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.Reader;
021import java.io.Serializable;
022import java.util.UUID;
023
024import org.apache.commons.io.TaggedIOException;
025
026/**
027 * A reader decorator that tags potential exceptions so that the reader that caused the exception can easily be
028 * identified. This is done by using the {@link TaggedIOException} class to wrap all thrown {@link IOException}s. See
029 * below for an example of using this class.
030 *
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 *     processReader(reader);
037 * } catch (IOException e) {
038 *     if (reader.isCauseOf(e)) {
039 *         // The exception was caused by this reader.
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 used to let higher levels of code handle the
048 * exception caused by this reader while other processing errors are being taken care of at this lower level.
049 * </p>
050 *
051 * <pre>
052 * TaggedReader reader = new TaggedReader(...);
053 * try {
054 *     processReader(reader);
055 * } catch (IOException e) {
056 *     reader.throwIfCauseOf(e);
057 *     // ... or process the exception that was caused by something else
058 * }
059 * </pre>
060 *
061 * @see TaggedIOException
062 * @since 2.7
063 */
064public class TaggedReader extends ProxyReader {
065
066    /**
067     * The unique tag associated with exceptions from reader.
068     */
069    private final Serializable tag = UUID.randomUUID();
070
071    /**
072     * Creates a tagging decorator for the given reader.
073     *
074     * @param proxy reader to be decorated
075     */
076    public TaggedReader(final Reader proxy) {
077        super(proxy);
078    }
079
080    /**
081     * Tests if the given exception was caused by this reader.
082     *
083     * @param exception an exception
084     * @return {@code true} if the exception was thrown by this reader, {@code false} otherwise
085     */
086    public boolean isCauseOf(final Throwable exception) {
087        return TaggedIOException.isTaggedWith(exception, tag);
088    }
089
090    /**
091     * Re-throws the original exception thrown by this reader. This method first checks whether the given exception is a
092     * {@link TaggedIOException} wrapper created by this decorator, and then unwraps and throws the original wrapped
093     * exception. Returns normally if the exception was not thrown by this reader.
094     *
095     * @param throwable an exception
096     * @throws IOException original exception, if any, thrown by this reader
097     */
098    public void throwIfCauseOf(final Throwable throwable) throws IOException {
099        TaggedIOException.throwCauseIfTaggedWith(throwable, tag);
100    }
101
102    /**
103     * Tags any IOExceptions thrown, wrapping and re-throwing.
104     *
105     * @param e The IOException thrown
106     * @throws IOException if an I/O error occurs.
107     */
108    @Override
109    protected void handleIOException(final IOException e) throws IOException {
110        throw new TaggedIOException(e, tag);
111    }
112
113}