001/*
002 * Copyright (C) 2007 The Guava 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 * http://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 com.google.common.io;
018
019import static com.google.common.base.Preconditions.checkArgument;
020import static com.google.common.base.Preconditions.checkNotNull;
021
022import com.google.common.annotations.Beta;
023
024import java.io.IOException;
025import java.io.InputStream;
026import java.io.InputStreamReader;
027import java.io.OutputStream;
028import java.net.URL;
029import java.nio.charset.Charset;
030import java.util.List;
031
032/**
033 * Provides utility methods for working with resources in the classpath.
034 * Note that even though these methods use {@link URL} parameters, they
035 * are usually not appropriate for HTTP or other non-classpath resources.
036 *
037 * <p>All method parameters must be non-null unless documented otherwise.
038 *
039 * @author Chris Nokleberg
040 * @author Ben Yu
041 * @since 1
042 */
043@Beta
044public final class Resources {
045  private Resources() {}
046
047  /**
048   * Returns a factory that will supply instances of {@link InputStream} that
049   * read from the given URL.
050   *
051   * @param url the URL to read from
052   * @return the factory
053   */
054  public static InputSupplier<InputStream> newInputStreamSupplier(
055      final URL url) {
056    checkNotNull(url);
057    return new InputSupplier<InputStream>() {
058      @Override
059      public InputStream getInput() throws IOException {
060        return url.openStream();
061      }
062    };
063  }
064
065  /**
066   * Returns a factory that will supply instances of
067   * {@link InputStreamReader} that read a URL using the given character set.
068   *
069   * @param url the URL to read from
070   * @param charset the character set used when reading the URL contents
071   * @return the factory
072   */
073  public static InputSupplier<InputStreamReader> newReaderSupplier(
074      URL url, Charset charset) {
075    return CharStreams.newReaderSupplier(newInputStreamSupplier(url), charset);
076  }
077
078  /**
079   * Reads all bytes from a URL into a byte array.
080   *
081   * @param url the URL to read from
082   * @return a byte array containing all the bytes from the URL
083   * @throws IOException if an I/O error occurs
084   */
085  public static byte[] toByteArray(URL url) throws IOException {
086    return ByteStreams.toByteArray(newInputStreamSupplier(url));
087  }
088
089  /**
090   * Reads all characters from a URL into a {@link String}, using the given
091   * character set.
092   *
093   * @param url the URL to read from
094   * @param charset the character set used when reading the URL
095   * @return a string containing all the characters from the URL
096   * @throws IOException if an I/O error occurs.
097   */
098  public static String toString(URL url, Charset charset) throws IOException {
099    return CharStreams.toString(newReaderSupplier(url, charset));
100  }
101
102  /**
103   * Streams lines from a URL, stopping when our callback returns false, or we
104   * have read all of the lines.
105   *
106   * @param url the URL to read from
107   * @param charset the character set used when reading the URL
108   * @param callback the LineProcessor to use to handle the lines
109   * @return the output of processing the lines
110   * @throws IOException if an I/O error occurs
111   */
112  public static <T> T readLines(URL url, Charset charset,
113      LineProcessor<T> callback) throws IOException {
114    return CharStreams.readLines(newReaderSupplier(url, charset), callback);
115  }
116
117  /**
118   * Reads all of the lines from a URL. The lines do not include
119   * line-termination characters, but do include other leading and trailing
120   * whitespace.
121   *
122   * @param url the URL to read from
123   * @param charset the character set used when writing the file
124   * @return a mutable {@link List} containing all the lines
125   * @throws IOException if an I/O error occurs
126   */
127  public static List<String> readLines(URL url, Charset charset)
128      throws IOException {
129    return CharStreams.readLines(newReaderSupplier(url, charset));
130  }
131
132  /**
133   * Copies all bytes from a URL to an output stream.
134   *
135   * @param from the URL to read from
136   * @param to the output stream
137   * @throws IOException if an I/O error occurs
138   */
139  public static void copy(URL from, OutputStream to) throws IOException {
140    ByteStreams.copy(newInputStreamSupplier(from), to);
141  }
142  
143  /**
144   * Returns a {@code URL} pointing to {@code resourceName} if the resource is
145   * found in the class path. {@code Resources.class.getClassLoader()} is used
146   * to locate the resource.
147   * 
148   * @throws IllegalArgumentException if resource is not found
149   */
150  public static URL getResource(String resourceName) {
151    URL url = Resources.class.getClassLoader().getResource(resourceName);
152    checkArgument(url != null, "resource %s not found.", resourceName);
153    return url;
154  }
155
156  /**
157   * Returns a {@code URL} pointing to {@code resourceName} that is relative to
158   * {@code contextClass}, if the resource is found in the class path. 
159   * 
160   * @throws IllegalArgumentException if resource is not found
161   */
162  public static URL getResource(Class<?> contextClass, String resourceName) {
163    URL url = contextClass.getResource(resourceName);
164    checkArgument(url != null, "resource %s relative to %s not found.",
165        resourceName, contextClass.getName());
166    return url;
167  }
168}