Closeables.java revision 1d580d0f6ee4f21eb309ba7b509d2c6d671c4044 
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.util.logging.Level;
25import java.util.logging.Logger;
26
27import javax.annotation.Nullable;
28
29/**
30 * Utility methods for working with {@link Closeable} objects.
31 *
32 * @author Michael Lancaster
33 * @since 1.0
34 */
35@Beta
36public final class Closeables {
37  @VisibleForTesting static final Logger logger
38      = Logger.getLogger(Closeables.class.getName());
39
40  private Closeables() {}
41
42  /**
43   * Closes a {@link Closeable}, with control over whether an
44   * {@code IOException} may be thrown. This is primarily useful in a
45   * finally block, where a thrown exception needs to be logged but not
46   * propagated (otherwise the original exception will be lost).
47   *
48   * <p>If {@code swallowIOException} is true then we never throw
49   * {@code IOException} but merely log it.
50   *
51   * <p>Example:
52   *
53   * <p><pre>public void useStreamNicely() throws IOException {
54   * SomeStream stream = new SomeStream("foo");
55   * boolean threw = true;
56   * try {
57   *   // Some code which does something with the Stream. May throw a
58   *   // Throwable.
59   *   threw = false; // No throwable thrown.
60   * } finally {
61   *   // Close the stream.
62   *   // If an exception occurs, only rethrow it if (threw==false).
63   *   Closeables.close(stream, threw);
64   * }
65   * </pre>
66   *
67   * @param closeable the {@code Closeable} object to be closed, or null,
68   *     in which case this method does nothing
69   * @param swallowIOException if true, don't propagate IO exceptions
70   *     thrown by the {@code close} methods
71   * @throws IOException if {@code swallowIOException} is false and
72   *     {@code close} throws an {@code IOException}.
73   */
74  public static void close(@Nullable Closeable closeable,
75      boolean swallowIOException) throws IOException {
76    if (closeable == null) {
77      return;
78    }
79    try {
80      closeable.close();
81    } catch (IOException e) {
82      if (swallowIOException) {
83        logger.log(Level.WARNING,
84            "IOException thrown while closing Closeable.", e);
85      } else {
86        throw e;
87      }
88    }
89  }
90
91  /**
92   * Equivalent to calling {@code close(closeable, true)}, but with no
93   * IOException in the signature.
94   * @param closeable the {@code Closeable} object to be closed, or null, in
95   *      which case this method does nothing
96   */
97  public static void closeQuietly(@Nullable Closeable closeable) {
98    try {
99      close(closeable, true);
100    } catch (IOException e) {
101      logger.log(Level.SEVERE, "IOException should not have been thrown.", e);
102    }
103  }
104}
105