001/*
002 * Copyright 2006-2007 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016package org.springframework.batch.support;
017
018import java.io.IOException;
019import java.util.Comparator;
020
021import org.springframework.core.io.Resource;
022import org.springframework.util.Assert;
023
024/**
025 * Comparator to sort resources by the file last modified time.
026 * 
027 * @author Dave Syer
028 * 
029 */
030public class LastModifiedResourceComparator implements Comparator<Resource> {
031
032        /**
033         * Compare the two resources by last modified time, so that a sorted list of
034         * resources will have oldest first.
035         * 
036         * @throws IllegalArgumentException if one of the resources doesn't exist or
037         * its last modified date cannot be determined
038         * 
039         * @see Comparator#compare(Object, Object)
040         */
041    @Override
042        public int compare(Resource r1, Resource r2) {
043                Assert.isTrue(r1.exists(), "Resource does not exist: " + r1);
044                Assert.isTrue(r2.exists(), "Resource does not exist: " + r2);
045                try {
046                        long diff = r1.getFile().lastModified() - r2.getFile().lastModified();
047                        return diff > 0 ? 1 : diff < 0 ? -1 : 0;
048                }
049                catch (IOException e) {
050                        throw new IllegalArgumentException("Resource modification times cannot be determined (unexpected).", e);
051                }
052        }
053
054}