001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. 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 distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.io;
016
017import static com.google.common.base.Preconditions.checkArgument;
018import static com.google.common.base.Preconditions.checkNotNull;
019
020import com.google.common.annotations.Beta;
021import com.google.common.annotations.GwtIncompatible;
022import com.google.common.base.Charsets;
023import com.google.common.base.MoreObjects;
024import com.google.common.collect.Lists;
025import com.google.errorprone.annotations.CanIgnoreReturnValue;
026import java.io.IOException;
027import java.io.InputStream;
028import java.io.OutputStream;
029import java.net.URL;
030import java.nio.charset.Charset;
031import java.util.List;
032import org.checkerframework.checker.nullness.qual.Nullable;
033
034/**
035 * Provides utility methods for working with resources in the classpath. Note that even though these
036 * methods use {@link URL} parameters, they are usually not appropriate for HTTP or other
037 * non-classpath resources.
038 *
039 * <p>All method parameters must be non-null unless documented otherwise.
040 *
041 * @author Chris Nokleberg
042 * @author Ben Yu
043 * @author Colin Decker
044 * @since 1.0
045 */
046@Beta
047@GwtIncompatible
048@ElementTypesAreNonnullByDefault
049public final class Resources {
050  private Resources() {}
051
052  /**
053   * Returns a {@link ByteSource} that reads from the given URL.
054   *
055   * @since 14.0
056   */
057  public static ByteSource asByteSource(URL url) {
058    return new UrlByteSource(url);
059  }
060
061  /** A byte source that reads from a URL using {@link URL#openStream()}. */
062  private static final class UrlByteSource extends ByteSource {
063
064    private final URL url;
065
066    private UrlByteSource(URL url) {
067      this.url = checkNotNull(url);
068    }
069
070    @Override
071    public InputStream openStream() throws IOException {
072      return url.openStream();
073    }
074
075    @Override
076    public String toString() {
077      return "Resources.asByteSource(" + url + ")";
078    }
079  }
080
081  /**
082   * Returns a {@link CharSource} that reads from the given URL using the given character set.
083   *
084   * @since 14.0
085   */
086  public static CharSource asCharSource(URL url, Charset charset) {
087    return asByteSource(url).asCharSource(charset);
088  }
089
090  /**
091   * Reads all bytes from a URL into a byte array.
092   *
093   * @param url the URL to read from
094   * @return a byte array containing all the bytes from the URL
095   * @throws IOException if an I/O error occurs
096   */
097  public static byte[] toByteArray(URL url) throws IOException {
098    return asByteSource(url).read();
099  }
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}