001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.io.output;
018
019import java.io.IOException;
020import java.io.Serializable;
021import java.io.Writer;
022import java.util.UUID;
023
024import org.apache.commons.io.TaggedIOException;
025
026/**
027 * A writer decorator that tags potential exceptions so that the
028 * reader that caused the exception can easily be identified. This is
029 * done by using the {@link TaggedIOException} class to wrap all thrown
030 * {@link IOException}s. See below for an example of using this class.
031 * <pre>
032 * TaggedReader reader = new TaggedReader(...);
033 * try {
034 *     // Processing that may throw an IOException either from this reader
035 *     // or from some other IO activity like temporary files, etc.
036 *     writeToWriter(writer);
037 * } catch (IOException e) {
038 *     if (writer.isCauseOf(e)) {
039 *         // The exception was caused by this writer.
040 *         // Use e.getCause() to get the original exception.
041 *     } else {
042 *         // The exception was caused by something else.
043 *     }
044 * }
045 * </pre>
046 * <p>
047 * Alternatively, the {@link #throwIfCauseOf(Exception)} method can be
048 * used to let higher levels of code handle the exception caused by this
049 * writer while other processing errors are being taken care of at this
050 * lower level.
051 * <pre>
052 * TaggedWriter writer = new TaggedWriter(...);
053 * try {
054 *     writeToWriter(writer);
055 * } catch (IOException e) {
056 *     writer.throwIfCauseOf(e);
057 *     // ... or process the exception that was caused by something else
058 * }
059 * </pre>
060 *
061 * @see TaggedIOException
062 * @since 2.0
063 */
064public class TaggedWriter extends ProxyWriter {
065
066    /**
067     * The unique tag associated with exceptions from writer.
068     */
069    private final Serializable tag = UUID.randomUUID();
070
071    /**
072     * Creates a tagging decorator for the given writer.
073     *
074     * @param proxy writer to be decorated
075     */
076    public TaggedWriter(final Writer proxy) {
077        super(proxy);
078    }
079
080    /**
081     * Tests if the given exception was caused by this writer.
082     *
083     * @param exception an exception
084     * @return {@code true} if the exception was thrown by this writer,
085     *         {@code false} otherwise
086     */
087    public boolean isCauseOf(final Exception exception) {
088        return TaggedIOException.isTaggedWith(exception, tag);
089    }
090
091    /**
092     * Re-throws the original exception thrown by this writer. This method
093     * first checks whether the given exception is a {@link TaggedIOException}
094     * wrapper created by this decorator, and then unwraps and throws the
095     * original wrapped exception. Returns normally if the exception was
096     * not thrown by this writer.
097     *
098     * @param exception an exception
099     * @throws IOException original exception, if any, thrown by this writer
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}