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     * <p/>
036     * Starting in 5.4, some "virtual resources", may return true even though {@link #toURL()} returns null.
037     *
038     * @return true if the resource exists, false if it does not
039     */
040    boolean exists();
041
042    /**
043     * Opens a stream to the content of the resource, or returns null if the resource does not exist. The native
044     * input stream supplied by the resource is wrapped in a {@link java.io.BufferedInputStream}.
045     *
046     * @return an open, buffered stream to the content, if available
047     */
048    InputStream openStream() throws IOException;
049
050    /**
051     * 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
052     * the result.  Starting in 5.4, some "virtual resources" may return null.
053     */
054    URL toURL();
055
056    /**
057     * Returns a localized version of the resource. May return null if no such resource exists. Starting in release
058     * 5.3.4, the result of this method is cached internally.
059     */
060    Resource forLocale(Locale locale);
061
062    /**
063     * Returns a Resource based on a relative path, relative to the folder containing the resource. Understands the "."
064     * (current folder) and ".." (parent folder) conventions, and treats multiple sequential slashes as a single slash.
065     * <p/>
066     * Virtual resources (resources fabricated at runtime) return themselves.
067     */
068    Resource forFile(String relativePath);
069
070    /**
071     * Returns a new Resource with the extension changed (or, if the resource does not have an extension, the extension
072     * is added). The new Resource may not exist (that is, {@link #toURL()} may return null.
073     *
074     * @param extension
075     *         to apply to the resource, such as "html" or "properties"
076     * @return the new resource
077     */
078    Resource withExtension(String extension);
079
080    /**
081     * Returns the portion of the path up to the last forward slash; this is the directory or folder portion of the
082     * Resource.
083     */
084    String getFolder();
085
086    /**
087     * Returns the file portion of the Resource path, everything that follows the final forward slash.
088     * <p/>
089     * Starting in 5.4, certain kinds of "virtual resources" may return null here.
090     */
091    String getFile();
092
093    /**
094     * Return the path (the combination of folder and file).
095     * <p/>
096     * Starting in 5.4, certain "virtual resources", may return an arbitrary value here.
097     */
098    String getPath();
099}