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/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.io;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import com.google.common.base.Charsets;
import com.google.common.base.MoreObjects;
import com.google.common.collect.Lists;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URL;
import java.nio.charset.Charset;
import java.util.List;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Provides utility methods for working with resources in the classpath. Note that even though these
 * methods use {@link URL} parameters, they are usually not appropriate for HTTP or other
 * non-classpath resources.
 *
 * @author Chris Nokleberg
 * @author Ben Yu
 * @author Colin Decker
 * @since 1.0
 */
@J2ktIncompatible
@GwtIncompatible
@ElementTypesAreNonnullByDefault
public final class Resources {
  private Resources() {}

  /**
   * Returns a {@link ByteSource} that reads from the given URL.
   *
   * @since 14.0
   */
  public static ByteSource asByteSource(URL url) {
    return new UrlByteSource(url);
  }

  /** A byte source that reads from a URL using {@link URL#openStream()}. */
  private static final class UrlByteSource extends ByteSource {

    private final URL url;

    private UrlByteSource(URL url) {
      this.url = checkNotNull(url);
    }

    @Override
    public InputStream openStream() throws IOException {
      return url.openStream();
    }

    @Override
    public String toString() {
      return "Resources.asByteSource(" + url + ")";
    }
  }

  /**
   * Returns a {@link CharSource} that reads from the given URL using the given character set.
   *
   * @since 14.0
   */
  public static CharSource asCharSource(URL url, Charset charset) {
    return asByteSource(url).asCharSource(charset);
  }

  /**
   * Reads all bytes from a URL into a byte array.
   *
   * @param url the URL to read from
   * @return a byte array containing all the bytes from the URL
   * @throws IOException if an I/O error occurs
   */
  public static byte[] toByteArray(URL url) throws IOException {
    return asByteSource(url).read();
  }

  /**
   * Reads all characters from a URL into a {@link String}, using the given character set.
   *
   * @param url the URL to read from
   * @param charset the charset used to decode the input stream; see {@link Charsets} for helpful
   *     predefined constants
   * @return a string containing all the characters from the URL
   * @throws IOException if an I/O error occurs.
   */
  public static String toString(URL url, Charset charset) throws IOException {
    return asCharSource(url, charset).read();
  }

  /**
   * Streams lines from a URL, stopping when our callback returns false, or we have read all of the
   * lines.
   *
   * @param url the URL to read from
   * @param charset the charset used to decode the input stream; see {@link Charsets} for helpful
   *     predefined constants
   * @param callback the LineProcessor to use to handle the lines
   * @return the output of processing the lines
   * @throws IOException if an I/O error occurs
   */
  @CanIgnoreReturnValue // some processors won't return a useful result
  @ParametricNullness
  public static  T readLines(
      URL url, Charset charset, LineProcessor callback) throws IOException {
    return asCharSource(url, charset).readLines(callback);
  }

  /**
   * Reads all of the lines from a URL. The lines do not include line-termination characters, but do
   * include other leading and trailing whitespace.
   *
   * 

This method returns a mutable {@code List}. For an {@code ImmutableList}, use {@code * Resources.asCharSource(url, charset).readLines()}. * * @param url the URL to read from * @param charset the charset used to decode the input stream; see {@link Charsets} for helpful * predefined constants * @return a mutable {@link List} containing all the lines * @throws IOException if an I/O error occurs */ public static List readLines(URL url, Charset charset) throws IOException { // don't use asCharSource(url, charset).readLines() because that returns // an immutable list, which would change the behavior of this method return readLines( url, charset, new LineProcessor>() { final List result = Lists.newArrayList(); @Override public boolean processLine(String line) { result.add(line); return true; } @Override public List getResult() { return result; } }); } /** * Copies all bytes from a URL to an output stream. * * @param from the URL to read from * @param to the output stream * @throws IOException if an I/O error occurs */ public static void copy(URL from, OutputStream to) throws IOException { asByteSource(from).copyTo(to); } /** * Returns a {@code URL} pointing to {@code resourceName} if the resource is found using the * {@linkplain Thread#getContextClassLoader() context class loader}. In simple environments, the * context class loader will find resources from the class path. In environments where different * threads can have different class loaders, for example app servers, the context class loader * will typically have been set to an appropriate loader for the current thread. * *

In the unusual case where the context class loader is null, the class loader that loaded * this class ({@code Resources}) will be used instead. * * @throws IllegalArgumentException if the resource is not found */ @CanIgnoreReturnValue // being used to check if a resource exists // TODO(cgdecker): maybe add a better way to check if a resource exists // e.g. Optional tryGetResource or boolean resourceExists public static URL getResource(String resourceName) { ClassLoader loader = MoreObjects.firstNonNull( Thread.currentThread().getContextClassLoader(), Resources.class.getClassLoader()); URL url = loader.getResource(resourceName); checkArgument(url != null, "resource %s not found.", resourceName); return url; } /** * Given a {@code resourceName} that is relative to {@code contextClass}, returns a {@code URL} * pointing to the named resource. * * @throws IllegalArgumentException if the resource is not found */ @CanIgnoreReturnValue // being used to check if a resource exists public static URL getResource(Class contextClass, String resourceName) { URL url = contextClass.getResource(resourceName); checkArgument( url != null, "resource %s relative to %s not found.", resourceName, contextClass.getName()); return url; } }





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