Add new methods to get the last job instance/execution in JobInstance/JobExecution DAOs

Before this commit, getting the last job instance/execution required to
load all job instances/executions from the database and filter them
on the client side in memory.

This commit introduces new methods that use database queries to get
the last job instance/execution without the need to load all job
instances/executions. This change improves memory consumption as well as
the performance of starting the next instance of a job.

Resolves BATCH-1784

spring-batch-core/src/test/java/org/springframework/batch/core/explore/support/SimpleJobExplorerTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2013 the original author or authors.
+ * Copyright 2006-2019 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.
@@ -42,6 +42,7 @@ import org.springframework.batch.core.repository.dao.StepExecutionDao;
  * @author Dave Syer
  * @author Will Schipp
  * @author Michael Minella
+ * @author Mahmoud Ben Hassine
  *
  */
 public class SimpleJobExplorerTests {
@@ -82,6 +83,13 @@ public class SimpleJobExplorerTests {
 		jobExplorer.getJobExecution(123L);
 	}
 
+	@Test
+	public void testGetLastJobExecution() {
+		when(jobExecutionDao.getLastJobExecution(jobInstance)).thenReturn(jobExecution);
+		JobExecution lastJobExecution = jobExplorer.getLastJobExecution(jobInstance);
+		assertEquals(jobExecution, lastJobExecution);
+	}
+
 	@Test
 	public void testMissingGetJobExecution() throws Exception {
 		when(jobExecutionDao.getJobExecution(123L)).thenReturn(null);
@@ -156,6 +164,13 @@ public class SimpleJobExplorerTests {
 		jobExplorer.getJobInstances("foo", 0, 1);
 	}
 
+	@Test
+	public void testGetLastJobInstance() {
+		when(jobInstanceDao.getLastJobInstance("foo")).thenReturn(jobInstance);
+		JobInstance lastJobInstance = jobExplorer.getLastJobInstance("foo");
+		assertEquals(jobInstance, lastJobInstance);
+	}
+
 	@Test
 	public void testGetJobNames() throws Exception {
 		jobInstanceDao.getJobNames();

spring-batch-core/src/test/java/org/springframework/batch/core/launch/support/CommandLineJobRunnerTests.java

@@ -505,6 +505,16 @@ public class CommandLineJobRunnerTests {
 			throw new UnsupportedOperationException();
 		}
 
+		@Override
+		public JobInstance getLastJobInstance(String jobName) {
+			return null;
+		}
+
+		@Override
+		public JobExecution getLastJobExecution(JobInstance jobInstance) {
+			return null;
+		}
+
 		@Override
 		public List<JobInstance> getJobInstances(String jobName, int start, int count) {
 			if (jobInstances == null) {

spring-batch-core/src/test/java/org/springframework/batch/core/repository/dao/AbstractJobInstanceDaoTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2008-2013 the original author or authors.
+ * Copyright 2008-2019 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.
@@ -154,6 +154,33 @@ public abstract class AbstractJobInstanceDaoTests {
 
 	}
 
+	@Transactional
+	@Test
+	public void testGetLastInstance() throws Exception {
+		testCreateAndRetrieve();
+
+		// unrelated job instance that should be ignored by the query
+		dao.createJobInstance("anotherJob", new JobParameters());
+
+		// we need two instances of the same job to check ordering
+		dao.createJobInstance(fooJob, new JobParameters());
+
+		List<JobInstance> jobInstances = dao.getJobInstances(fooJob, 0, 2);
+		assertEquals(2, jobInstances.size());
+		JobInstance lastJobInstance = dao.getLastJobInstance(fooJob);
+		assertNotNull(lastJobInstance);
+		assertEquals(fooJob, lastJobInstance.getJobName());
+		assertEquals("Last instance should be first on the list",
+				jobInstances.get(0), lastJobInstance);
+	}
+
+	@Transactional
+	@Test
+	public void testGetLastInstanceWhenNoInstance() {
+		JobInstance lastJobInstance = dao.getLastJobInstance("NonExistingJob");
+		assertNull(lastJobInstance);
+	}
+
 	/**
 	 * Create and retrieve a job instance.
 	 */