    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}