    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;
    018
    019import java.io.IOException;
    020import java.io.Serializable;
    021
    022/**
    023 * An {@link IOException} decorator that adds a serializable tag to the
    024 * wrapped exception. Both the tag and the original exception can be used
    025 * to determine further processing when this exception is caught.
    026 *
    027 * @since 2.0
    028 */
    029@SuppressWarnings("deprecation") // needs to extend deprecated IOExceptionWithCause to preserve binary compatibility
    030public class TaggedIOException extends IOExceptionWithCause {
    031
    032    /**
    033     * Generated serial version UID.
    034     */
    035    private static final long serialVersionUID = -6994123481142850163L;
    036
    037    /**
    038     * Checks whether the given throwable is tagged with the given tag.
    039     * <p>
    040     * This check can only succeed if the throwable is a
    041     * {@link TaggedIOException} and the tag is {@link Serializable}, but
    042     * the argument types are intentionally more generic to make it easier
    043     * to use this method without type casts.
    044     * <p>
    045     * A typical use for this method is in a {@code catch} block to
    046     * determine how a caught exception should be handled:
    047     * <pre>
    048     * Serializable tag = ...;
    049     * try {
    050     *     ...;
    051     * } catch (Throwable t) {
    052     *     if (TaggedIOException.isTaggedWith(t, tag)) {
    053     *         // special processing for tagged exception
    054     *     } else {
    055     *         // handling of other kinds of exceptions
    056     *     }
    057     * }
    058     * </pre>
    059     *
    060     * @param throwable The Throwable object to check
    061     * @param tag tag object
    062     * @return {@code true} if the throwable has the specified tag,
    063     * otherwise {@code false}
    064     */
    065    public static boolean isTaggedWith(final Throwable throwable, final Object tag) {
    066        return tag != null
    067            && throwable instanceof TaggedIOException
    068            && tag.equals(((TaggedIOException) throwable).tag);
    069    }
    070
    071    /**
    072     * Throws the original {@link IOException} if the given throwable is
    073     * a {@link TaggedIOException} decorator the given tag. Does nothing
    074     * if the given throwable is of a different type or if it is tagged
    075     * with some other tag.
    076     * <p>
    077     * This method is typically used in a {@code catch} block to
    078     * selectively rethrow tagged exceptions.
    079     * <pre>
    080     * Serializable tag = ...;
    081     * try {
    082     *     ...;
    083     * } catch (Throwable t) {
    084     *     TaggedIOException.throwCauseIfTagged(t, tag);
    085     *     // handle other kinds of exceptions
    086     * }
    087     * </pre>
    088     *
    089     * @param throwable an exception
    090     * @param tag tag object
    091     * @throws IOException original exception from the tagged decorator, if any
    092     */
    093    public static void throwCauseIfTaggedWith(final Throwable throwable, final Object tag)
    094            throws IOException {
    095        if (isTaggedWith(throwable, tag)) {
    096            throw ((TaggedIOException) throwable).getCause();
    097        }
    098    }
    099
    100    /**
    101     * The tag of this exception.
    102     */
    103    private final Serializable tag;
    104
    105    /**
    106     * Creates a tagged wrapper for the given exception.
    107     *
    108     * @param original the exception to be tagged
    109     * @param tag tag of this exception
    110     */
    111    public TaggedIOException(final IOException original, final Serializable tag) {
    112        super(original.getMessage(), original);
    113        this.tag = tag;
    114    }
    115
    116    /**
    117     * Returns the serializable tag object.
    118     *
    119     * @return tag object
    120     */
    121    public Serializable getTag() {
    122        return tag;
    123    }
    124
    125    /**
    126     * Returns the wrapped exception. The only difference to the overridden
    127     * {@link Throwable#getCause()} method is the narrower return type.
    128     *
    129     * @return wrapped exception
    130     */
    131    @Override
    132    public synchronized IOException getCause() {
    133        return (IOException) super.getCause();
    134    }
    135
    136}