1 /*
2 * Copyright (C) 2007 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
5 * in compliance with the License. You may obtain a copy of the License at
6 *
7 * http://www.apache.org/licenses/LICENSE-2.0
8 *
9 * Unless required by applicable law or agreed to in writing, software distributed under the License
10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
11 * or implied. See the License for the specific language governing permissions and limitations under
12 * the License.
13 */
14
15 package com.google.common.io;
16
17 import static com.google.common.base.Preconditions.checkArgument;
18 import static com.google.common.base.Preconditions.checkNotNull;
19
20 import com.google.common.annotations.Beta;
21 import com.google.common.annotations.GwtIncompatible;
22 import com.google.common.base.Charsets;
23 import com.google.common.base.MoreObjects;
24 import com.google.common.collect.Lists;
25 import com.google.errorprone.annotations.CanIgnoreReturnValue;
26 import java.io.IOException;
27 import java.io.InputStream;
28 import java.io.OutputStream;
29 import java.net.URL;
30 import java.nio.charset.Charset;
31 import java.util.List;
32 import org.checkerframework.checker.nullness.qual.Nullable;
33
34 /**
35 * Provides utility methods for working with resources in the classpath. Note that even though these
36 * methods use {@link URL} parameters, they are usually not appropriate for HTTP or other
37 * non-classpath resources.
38 *
39 * <p>All method parameters must be non-null unless documented otherwise.
40 *
41 * @author Chris Nokleberg
42 * @author Ben Yu
43 * @author Colin Decker
44 * @since 1.0
45 */
46 @Beta
47 @GwtIncompatible
48 @ElementTypesAreNonnullByDefault
49 public final class Resources {
50 private Resources() {}
51
52 /**
53 * Returns a {@link ByteSource} that reads from the given URL.
54 *
55 * @since 14.0
56 */
57 public static ByteSource asByteSource(URL url) {
58 return new UrlByteSource(url);
59 }
60
61 /** A byte source that reads from a URL using {@link URL#openStream()}. */
62 private static final class UrlByteSource extends ByteSource {
63
64 private final URL url;
65
66 private UrlByteSource(URL url) {
67 this.url = checkNotNull(url);
68 }
69
70 @Override
71 public InputStream openStream() throws IOException {
72 return url.openStream();
73 }
74
75 @Override
76 public String toString() {
77 return "Resources.asByteSource(" + url + ")";
78 }
79 }
80
81 /**
82 * Returns a {@link CharSource} that reads from the given URL using the given character set.
83 *
84 * @since 14.0
85 */
86 public static CharSource asCharSource(URL url, Charset charset) {
87 return asByteSource(url).asCharSource(charset);
88 }
89
90 /**
91 * Reads all bytes from a URL into a byte array.
92 *
93 * @param url the URL to read from
94 * @return a byte array containing all the bytes from the URL
95 * @throws IOException if an I/O error occurs
96 */
97 public static byte[] toByteArray(URL url) throws IOException {
98 return asByteSource(url).read();
99 }
100
101 /**
102 * Reads all characters from a URL into a {@link String}, using the given character set.
103 *
104 * @param url the URL to read from
105 * @param charset the charset used to decode the input stream; see {@link Charsets} for helpful
106 * predefined constants
107 * @return a string containing all the characters from the URL
108 * @throws IOException if an I/O error occurs.
109 */
110 public static String toString(URL url, Charset charset) throws IOException {
111 return asCharSource(url, charset).read();
112 }
113
114 /**
115 * Streams lines from a URL, stopping when our callback returns false, or we have read all of the
116 * lines.
117 *
118 * @param url the URL to read from
119 * @param charset the charset used to decode the input stream; see {@link Charsets} for helpful
120 * predefined constants
121 * @param callback the LineProcessor to use to handle the lines
122 * @return the output of processing the lines
123 * @throws IOException if an I/O error occurs
124 */
125 @CanIgnoreReturnValue // some processors won't return a useful result
126 @ParametricNullness
127 public static <T extends @Nullable Object> T readLines(
128 URL url, Charset charset, LineProcessor<T> callback) throws IOException {
129 return asCharSource(url, charset).readLines(callback);
130 }
131
132 /**
133 * Reads all of the lines from a URL. The lines do not include line-termination characters, but do
134 * include other leading and trailing whitespace.
135 *
136 * <p>This method returns a mutable {@code List}. For an {@code ImmutableList}, use {@code
137 * Resources.asCharSource(url, charset).readLines()}.
138 *
139 * @param url the URL to read from
140 * @param charset the charset used to decode the input stream; see {@link Charsets} for helpful
141 * predefined constants
142 * @return a mutable {@link List} containing all the lines
143 * @throws IOException if an I/O error occurs
144 */
145 public static List<String> readLines(URL url, Charset charset) throws IOException {
146 // don't use asCharSource(url, charset).readLines() because that returns
147 // an immutable list, which would change the behavior of this method
148 return readLines(
149 url,
150 charset,
151 new LineProcessor<List<String>>() {
152 final List<String> result = Lists.newArrayList();
153
154 @Override
155 public boolean processLine(String line) {
156 result.add(line);
157 return true;
158 }
159
160 @Override
161 public List<String> getResult() {
162 return result;
163 }
164 });
165 }
166
167 /**
168 * Copies all bytes from a URL to an output stream.
169 *
170 * @param from the URL to read from
171 * @param to the output stream
172 * @throws IOException if an I/O error occurs
173 */
174 public static void copy(URL from, OutputStream to) throws IOException {
175 asByteSource(from).copyTo(to);
176 }
177
178 /**
179 * Returns a {@code URL} pointing to {@code resourceName} if the resource is found using the
180 * {@linkplain Thread#getContextClassLoader() context class loader}. In simple environments, the
181 * context class loader will find resources from the class path. In environments where different
182 * threads can have different class loaders, for example app servers, the context class loader
183 * will typically have been set to an appropriate loader for the current thread.
184 *
185 * <p>In the unusual case where the context class loader is null, the class loader that loaded
186 * this class ({@code Resources}) will be used instead.
187 *
188 * @throws IllegalArgumentException if the resource is not found
189 */
190 @CanIgnoreReturnValue // being used to check if a resource exists
191 // TODO(cgdecker): maybe add a better way to check if a resource exists
192 // e.g. Optional<URL> tryGetResource or boolean resourceExists
193 public static URL getResource(String resourceName) {
194 ClassLoader loader =
195 MoreObjects.firstNonNull(
196 Thread.currentThread().getContextClassLoader(), Resources.class.getClassLoader());
197 URL url = loader.getResource(resourceName);
198 checkArgument(url != null, "resource %s not found.", resourceName);
199 return url;
200 }
201
202 /**
203 * Given a {@code resourceName} that is relative to {@code contextClass}, returns a {@code URL}
204 * pointing to the named resource.
205 *
206 * @throws IllegalArgumentException if the resource is not found
207 */
208 @CanIgnoreReturnValue // being used to check if a resource exists
209 public static URL getResource(Class<?> contextClass, String resourceName) {
210 URL url = contextClass.getResource(resourceName);
211 checkArgument(
212 url != null, "resource %s relative to %s not found.", resourceName, contextClass.getName());
213 return url;
214 }
215 }