Add comparator for sorting files by last modified date (useful for MultiResourceItemReader).

spring-batch-infrastructure/src/main/java/org/springframework/batch/support/LastModifiedResourceComparator.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2006-2007 the original author or authors.
+ *
+ * Licensed 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.springframework.batch.support;
+
+import java.io.IOException;
+import java.util.Comparator;
+
+import org.springframework.core.io.Resource;
+import org.springframework.util.Assert;
+
+/**
+ * Comparator to sort resources by the file last modified time.
+ * 
+ * @author Dave Syer
+ * 
+ */
+public class LastModifiedResourceComparator implements Comparator<Resource> {
+
+	/**
+	 * Compare the two resources by last modified time, so that a sorted list of
+	 * resources will have oldest first.
+	 * 
+	 * @throws IllegalArgumentException if one of the resources doesn't exist or
+	 * its last modified date cannot be determined
+	 * 
+	 * @see Comparator#compare(Object, Object)
+	 */
+	public int compare(Resource r1, Resource r2) {
+		Assert.isTrue(r1.exists(), "Resource does not exist: " + r1);
+		Assert.isTrue(r2.exists(), "Resource does not exist: " + r2);
+		try {
+			long diff = r1.getFile().lastModified() - r2.getFile().lastModified();
+			return diff > 0 ? 1 : diff < 0 ? -1 : 0;
+		}
+		catch (IOException e) {
+			throw new IllegalArgumentException("Resource modification times cannot be determined (unexpected).", e);
+		}
+	}
+
+}