    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}