Optimize findJobExecutions to reuse provided JobInstance

Author: l2yujw

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/jdbc/JdbcJobExecutionDao.java

@@ -218,12 +218,17 @@ public List<JobExecution> findJobExecutions(final JobInstance jobInstance) {
 
 		Assert.notNull(jobInstance, "Job instance cannot be null.");
 		long jobInstanceId = jobInstance.getId();
-		// TODO optimize to a single query with a join if possible
-		List<Long> jobExecutionIdsSortedBackwardByCreationOrder = getJdbcTemplate()
-			.queryForList(getQuery(GET_JOB_EXECUTION_IDS_BY_INSTANCE_ID), Long.class, jobInstanceId);
-		List<JobExecution> jobExecutions = new ArrayList<>(jobExecutionIdsSortedBackwardByCreationOrder.size());
-		for (Long jobExecutionId : jobExecutionIdsSortedBackwardByCreationOrder) {
-			jobExecutions.add(getJobExecution(jobExecutionId));
+
+		// TODO Further reduce database round-trips by retrieving executions and parameters in fewer queries.
+		List<Long> executionIds = getJdbcTemplate()
+				.queryForList(getQuery(GET_JOB_EXECUTION_IDS_BY_INSTANCE_ID), Long.class, jobInstanceId);
+
+		List<JobExecution> jobExecutions = new ArrayList<>(executionIds.size());
+		for (Long executionId : executionIds) {
+			JobExecution jobExecution = mapJobExecution(executionId, jobInstance);
+			if (jobExecution != null) {
+				jobExecutions.add(jobExecution);
+			}
 		}
 		return jobExecutions;
 	}
@@ -336,6 +341,17 @@ private long getJobInstanceId(long jobExecutionId) {
 				jobExecutionId);
 	}
 
+	private JobExecution mapJobExecution(long executionId, JobInstance jobInstance) {
+		JobParameters jobParameters = getJobParameters(executionId);
+		try {
+			return getJdbcTemplate().queryForObject(getQuery(GET_EXECUTION_BY_ID),
+					new JobExecutionRowMapper(jobInstance, jobParameters), executionId);
+		}
+		catch (EmptyResultDataAccessException ex) {
+			return null;
+		}
+	}
+
 	@Override
 	public Set<JobExecution> findRunningJobExecutions(String jobName) {
 		return getJdbcTemplate().queryForList(getQuery(GET_RUNNING_EXECUTION_FOR_INSTANCE), Long.class, jobName)