IN PROGRESS - BATCH-520: Add a Delegating File Reader For Multiple Files

added SortedMultiResourceItemReader which sorts the injected Resources using Comparator

spring-batch-infrastructure/src/test/java/org/springframework/batch/item/SortedMultiResourceItemReaderTests.java

@@ -0,0 +1,62 @@
+package org.springframework.batch.item;
+
+import java.util.Comparator;
+
+import junit.framework.TestCase;
+
+import org.springframework.core.io.FileSystemResource;
+import org.springframework.core.io.Resource;
+
+/**
+ * Tests for {@link SortedMultiResourceItemReader}.
+ */
+public class SortedMultiResourceItemReaderTests extends TestCase {
+
+	private SortedMultiResourceItemReader tested = new SortedMultiResourceItemReader();
+
+	private Resource r1 = new FileSystemResource("b");
+
+	private Resource r2 = new FileSystemResource("a");
+
+	private Resource r3 = new FileSystemResource("c");
+
+	private Resource[] resources = { r1, r2, r3 };
+
+	/**
+	 * Resources are ordered according to filename by default.
+	 */
+	public void testResourceOrdering() {
+
+		tested.setResources(resources);
+
+		assertSame(r2, resources[0]);
+		assertSame(r1, resources[1]);
+		assertSame(r3, resources[2]);
+
+	}
+
+	/**
+	 * Resources are ordered according to injected comparator.
+	 */
+	public void testResourceOrderingWithCustomComparator() {
+		Comparator comp = new Comparator() {
+
+			/**
+			 * Reversed ordering by filename.
+			 */
+			public int compare(Object o1, Object o2) {
+				Resource r1 = (Resource) o1;
+				Resource r2 = (Resource) o2;
+				return -r1.getFilename().compareTo(r2.getFilename());
+			}
+
+		};
+
+		tested.setComparator(comp);
+		tested.setResources(resources);
+
+		assertSame(r3, resources[0]);
+		assertSame(r1, resources[1]);
+		assertSame(r2, resources[2]);
+	}
+}