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 *     http://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.net.URL;
020
021/**
022 * <p>
023 * An interface allowing applications to customize the process of locating a
024 * file.
025 * </p>
026 * <p>
027 * {@link FileHandler} uses {@link FileLocator} objects for referencing files.
028 * These objects are not guaranteed to identify a file in a unique way. For
029 * instance, if only a file name is defined, this could mean a relative file
030 * name in the current directory, the name of a resource to be loaded from the
031 * class path, or something else. Before the file described by a
032 * {@code FileLocator} can be actually accessed, an unambiguous URL pointing to
033 * this file has to be obtained. This is the job of a
034 * {@code FileLocationStrategy}.
035 * </p>
036 * <p>
037 * This interface defines a method for locating a file provided as a
038 * {@code FileLocator} object. If location is successful, a URL is returned. A
039 * concrete implementation can perform arbitrary actions to search for the file
040 * in question at various places. There will also be an implementation allowing
041 * the combination of multiple {@code FileLocationStrategy} implementations; so
042 * a file can be searched using multiple strategies until one of them is
043 * successful.
044 * </p>
045 *
046 * @since 2.0
047 */
048public interface FileLocationStrategy
049{
050    /**
051     * Tries to locate the specified file. The method also expects the
052     * {@code FileSystem} to be used. Note that the {@code FileLocator} object
053     * may also contain a {@code FileSystem}, but this is optional. The passed
054     * in {@code FileSystem} should be used, and callers must not pass a
055     * <b>null</b> reference for this argument. A concrete implementation has to
056     * evaluate the properties stored in the {@code FileLocator} object and try
057     * to match them to an existing file. If this can be done, a corresponding
058     * URL is returned. Otherwise, result is <b>null</b>. Implementations should
059     * not throw an exception (unless parameters are <b>null</b>) as there might
060     * be alternative strategies which can find the file in question.
061     *
062     * @param fileSystem the {@code FileSystem} to be used for this operation
063     * @param locator the object describing the file to be located
064     * @return a URL pointing to the referenced file if location was successful;
065     *         <b>null</b> if the file could not be resolved
066     */
067    URL locate(FileSystem fileSystem, FileLocator locator);
068}