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;
032
033/**
034 * Provides utility methods for working with resources in the classpath. Note that even though these
035 * methods use {@link URL} parameters, they are usually not appropriate for HTTP or other
036 * non-classpath resources.
037 *
038 * <p>All method parameters must be non-null unless documented otherwise.
039 *
040 * @author Chris Nokleberg
041 * @author Ben Yu
042 * @author Colin Decker
043 * @since 1.0
044 */
045@Beta
046@GwtIncompatible
047public final class Resources {
048  private Resources() {}
049
050  /**
051   * Returns a {@link ByteSource} that reads from the given URL.
052   *
053   * @since 14.0
054   */
055  public static ByteSource asByteSource(URL url) {
056    return new UrlByteSource(url);
057  }
058
059  /**
060   * A byte source that reads from a URL using {@link URL#openStream()}.
061   */
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  public static <T> T readLines(URL url, Charset charset, LineProcessor<T> callback)
127      throws IOException {
128    return asCharSource(url, charset).readLines(callback);
129  }
130
131  /**
132   * Reads all of the lines from a URL. The lines do not include line-termination characters, but do
133   * include other leading and trailing whitespace.
134   *
135   * <p>This method returns a mutable {@code List}. For an {@code ImmutableList}, use
136   * {@code Resources.asCharSource(url, charset).readLines()}.
137   *
138   * @param url the URL to read from
139   * @param charset the charset used to decode the input stream; see {@link Charsets} for helpful
140   *     predefined constants
141   * @return a mutable {@link List} containing all the lines
142   * @throws IOException if an I/O error occurs
143   */
144  public static List<String> readLines(URL url, Charset charset) throws IOException {
145    // don't use asCharSource(url, charset).readLines() because that returns
146    // an immutable list, which would change the behavior of this method
147    return readLines(
148        url,
149        charset,
150        new LineProcessor<List<String>>() {
151          final List<String> result = Lists.newArrayList();
152
153          @Override
154          public boolean processLine(String line) {
155            result.add(line);
156            return true;
157          }
158
159          @Override
160          public List<String> getResult() {
161            return result;
162          }
163        });
164  }
165
166  /**
167   * Copies all bytes from a URL to an output stream.
168   *
169   * @param from the URL to read from
170   * @param to the output stream
171   * @throws IOException if an I/O error occurs
172   */
173  public static void copy(URL from, OutputStream to) throws IOException {
174    asByteSource(from).copyTo(to);
175  }
176
177  /**
178   * Returns a {@code URL} pointing to {@code resourceName} if the resource is found using the
179   * {@linkplain Thread#getContextClassLoader() context class loader}. In simple environments, the
180   * context class loader will find resources from the class path. In environments where different
181   * threads can have different class loaders, for example app servers, the context class loader
182   * will typically have been set to an appropriate loader for the current thread.
183   *
184   * <p>In the unusual case where the context class loader is null, the class loader that loaded
185   * this class ({@code Resources}) will be used instead.
186   *
187   * @throws IllegalArgumentException if the resource is not found
188   */
189  @CanIgnoreReturnValue // being used to check if a resource exists
190  // TODO(cgdecker): maybe add a better way to check if a resource exists
191  // e.g. Optional<URL> tryGetResource or boolean resourceExists
192  public static URL getResource(String resourceName) {
193    ClassLoader loader =
194        MoreObjects.firstNonNull(
195            Thread.currentThread().getContextClassLoader(), Resources.class.getClassLoader());
196    URL url = loader.getResource(resourceName);
197    checkArgument(url != null, "resource %s not found.", resourceName);
198    return url;
199  }
200
201  /**
202   * Given a {@code resourceName} that is relative to {@code contextClass}, returns a {@code URL}
203   * pointing to the named resource.
204   *
205   * @throws IllegalArgumentException if the resource is not found
206   */
207  public static URL getResource(Class<?> contextClass, String resourceName) {
208    URL url = contextClass.getResource(resourceName);
209    checkArgument(
210        url != null, "resource %s relative to %s not found.", resourceName, contextClass.getName());
211    return url;
212  }
213}