    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 * </p>
    052 * <pre>
    053 * TaggedWriter writer = new TaggedWriter(...);
    054 * try {
    055 *     writeToWriter(writer);
    056 * } catch (IOException e) {
    057 *     writer.throwIfCauseOf(e);
    058 *     // ... or process the exception that was caused by something else
    059 * }
    060 * </pre>
    061 *
    062 * @see TaggedIOException
    063 * @since 2.0
    064 */
    065public class TaggedWriter extends ProxyWriter {
    066
    067    /**
    068     * The unique tag associated with exceptions from writer.
    069     */
    070    private final Serializable tag = UUID.randomUUID();
    071
    072    /**
    073     * Constructs a tagging decorator for the given writer.
    074     *
    075     * @param proxy writer to be decorated
    076     */
    077    public TaggedWriter(final Writer proxy) {
    078        super(proxy);
    079    }
    080
    081    /**
    082     * Tags any IOExceptions thrown, wrapping and re-throwing.
    083     *
    084     * @param e The IOException thrown
    085     * @throws IOException if an I/O error occurs.
    086     */
    087    @Override
    088    protected void handleIOException(final IOException e) throws IOException {
    089        throw new TaggedIOException(e, tag);
    090    }
    091
    092    /**
    093     * Tests if the given exception was caused by this writer.
    094     *
    095     * @param exception an exception
    096     * @return {@code true} if the exception was thrown by this writer,
    097     *         {@code false} otherwise
    098     */
    099    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}