    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.OutputStream;
    021import java.io.Serializable;
    022import java.util.UUID;
    023
    024import org.apache.commons.io.TaggedIOException;
    025
    026/**
    027 * An output stream decorator that tags potential exceptions so that the
    028 * stream 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 * TaggedOutputStream stream = new TaggedOutputStream(...);
    033 * try {
    034 *     // Processing that may throw an IOException either from this stream
    035 *     // or from some other IO activity like temporary files, etc.
    036 *     writeToStream(stream);
    037 * } catch (IOException e) {
    038 *     if (stream.isCauseOf(e)) {
    039 *         // The exception was caused by this stream.
    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 * stream while other processing errors are being taken care of at this
    050 * lower level.
    051 * <pre>
    052 * TaggedOutputStream stream = new TaggedOutputStream(...);
    053 * try {
    054 *     writeToStream(stream);
    055 * } catch (IOException e) {
    056 *     stream.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 TaggedOutputStream extends ProxyOutputStream {
    065
    066    /**
    067     * The unique tag associated with exceptions from stream.
    068     */
    069    private final Serializable tag = UUID.randomUUID();
    070
    071    /**
    072     * Creates a tagging decorator for the given output stream.
    073     *
    074     * @param proxy output stream to be decorated
    075     */
    076    public TaggedOutputStream(final OutputStream proxy) {
    077        super(proxy);
    078    }
    079
    080    /**
    081     * Tests if the given exception was caused by this stream.
    082     *
    083     * @param exception an exception
    084     * @return {@code true} if the exception was thrown by this stream,
    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 stream. 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 stream.
    097     *
    098     * @param exception an exception
    099     * @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}