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.base.Charsets;
import com.google.common.base.MoreObjects;
import com.google.common.collect.Lists;
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
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
*/
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
*/
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;
}
}