemes();
085                        schemes.clear();
086                        schemes.addAll(getSchemes());
087                        final Set<Pattern> hosts = afls.getHosts();
088                        hosts.clear();
089                        hosts.addAll(getHosts());
090                    }
091                });
092            }
093            return asThis();
094        }
095
096        /**
097         * Sets the collection with sub strategies.
098         *
099         * @param subStrategies the collection with sub strategies.
100         * @return {@code this} instance.
101         */
102        public Builder setSubStrategies(final Collection<FileLocationStrategy> subStrategies) {
103            this.subStrategies = subStrategies;
104            return asThis();
105        }
106
107    }
108
109    /** A collection with all sub strategies managed by this object. */
110    private final Collection<FileLocationStrategy> subStrategies;
111
112    /**
113     * Constructs a new instance.
114     *
115     * @param builder How to build the instance.
116     */
117    private CombinedLocationStrategy(final Builder builder) {
118        super(builder);
119        if (builder.subStrategies == null) {
120            throw new IllegalArgumentException("Collection with sub strategies must not be null.");
121        }
122        if (builder.subStrategies.contains(null)) {
123            throw new IllegalArgumentException("Collection with sub strategies contains null entry.");
124        }
125        subStrategies = Collections.unmodifiableCollection(new ArrayList<>(builder.subStrategies));
126    }
127
128    /**
129     * Creates a new instance of {@code CombinedLocationStrategy} and initializes it with the provided sub strategies. The
130     * passed in collection must not be <strong>null</strong> or contain <strong>null</strong> elements.
131     *
132     * @param subs the collection with sub strategies.
133     * @throws IllegalArgumentException if the collection is <strong>null</strong> or has <strong>null</strong> elements.
134     */
135    public CombinedLocationStrategy(final Collection<FileLocationStrategy> subs) {
136        this(new Builder().setSubStrategies(subs));
137    }
138
139    /**
140     * Gets a (unmodifiable) collection with the sub strategies managed by this object.
141     *
142     * @return the sub {@code FileLocationStrategy} objects
143     */
144    public Collection<FileLocationStrategy> getSubStrategies() {
145        return subStrategies;
146    }
147
148    /**
149     * {@inheritDoc} This implementation tries to locate the file by delegating to the managed sub strategies.
150     */
151    @Override
152    public URL locate(final FileSystem fileSystem, final FileLocator locator) {
153        for (final FileLocationStrategy sub : getSubStrategies()) {
154            final URL url = sub.locate(fileSystem, locator);
155            if (url != null) {
156                return check(url);
157            }
158        }
159        return null;
160    }
161}