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1   /*
2    * Copyright 2006-2007 the original author or authors.
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  package org.springframework.batch.support;
17  
18  import java.io.IOException;
19  import java.util.Comparator;
20  
21  import org.springframework.core.io.Resource;
22  import org.springframework.util.Assert;
23  
24  /**
25   * Comparator to sort resources by the file last modified time.
26   * 
27   * @author Dave Syer
28   * 
29   */
30  public class LastModifiedResourceComparator implements Comparator<Resource> {
31  
32  	/**
33  	 * Compare the two resources by last modified time, so that a sorted list of
34  	 * resources will have oldest first.
35  	 * 
36  	 * @throws IllegalArgumentException if one of the resources doesn't exist or
37  	 * its last modified date cannot be determined
38  	 * 
39  	 * @see Comparator#compare(Object, Object)
40  	 */
41      @Override
42  	public int compare(Resource r1, Resource r2) {
43  		Assert.isTrue(r1.exists(), "Resource does not exist: " + r1);
44  		Assert.isTrue(r2.exists(), "Resource does not exist: " + r2);
45  		try {
46  			long diff = r1.getFile().lastModified() - r2.getFile().lastModified();
47  			return diff > 0 ? 1 : diff < 0 ? -1 : 0;
48  		}
49  		catch (IOException e) {
50  			throw new IllegalArgumentException("Resource modification times cannot be determined (unexpected).", e);
51  		}
52  	}
53  
54  }