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.input;
018
019import java.io.IOException;
020import java.io.InputStream;
021import java.io.Serializable;
022import java.util.UUID;
023
024import org.apache.commons.io.TaggedIOException;
025
026/**
027 * An input 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 * TaggedInputStream stream = new TaggedInputStream(...);
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 *     processStream(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(Throwable)} 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 * </p>
052 * <pre>
053 * TaggedInputStream stream = new TaggedInputStream(...);
054 * try {
055 *     processStream(stream);
056 * } catch (IOException e) {
057 *     stream.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 TaggedInputStream extends ProxyInputStream {
066
067    /**
068     * The unique tag associated with exceptions from stream.
069     */
070    private final Serializable tag = UUID.randomUUID();
071
072    /**
073     * Creates a tagging decorator for the given input stream.
074     *
075     * @param proxy input stream to be decorated
076     */
077    public TaggedInputStream(final InputStream proxy) {
078        super(proxy);
079    }
080
081    /**
082     * Tests if the given exception was caused by this stream.
083     *
084     * @param exception an exception
085     * @return {@code true} if the exception was thrown by this stream,
086     *         {@code false} otherwise
087     */
088    public boolean isCauseOf(final Throwable exception) {
089        return TaggedIOException.isTaggedWith(exception, tag);
090    }
091
092    /**
093     * Re-throws the original exception thrown by this stream. This method
094     * first checks whether the given exception is a {@link TaggedIOException}
095     * wrapper created by this decorator, and then unwraps and throws the
096     * original wrapped exception. Returns normally if the exception was
097     * not thrown by this stream.
098     *
099     * @param throwable an exception
100     * @throws IOException original exception, if any, thrown by this stream
101     */
102    public void throwIfCauseOf(final Throwable throwable) throws IOException {
103        TaggedIOException.throwCauseIfTaggedWith(throwable, tag);
104    }
105
106    /**
107     * Tags any IOExceptions thrown, wrapping and re-throwing.
108     *
109     * @param e The IOException thrown
110     * @throws IOException if an I/O error occurs.
111     */
112    @Override
113    protected void handleIOException(final IOException e) throws IOException {
114        throw new TaggedIOException(e, tag);
115    }
116
117}