Make a SimpleJobIdentifierFactory for SimpleJobIdentifiers

OPEN - issue BATCH-58: Make JobStream and JobRun optional properties of Job (e.g. through join to optional table) 
http://opensource.atlassian.com/projects/spring/browse/BATCH-58

execution/src/main/java/org/springframework/batch/execution/repository/dao/JobInstanceFilter.java

@@ -0,0 +1,40 @@
+package org.springframework.batch.execution.repository.dao;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
+import org.springframework.batch.core.domain.JobInstance;
+import org.springframework.batch.core.runtime.JobIdentifier;
+
+/**
+ * Shared utility class for {@link JobDao} implementations to allow a
+ * {@link JobInstance} to be identified from its {@link JobIdentifier}.
+ * 
+ * @author Dave Syer
+ * 
+ */
+class JobInstanceFilter {
+
+	/**
+	 * Filter the list and pull out a {@link JobInstance} with the supplied
+	 * identifier.
+	 * 
+	 * @param instances
+	 *            a collection of {@link JobInstance}
+	 * @param identifier
+	 *            the required {@link JobIdentifier}
+	 * @return another collection of {@link JobInstance}, all matching the the
+	 *         given {@link JobIdentifier}
+	 */
+	public List filter(List instances, JobIdentifier identifier) {
+		List result = new ArrayList();
+		for (Iterator iterator = instances.iterator(); iterator.hasNext();) {
+			JobInstance job = (JobInstance) iterator.next();
+			if (job.getIdentifier().equals(identifier)) {
+				result.add(job);
+			}
+		}
+		return result;
+	}
+}