Closeables.java revision 3ecfa412eddc4b084663f38d562537b86b9734d5 
1/*
2 * Copyright (C) 2007 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.io;
18
19import com.google.common.annotations.Beta;
20import com.google.common.annotations.VisibleForTesting;
21
22import java.io.Closeable;
23import java.io.IOException;
24import java.io.InputStream;
25import java.io.Reader;
26import java.util.logging.Level;
27import java.util.logging.Logger;
28
29import javax.annotation.Nullable;
30
31/**
32 * Utility methods for working with {@link Closeable} objects.
33 *
34 * @author Michael Lancaster
35 * @since 1.0
36 */
37@Beta
38public final class Closeables {
39  @VisibleForTesting static final Logger logger
40      = Logger.getLogger(Closeables.class.getName());
41
42  private Closeables() {}
43
44  /**
45   * Closes a {@link Closeable}, with control over whether an {@code IOException} may be thrown.
46   * This is primarily useful in a finally block, where a thrown exception needs to be logged but
47   * not propagated (otherwise the original exception will be lost).
48   *
49   * <p>If {@code swallowIOException} is true then we never throw {@code IOException} but merely log
50   * it.
51   *
52   * <p>Example: <pre>   {@code
53   *
54   *   public void useStreamNicely() throws IOException {
55   *     SomeStream stream = new SomeStream("foo");
56   *     boolean threw = true;
57   *     try {
58   *       // ... code which does something with the stream ...
59   *       threw = false;
60   *     } finally {
61   *       // If an exception occurs, rethrow it only if threw==false:
62   *       Closeables.close(stream, threw);
63   *     }
64   *   }}</pre>
65   *
66   * @param closeable the {@code Closeable} object to be closed, or null, in which case this method
67   *     does nothing
68   * @param swallowIOException if true, don't propagate IO exceptions thrown by the {@code close}
69   *     methods
70   * @throws IOException if {@code swallowIOException} is false and {@code close} throws an
71   *     {@code IOException}.
72   */
73  public static void close(@Nullable Closeable closeable,
74      boolean swallowIOException) throws IOException {
75    if (closeable == null) {
76      return;
77    }
78    try {
79      closeable.close();
80    } catch (IOException e) {
81      if (swallowIOException) {
82        logger.log(Level.WARNING,
83            "IOException thrown while closing Closeable.", e);
84      } else {
85        throw e;
86      }
87    }
88  }
89
90  /**
91   * Closes the given {@link InputStream}, logging any {@code IOException} that's thrown rather
92   * than propagating it.
93   *
94   * <p>While it's not safe in the general case to ignore exceptions that are thrown when closing
95   * an I/O resource, it should generally be safe in the case of a resource that's being used only
96   * for reading, such as an {@code InputStream}. Unlike with writable resources, there's no
97   * chance that a failure that occurs when closing the stream indicates a meaningful problem such
98   * as a failure to flush all bytes to the underlying resource.
99   *
100   * @param inputStream the input stream to be closed, or {@code null} in which case this method
101   *     does nothing
102   * @since 17.0
103   */
104  public static void closeQuietly(@Nullable InputStream inputStream) {
105    try {
106      close(inputStream, true);
107    } catch (IOException impossible) {
108      throw new AssertionError(impossible);
109    }
110  }
111
112  /**
113   * Closes the given {@link Reader}, logging any {@code IOException} that's thrown rather than
114   * propagating it.
115   *
116   * <p>While it's not safe in the general case to ignore exceptions that are thrown when closing
117   * an I/O resource, it should generally be safe in the case of a resource that's being used only
118   * for reading, such as a {@code Reader}. Unlike with writable resources, there's no chance that
119   * a failure that occurs when closing the reader indicates a meaningful problem such as a failure
120   * to flush all bytes to the underlying resource.
121   *
122   * @param reader the reader to be closed, or {@code null} in which case this method does nothing
123   * @since 17.0
124   */
125  public static void closeQuietly(@Nullable Reader reader) {
126    try {
127      close(reader, true);
128    } catch (IOException impossible) {
129      throw new AssertionError(impossible);
130    }
131  }
132}
133