1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.configuration2.io;
18
19 import java.net.URL;
20
21 /**
22 * <p>
23 * An interface allowing applications to customize the process of locating a file.
24 * </p>
25 * <p>
26 * {@link FileHandler} uses {@link FileLocator} objects for referencing files. These objects are not guaranteed to
27 * identify a file in a unique way. For instance, if only a file name is defined, this could mean a relative file name
28 * in the current directory, the name of a resource to be loaded from the class path, or something else. Before the file
29 * described by a {@code FileLocator} can be actually accessed, an unambiguous URL pointing to this file has to be
30 * obtained. This is the job of a {@code FileLocationStrategy}.
31 * </p>
32 * <p>
33 * This interface defines a method for locating a file provided as a {@code FileLocator} object. If location is
34 * successful, a URL is returned. A concrete implementation can perform arbitrary actions to search for the file in
35 * question at various places. There will also be an implementation allowing the combination of multiple
36 * {@code FileLocationStrategy} implementations; so a file can be searched using multiple strategies until one of them
37 * is successful.
38 * </p>
39 *
40 * @since 2.0
41 */
42 public interface FileLocationStrategy {
43 /**
44 * Tries to locate the specified file. The method also expects the {@code FileSystem} to be used. Note that the
45 * {@code FileLocator} object may also contain a {@code FileSystem}, but this is optional. The passed in
46 * {@code FileSystem} should be used, and callers must not pass a <b>null</b> reference for this argument. A concrete
47 * implementation has to evaluate the properties stored in the {@code FileLocator} object and try to match them to an
48 * existing file. If this can be done, a corresponding URL is returned. Otherwise, result is <b>null</b>.
49 * Implementations should not throw an exception (unless parameters are <b>null</b>) as there might be alternative
50 * strategies which can find the file in question.
51 *
52 * @param fileSystem the {@code FileSystem} to be used for this operation
53 * @param locator the object describing the file to be located
54 * @return a URL pointing to the referenced file if location was successful; <b>null</b> if the file could not be
55 * resolved
56 */
57 URL locate(FileSystem fileSystem, FileLocator locator);
58 }