Java tutorial
/* * 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. * * <p>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> T readLines(URL url, Charset charset, LineProcessor<T> 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. * * <p>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<String> 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<List<String>>() { final List<String> result = Lists.newArrayList(); @Override public boolean processLine(String line) { result.add(line); return true; } @Override public List<String> 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. * * <p>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; } }