001// Copyright 2006, 2008, 2012 The Apache Software Foundation
002//
003// Licensed under the Apache License, Version 2.0 (the "License");
004// you may not use this file except in compliance with the License.
005// You may obtain a copy of the License at
006//
007//     http://www.apache.org/licenses/LICENSE-2.0
008//
009// Unless required by applicable law or agreed to in writing, software
010// distributed under the License is distributed on an "AS IS" BASIS,
011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012// See the License for the specific language governing permissions and
013// limitations under the License.
014
015package org.apache.tapestry5.ioc;
016
017import java.io.IOException;
018import java.io.InputStream;
019import java.net.URL;
020import java.util.Locale;
021
022/**
023 * Represents a resource on the server that may be used for server side processing, or may be exposed to the client
024 * side. Generally, this represents an abstraction on top of files on the class path and files stored in the web
025 * application context.
026 * <p/>
027 * Resources are often used as map keys; they should be immutable and should implement hashCode() and equals().
028 */
029public interface Resource
030{
031
032    /**
033     * Returns true if the resource exists; if a stream to the content of the file may be opened. A resource exists
034     * if {@link #toURL()} returns a non-null value. Starting in release 5.3.4, the result of this is cached.
035     *
036     * @return true if the resource exists, false if it does not
037     */
038    boolean exists();
039
040    /**
041     * Opens a stream to the content of the resource, or returns null if the resource does not exist.
042     *
043     * @return an open, buffered stream to the content, if available
044     */
045    InputStream openStream() throws IOException;
046
047    /**
048     * Returns the URL for the resource, or null if it does not exist. This value is lazily computed; starting in 5.3.4, subclasses may cache
049     * the result.
050     */
051    URL toURL();
052
053    /**
054     * Returns a localized version of the resource. May return null if no such resource exists. Starting in release
055     * 5.3.4, the result of this method is cached internally.
056     */
057    Resource forLocale(Locale locale);
058
059    /**
060     * Returns a Resource based on a relative path, relative to the folder containing the resource. Understands the "."
061     * (current folder) and ".." (parent folder) conventions, and treats multiple sequential slashes as a single slash.
062     */
063    Resource forFile(String relativePath);
064
065    /**
066     * Returns a new Resource with the extension changed (or, if the resource does not have an extension, the extension
067     * is added). The new Resource may not exist (that is, {@link #toURL()} may return null.
068     *
069     * @param extension
070     *         to apply to the resource, such as "html" or "properties"
071     * @return the new resource
072     */
073    Resource withExtension(String extension);
074
075    /**
076     * Returns the portion of the path up to the last forward slash; this is the directory or folder portion of the
077     * Resource.
078     */
079    String getFolder();
080
081    /**
082     * Returns the file portion of the Resource path, everything that follows the final forward slash.
083     */
084    String getFile();
085
086    /**
087     * Return the path (the combination of folder and file).
088     */
089    String getPath();
090}