EaglerForge/sources/main/java/com/google/common/io/Closeables.java

/*
 * 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 java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.util.logging.Level;
import java.util.logging.Logger;

import javax.annotation.Nullable;

import com.google.common.annotations.Beta;
import com.google.common.annotations.VisibleForTesting;

/**
 * Utility methods for working with {@link Closeable} objects.
 *
 * @author Michael Lancaster
 * @since 1.0
 */
@Beta
public final class Closeables {
	@VisibleForTesting
	static final Logger logger = Logger.getLogger(Closeables.class.getName());

	private Closeables() {
	}

	/**
	 * Closes a {@link Closeable}, with control over whether an {@code IOException}
	 * may be thrown. This is primarily useful in a finally block, where a thrown
	 * exception needs to be logged but not propagated (otherwise the original
	 * exception will be lost).
	 *
	 * <p>
	 * If {@code swallowIOException} is true then we never throw {@code IOException}
	 * but merely log it.
	 *
	 * <p>
	 * Example:
	 * 
	 * <pre>
	 *    {@code
	 *
	 *   public void useStreamNicely() throws IOException {
	 *     SomeStream stream = new SomeStream("foo");
	 *     boolean threw = true;
	 *     try {
	 *       // ... code which does something with the stream ...
	 *       threw = false;
	 *     } finally {
	 *       // If an exception occurs, rethrow it only if threw==false:
	 *       Closeables.close(stream, threw);
	 *     }
	 *   }}
	 * </pre>
	 *
	 * @param closeable          the {@code Closeable} object to be closed, or null,
	 *                           in which case this method does nothing
	 * @param swallowIOException if true, don't propagate IO exceptions thrown by
	 *                           the {@code close} methods
	 * @throws IOException if {@code swallowIOException} is false and {@code close}
	 *                     throws an {@code IOException}.
	 */
	public static void close(@Nullable Closeable closeable, boolean swallowIOException) throws IOException {
		if (closeable == null) {
			return;
		}
		try {
			closeable.close();
		} catch (IOException e) {
			if (swallowIOException) {
				logger.log(Level.WARNING, "IOException thrown while closing Closeable.", e);
			} else {
				throw e;
			}
		}
	}

	/**
	 * Closes the given {@link InputStream}, logging any {@code IOException} that's
	 * thrown rather than propagating it.
	 *
	 * <p>
	 * While it's not safe in the general case to ignore exceptions that are thrown
	 * when closing an I/O resource, it should generally be safe in the case of a
	 * resource that's being used only for reading, such as an {@code InputStream}.
	 * Unlike with writable resources, there's no chance that a failure that occurs
	 * when closing the stream indicates a meaningful problem such as a failure to
	 * flush all bytes to the underlying resource.
	 *
	 * @param inputStream the input stream to be closed, or {@code null} in which
	 *                    case this method does nothing
	 * @since 17.0
	 */
	public static void closeQuietly(@Nullable InputStream inputStream) {
		try {
			close(inputStream, true);
		} catch (IOException impossible) {
			throw new AssertionError(impossible);
		}
	}

	/**
	 * Closes the given {@link Reader}, logging any {@code IOException} that's
	 * thrown rather than propagating it.
	 *
	 * <p>
	 * While it's not safe in the general case to ignore exceptions that are thrown
	 * when closing an I/O resource, it should generally be safe in the case of a
	 * resource that's being used only for reading, such as a {@code Reader}. Unlike
	 * with writable resources, there's no chance that a failure that occurs when
	 * closing the reader indicates a meaningful problem such as a failure to flush
	 * all bytes to the underlying resource.
	 *
	 * @param reader the reader to be closed, or {@code null} in which case this
	 *               method does nothing
	 * @since 17.0
	 */
	public static void closeQuietly(@Nullable Reader reader) {
		try {
			close(reader, true);
		} catch (IOException impossible) {
			throw new AssertionError(impossible);
		}
	}
}