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.Serializable;
21 import java.io.Writer;
22 import java.util.UUID;
23
24 import org.apache.commons.io.TaggedIOException;
25
26 /**
27 * A writer decorator that tags potential exceptions so that the
28 * reader 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 * TaggedReader reader = new TaggedReader(...);
33 * try {
34 * // Processing that may throw an IOException either from this reader
35 * // or from some other IO activity like temporary files, etc.
36 * writeToWriter(writer);
37 * } catch (IOException e) {
38 * if (writer.isCauseOf(e)) {
39 * // The exception was caused by this writer.
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 * writer while other processing errors are being taken care of at this
50 * lower level.
51 * </p>
52 * <pre>
53 * TaggedWriter writer = new TaggedWriter(...);
54 * try {
55 * writeToWriter(writer);
56 * } catch (IOException e) {
57 * writer.throwIfCauseOf(e);
58 * // ... or process the exception that was caused by something else
59 * }
60 * </pre>
61 *
62 * @see TaggedIOException
63 * @since 2.0
64 */
65 public class TaggedWriter extends ProxyWriter {
66
67 /**
68 * The unique tag associated with exceptions from writer.
69 */
70 private final Serializable tag = UUID.randomUUID();
71
72 /**
73 * Constructs a tagging decorator for the given writer.
74 *
75 * @param proxy writer to be decorated
76 */
77 public TaggedWriter(final Writer proxy) {
78 super(proxy);
79 }
80
81 /**
82 * Tags any IOExceptions thrown, wrapping and re-throwing.
83 *
84 * @param e The IOException thrown
85 * @throws IOException if an I/O error occurs.
86 */
87 @Override
88 protected void handleIOException(final IOException e) throws IOException {
89 throw new TaggedIOException(e, tag);
90 }
91
92 /**
93 * Tests if the given exception was caused by this writer.
94 *
95 * @param exception an exception
96 * @return {@code true} if the exception was thrown by this writer,
97 * {@code false} otherwise
98 */
99 public boolean isCauseOf(final Exception exception) {
100 return TaggedIOException.isTaggedWith(exception, tag);
101 }
102
103 /**
104 * Re-throws the original exception thrown by this writer. This method
105 * first checks whether the given exception is a {@link TaggedIOException}
106 * wrapper created by this decorator, and then unwraps and throws the
107 * original wrapped exception. Returns normally if the exception was
108 * not thrown by this writer.
109 *
110 * @param exception an exception
111 * @throws IOException original exception, if any, thrown by this writer
112 */
113 public void throwIfCauseOf(final Exception exception) throws IOException {
114 TaggedIOException.throwCauseIfTaggedWith(exception, tag);
115 }
116
117 }