java.com.google.common.io.Resources Maven / Gradle / Ivy
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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.Beta;
import com.google.common.annotations.GwtIncompatible;
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;
/**
* 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.
*
* All method parameters must be non-null unless documented otherwise.
*
* @author Chris Nokleberg
* @author Ben Yu
* @author Colin Decker
* @since 1.0
*/
@Beta
@GwtIncompatible
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
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
*/
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;
}
}