001// Licensed under the Apache License, Version 2.0 (the "License");
002// you may not use this file except in compliance with the License.
003// You may obtain a copy of the License at
004//
005//     http://www.apache.org/licenses/LICENSE-2.0
006//
007// Unless required by applicable law or agreed to in writing, software
008// distributed under the License is distributed on an "AS IS" BASIS,
009// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
010// See the License for the specific language governing permissions and
011// limitations under the License.
012
013package org.apache.tapestry5.ioc;
014
015import java.io.IOException;
016import java.io.InputStream;
017import java.net.URL;
018import java.util.Locale;
019
020/**
021 * Represents a resource on the server that may be used for server side processing, or may be exposed to the client
022 * side. Generally, this represents an abstraction on top of files on the class path and files stored in the web
023 * application context.
024 * <p/>
025 * Resources are often used as map keys; they should be immutable and should implement hashCode() and equals().
026 */
027public interface Resource
028{
029
030    /**
031     * Returns true if the resource exists; if a stream to the content of the file may be opened. A resource exists
032     * if {@link #toURL()} returns a non-null value. Starting in release 5.3.4, the result of this is cached.
033     * <p/>
034     * Starting in 5.4, some "virtual resources", may return true even though {@link #toURL()} returns null.
035     *
036     * @return true if the resource exists, false if it does not
037     */
038    boolean exists();
039
040
041    /**
042     * Returns true if the resource is virtual, meaning this is no underlying file. Many operations are unsupported
043     * on virtual resources, including {@link #toURL()}, {@link #forLocale(java.util.Locale)},
044     * {@link #withExtension(String)}, {@link #getFile()}, {@link #getFolder()}, {@link #getPath()}}; these
045     * operations will throw an {@link java.lang.UnsupportedOperationException}.
046     *
047     * @since 5.4
048     */
049    boolean isVirtual();
050
051    /**
052     * Opens a stream to the content of the resource, or returns null if the resource does not exist. The native
053     * input stream supplied by the resource is wrapped in a {@link java.io.BufferedInputStream}.
054     *
055     * @return an open, buffered stream to the content, if available
056     */
057    InputStream openStream() throws IOException;
058
059    /**
060     * 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
061     * the result.  Starting in 5.4, some "virtual resources" may return null.
062     */
063    URL toURL();
064
065    /**
066     * Returns a localized version of the resource. May return null if no such resource exists. Starting in release
067     * 5.3.4, the result of this method is cached internally.
068     */
069    Resource forLocale(Locale locale);
070
071    /**
072     * Returns a Resource based on a relative path, relative to the folder containing the resource. Understands the "."
073     * (current folder) and ".." (parent folder) conventions, and treats multiple sequential slashes as a single slash.
074     * <p/>
075     * Virtual resources (resources fabricated at runtime) return themselves.
076     */
077    Resource forFile(String relativePath);
078
079    /**
080     * Returns a new Resource with the extension changed (or, if the resource does not have an extension, the extension
081     * is added). The new Resource may not exist (that is, {@link #toURL()} may return null.
082     *
083     * @param extension
084     *         to apply to the resource, such as "html" or "properties"
085     * @return the new resource
086     */
087    Resource withExtension(String extension);
088
089    /**
090     * Returns the portion of the path up to the last forward slash; this is the directory or folder portion of the
091     * Resource.
092     */
093    String getFolder();
094
095    /**
096     * Returns the file portion of the Resource path, everything that follows the final forward slash.
097     * <p/>
098     * Starting in 5.4, certain kinds of "virtual resources" may return null here.
099     */
100    String getFile();
101
102    /**
103     * Return the path (the combination of folder and file).
104     * <p/>
105     * Starting in 5.4, certain "virtual resources", may return an arbitrary value here.
106     */
107    String getPath();
108}