001/*
002 * Copyright 2002-2018 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.core.io;
018
019import java.io.File;
020import java.io.IOException;
021import java.io.InputStream;
022import java.net.URI;
023import java.net.URL;
024import java.nio.channels.Channels;
025import java.nio.channels.ReadableByteChannel;
026
027import org.springframework.lang.Nullable;
028
029/**
030 * Interface for a resource descriptor that abstracts from the actual
031 * type of underlying resource, such as a file or class path resource.
032 *
033 * <p>An InputStream can be opened for every resource if it exists in
034 * physical form, but a URL or File handle can just be returned for
035 * certain resources. The actual behavior is implementation-specific.
036 *
037 * @author Juergen Hoeller
038 * @since 28.12.2003
039 * @see #getInputStream()
040 * @see #getURL()
041 * @see #getURI()
042 * @see #getFile()
043 * @see WritableResource
044 * @see ContextResource
045 * @see UrlResource
046 * @see FileUrlResource
047 * @see FileSystemResource
048 * @see ClassPathResource
049 * @see ByteArrayResource
050 * @see InputStreamResource
051 */
052public interface Resource extends InputStreamSource {
053
054        /**
055         * Determine whether this resource actually exists in physical form.
056         * <p>This method performs a definitive existence check, whereas the
057         * existence of a {@code Resource} handle only guarantees a valid
058         * descriptor handle.
059         */
060        boolean exists();
061
062        /**
063         * Indicate whether non-empty contents of this resource can be read via
064         * {@link #getInputStream()}.
065         * <p>Will be {@code true} for typical resource descriptors that exist
066         * since it strictly implies {@link #exists()} semantics as of 5.1.
067         * Note that actual content reading may still fail when attempted.
068         * However, a value of {@code false} is a definitive indication
069         * that the resource content cannot be read.
070         * @see #getInputStream()
071         * @see #exists()
072         */
073        default boolean isReadable() {
074                return exists();
075        }
076
077        /**
078         * Indicate whether this resource represents a handle with an open stream.
079         * If {@code true}, the InputStream cannot be read multiple times,
080         * and must be read and closed to avoid resource leaks.
081         * <p>Will be {@code false} for typical resource descriptors.
082         */
083        default boolean isOpen() {
084                return false;
085        }
086
087        /**
088         * Determine whether this resource represents a file in a file system.
089         * A value of {@code true} strongly suggests (but does not guarantee)
090         * that a {@link #getFile()} call will succeed.
091         * <p>This is conservatively {@code false} by default.
092         * @since 5.0
093         * @see #getFile()
094         */
095        default boolean isFile() {
096                return false;
097        }
098
099        /**
100         * Return a URL handle for this resource.
101         * @throws IOException if the resource cannot be resolved as URL,
102         * i.e. if the resource is not available as descriptor
103         */
104        URL getURL() throws IOException;
105
106        /**
107         * Return a URI handle for this resource.
108         * @throws IOException if the resource cannot be resolved as URI,
109         * i.e. if the resource is not available as descriptor
110         * @since 2.5
111         */
112        URI getURI() throws IOException;
113
114        /**
115         * Return a File handle for this resource.
116         * @throws java.io.FileNotFoundException if the resource cannot be resolved as
117         * absolute file path, i.e. if the resource is not available in a file system
118         * @throws IOException in case of general resolution/reading failures
119         * @see #getInputStream()
120         */
121        File getFile() throws IOException;
122
123        /**
124         * Return a {@link ReadableByteChannel}.
125         * <p>It is expected that each call creates a <i>fresh</i> channel.
126         * <p>The default implementation returns {@link Channels#newChannel(InputStream)}
127         * with the result of {@link #getInputStream()}.
128         * @return the byte channel for the underlying resource (must not be {@code null})
129         * @throws java.io.FileNotFoundException if the underlying resource doesn't exist
130         * @throws IOException if the content channel could not be opened
131         * @since 5.0
132         * @see #getInputStream()
133         */
134        default ReadableByteChannel readableChannel() throws IOException {
135                return Channels.newChannel(getInputStream());
136        }
137
138        /**
139         * Determine the content length for this resource.
140         * @throws IOException if the resource cannot be resolved
141         * (in the file system or as some other known physical resource type)
142         */
143        long contentLength() throws IOException;
144
145        /**
146         * Determine the last-modified timestamp for this resource.
147         * @throws IOException if the resource cannot be resolved
148         * (in the file system or as some other known physical resource type)
149         */
150        long lastModified() throws IOException;
151
152        /**
153         * Create a resource relative to this resource.
154         * @param relativePath the relative path (relative to this resource)
155         * @return the resource handle for the relative resource
156         * @throws IOException if the relative resource cannot be determined
157         */
158        Resource createRelative(String relativePath) throws IOException;
159
160        /**
161         * Determine a filename for this resource, i.e. typically the last
162         * part of the path: for example, "myfile.txt".
163         * <p>Returns {@code null} if this type of resource does not
164         * have a filename.
165         */
166        @Nullable
167        String getFilename();
168
169        /**
170         * Return a description for this resource,
171         * to be used for error output when working with the resource.
172         * <p>Implementations are also encouraged to return this value
173         * from their {@code toString} method.
174         * @see Object#toString()
175         */
176        String getDescription();
177
178}