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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.configuration2.io;
import java.net.URL;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
/**
*
* A specialized implementation of a {@code FileLocationStrategy} which encapsulates an arbitrary number of
* {@code FileLocationStrategy} objects.
*
*
* A collection with the wrapped {@code FileLocationStrategy} objects is passed at construction time. During a
* [{@code locate()} operation the wrapped strategies are called one after the other until one returns a non null
* URL. This URL is returned. If none of the wrapped strategies is able to resolve the passed in {@link FileLocator},
* result is null. This is similar to the chain of responsibility design pattern.
*
*
* This class, together with the provided concrete {@code FileLocationStrategy} implementations, offers a convenient way
* to customize the lookup for configuration files: Just add the desired concrete strategies to a
* {@code CombinedLocationStrategy} object. If necessary, custom strategies can be implemented if there are specific
* requirements. Note that the order in which strategies are added to a {@code CombinedLocationStrategy} matters: sub
* strategies are queried in the same order as they appear in the collection passed to the constructor.
*
*
* @since 2.0
*/
public class CombinedLocationStrategy implements FileLocationStrategy {
/** A collection with all sub strategies managed by this object. */
private final Collection subStrategies;
/**
* Creates a new instance of {@code CombinedLocationStrategy} and initializes it with the provided sub strategies. The
* passed in collection must not be null or contain null elements.
*
* @param subs the collection with sub strategies
* @throws IllegalArgumentException if the collection is null or has null elements
*/
public CombinedLocationStrategy(final Collection subs) {
if (subs == null) {
throw new IllegalArgumentException("Collection with sub strategies must not be null!");
}
subStrategies = Collections.unmodifiableCollection(new ArrayList<>(subs));
if (subStrategies.contains(null)) {
throw new IllegalArgumentException("Collection with sub strategies contains null entry!");
}
}
/**
* Gets a (unmodifiable) collection with the sub strategies managed by this object.
*
* @return the sub {@code FileLocationStrategy} objects
*/
public Collection getSubStrategies() {
return subStrategies;
}
/**
* {@inheritDoc} This implementation tries to locate the file by delegating to the managed sub strategies.
*/
@Override
public URL locate(final FileSystem fileSystem, final FileLocator locator) {
for (final FileLocationStrategy sub : getSubStrategies()) {
final URL url = sub.locate(fileSystem, locator);
if (url != null) {
return url;
}
}
return null;
}
}