1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.io.output;
18
19 import java.io.IOException;
20 import java.io.OutputStream;
21 import java.io.Serializable;
22 import java.util.UUID;
23
24 import org.apache.commons.io.TaggedIOException;
25
26 /**
27 * An output stream decorator that tags potential exceptions so that the
28 * stream that caused the exception can easily be identified. This is
29 * done by using the {@link TaggedIOException} class to wrap all thrown
30 * {@link IOException}s. See below for an example of using this class.
31 * <pre>
32 * TaggedOutputStream stream = new TaggedOutputStream(...);
33 * try {
34 * // Processing that may throw an IOException either from this stream
35 * // or from some other IO activity like temporary files, etc.
36 * writeToStream(stream);
37 * } catch (IOException e) {
38 * if (stream.isCauseOf(e)) {
39 * // The exception was caused by this stream.
40 * // Use e.getCause() to get the original exception.
41 * } else {
42 * // The exception was caused by something else.
43 * }
44 * }
45 * </pre>
46 * <p>
47 * Alternatively, the {@link #throwIfCauseOf(Exception)} method can be
48 * used to let higher levels of code handle the exception caused by this
49 * stream while other processing errors are being taken care of at this
50 * lower level.
51 * <pre>
52 * TaggedOutputStream stream = new TaggedOutputStream(...);
53 * try {
54 * writeToStream(stream);
55 * } catch (IOException e) {
56 * stream.throwIfCauseOf(e);
57 * // ... or process the exception that was caused by something else
58 * }
59 * </pre>
60 *
61 * @see TaggedIOException
62 * @since 2.0
63 */
64 public class TaggedOutputStream extends ProxyOutputStream {
65
66 /**
67 * The unique tag associated with exceptions from stream.
68 */
69 private final Serializable tag = UUID.randomUUID();
70
71 /**
72 * Creates a tagging decorator for the given output stream.
73 *
74 * @param proxy output stream to be decorated
75 */
76 public TaggedOutputStream(final OutputStream proxy) {
77 super(proxy);
78 }
79
80 /**
81 * Tests if the given exception was caused by this stream.
82 *
83 * @param exception an exception
84 * @return {@code true} if the exception was thrown by this stream,
85 * {@code false} otherwise
86 */
87 public boolean isCauseOf(final Exception exception) {
88 return TaggedIOException.isTaggedWith(exception, tag);
89 }
90
91 /**
92 * Re-throws the original exception thrown by this stream. This method
93 * first checks whether the given exception is a {@link TaggedIOException}
94 * wrapper created by this decorator, and then unwraps and throws the
95 * original wrapped exception. Returns normally if the exception was
96 * not thrown by this stream.
97 *
98 * @param exception an exception
99 * @throws IOException original exception, if any, thrown by this stream
100 */
101 public void throwIfCauseOf(final Exception exception) throws IOException {
102 TaggedIOException.throwCauseIfTaggedWith(exception, tag);
103 }
104
105 /**
106 * Tags any IOExceptions thrown, wrapping and re-throwing.
107 *
108 * @param e The IOException thrown
109 * @throws IOException if an I/O error occurs
110 */
111 @Override
112 protected void handleIOException(final IOException e) throws IOException {
113 throw new TaggedIOException(e, tag);
114 }
115
116 }