src/main/java/org/apache/commons/io/IOExceptionList.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.commons.io;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Objects;

/**
 * An IOException based on a list of Throwable causes.
 * <p>
 * The first exception in the list is used as this exception's cause and is accessible with the usual
 * {@link #getCause()} while the complete list is accessible with {@link #getCauseList()}.
 * </p>
 *
 * @since 2.7
 */
public class IOExceptionList extends IOException implements Iterable<Throwable> {

    private static final long serialVersionUID = 1L;

    /**
     * Throws this exception if the list is not null or empty.
     *
     * @param causeList The list to test.
     * @param message The detail message, see {@link #getMessage()}.
     * @throws IOExceptionList if the list is not null or empty.
     * @since 2.12.0
     */
    public static void checkEmpty(final List<? extends Throwable> causeList, final Object message) throws IOExceptionList {
        if (!isEmpty(causeList)) {
            throw new IOExceptionList(Objects.toString(message, null), causeList);
        }
    }

    private static boolean isEmpty(final List<? extends Throwable> causeList) {
        return size(causeList) == 0;
    }

    private static int size(final List<? extends Throwable> causeList) {
        return causeList != null ? causeList.size() : 0;
    }

    private static String toMessage(final List<? extends Throwable> causeList) {
        return String.format("%,d exception(s): %s", size(causeList), causeList);
    }

    /**
     * List of causes.
     */
    private final List<? extends Throwable> causeList;

    /**
     * Constructs a new exception caused by a list of exceptions.
     *
     * @param causeList a list of cause exceptions.
     */
    public IOExceptionList(final List<? extends Throwable> causeList) {
        this(toMessage(causeList), causeList);
    }

    /**
     * Constructs a new exception caused by a list of exceptions.
     *
     * @param message The detail message, see {@link #getMessage()}.
     * @param causeList a list of cause exceptions.
     * @since 2.9.0
     */
    public IOExceptionList(final String message, final List<? extends Throwable> causeList) {
        super(message != null ? message : toMessage(causeList), isEmpty(causeList) ? null : causeList.get(0));
        this.causeList = causeList == null ? Collections.emptyList() : causeList;
    }

    /**
     * Gets the cause exception at the given index.
     *
     * @param <T> type of exception to return.
     * @param index index in the cause list.
     * @return The list of causes.
     */
    public <T extends Throwable> T getCause(final int index) {
        return (T) causeList.get(index);
    }

    /**
     * Gets the cause exception at the given index.
     *
     * @param <T> type of exception to return.
     * @param index index in the cause list.
     * @param clazz type of exception to return.
     * @return The list of causes.
     */
    public <T extends Throwable> T getCause(final int index, final Class<T> clazz) {
        return clazz.cast(getCause(index));
    }

    /**
     * Gets the cause list.
     *
     * @param <T> type of exception to return.
     * @return The list of causes.
     */
    public <T extends Throwable> List<T> getCauseList() {
        return (List<T>) new ArrayList<>(causeList);
    }

    /**
     * Works around Throwable and Generics, may fail at runtime depending on the argument value.
     *
     * @param <T> type of exception to return.
     * @param clazz the target type
     * @return The list of causes.
     */
    public <T extends Throwable> List<T> getCauseList(final Class<T> clazz) {
        return (List<T>) new ArrayList<>(causeList);
    }

    @Override
    public Iterator<Throwable> iterator() {
        return getCauseList().iterator();
    }

}