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.List;
025import java.util.Set;
026import java.util.regex.Pattern;
027
028/**
029 * A specialized implementation of a {@code FileLocationStrategy} which encapsulates an arbitrary number of
030 * {@code FileLocationStrategy} objects.
031 * <p>
032 * A collection with the wrapped {@code FileLocationStrategy} objects is passed at construction time. During a
033 * [{@code locate()} operation the wrapped strategies are called one after the other until one returns a non <strong>null</strong>
034 * URL. This URL is returned. If none of the wrapped strategies is able to resolve the passed in {@link FileLocator},
035 * result is <strong>null</strong>. This is similar to the <em>chain of responsibility</em> design pattern.
036 * </p>
037 * <p>
038 * This class, together with the provided concrete {@code FileLocationStrategy} implementations, offers a convenient way
039 * to customize the lookup for configuration files: Just add the desired concrete strategies to a
040 * {@code CombinedLocationStrategy} object. If necessary, custom strategies can be implemented if there are specific
041 * requirements. Note that the order in which strategies are added to a {@code CombinedLocationStrategy} matters: sub
042 * strategies are queried in the same order as they appear in the collection passed to the constructor.
043 * </p>
044 * <p>
045 * See {@link AbstractFileLocationStrategy} learn how to grant an deny URL schemes and hosts.
046 * </p>
047 *
048 * @see AbstractFileLocationStrategy
049 * @since 2.0
050 */
051public class CombinedLocationStrategy extends AbstractFileLocationStrategy {
052
053    /**
054     * Builds new instances of {@link CombinedLocationStrategy}.
055     *
056     * @since 2.15.0
057     */
058    public static class Builder extends AbstractBuilder<CombinedLocationStrategy, Builder> {
059
060        /** A collection with all sub strategies managed by this object. */
061        private Collection<? extends FileLocationStrategy> subStrategies;
062
063        /**
064         * Constructs a new instance.
065         */
066        public Builder() {
067            // empty
068        }
069
070        @Override
071        public CombinedLocationStrategy get() throws IOException {
072            return new CombinedLocationStrategy(this);
073        }
074
075        /**
076         * Propagates properties of the parent builder scheme and host to subStrategies.
077         *
078         * @return {@code this} instance.
079         */
080        public Builder propagate() {
081            if (subStrategies != null) {
082                subStrategies.forEach(e -> {
083                    if (e instanceof AbstractFileLocationStrategy) {
084                        final AbstractFileLocationStrategy afls = (AbstractFileLocationStrategy) e;
085                        final Set<String> schemes = afls.getSchemes();
086                        schemes.clear();
087                        schemes.addAll(getSchemes());
088                        final Set<Pattern> hosts = afls.getHosts();
089                        hosts.clear();
090                        hosts.addAll(getHosts());
091                    }
092                });
093            }
094            return asThis();
095        }
096
097        /**
098         * Sets the collection with sub strategies.
099         *
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}