HSEARCH-2920 Correctly handle session closing in BeforeChunkBatchlet

The stop() method will not be called systematically at the end, it will
just be called when the user explicitly requests to stop the job.
So we should take care of closing the session through other means.

jsr352/core/src/main/java/org/hibernate/search/jsr352/massindexing/impl/steps/beforechunk/BeforeChunkBatchlet.java

@@ -21,6 +21,7 @@
 import org.hibernate.search.jsr352.massindexing.impl.JobContextData;
 import org.hibernate.search.jsr352.massindexing.impl.util.PersistenceUtil;
 import org.hibernate.search.jsr352.massindexing.impl.util.SerializationUtil;
+import org.hibernate.search.util.impl.Closer;
 import org.hibernate.search.util.logging.impl.LoggerFactory;
 
 import static org.hibernate.search.jsr352.massindexing.MassIndexingJobParameters.OPTIMIZE_AFTER_PURGE;
@@ -50,9 +51,6 @@ public class BeforeChunkBatchlet extends AbstractBatchlet {
 	@BatchProperty(name = MassIndexingJobParameters.TENANT_ID)
 	private String tenantId;
 
-	private Session session;
-	private FullTextSession fts;
-
 	@Override
 	public String process() throws Exception {
 		boolean purgeAllOnStart = SerializationUtil.parseBooleanParameter( PURGE_ALL_ON_START, serializedPurgeAllOnStart );
@@ -61,20 +59,16 @@ public String process() throws Exception {
 		if ( purgeAllOnStart ) {
 			JobContextData jobData = (JobContextData) jobContext.getTransientUserData();
 			EntityManagerFactory emf = jobData.getEntityManagerFactory();
-			session = PersistenceUtil.openSession( emf, tenantId );
-			fts = Search.getFullTextSession( session );
-			jobData.getEntityTypes().forEach( clz -> fts.purgeAll( clz ) );
+			try (Session session = PersistenceUtil.openSession( emf, tenantId )) {
+				FullTextSession fts = Search.getFullTextSession( session );
+				jobData.getEntityTypes().forEach( clz -> fts.purgeAll( clz ) );
 
-			if ( optimizeAfterPurge ) {
-				log.startOptimization();
-				ContextHelper.getSearchIntegrator( session ).optimize();
+				if ( optimizeAfterPurge ) {
+					log.startOptimization();
+					ContextHelper.getSearchIntegrator( session ).optimize();
+				}
 			}
 		}
 		return null;
 	}
-
-	@Override
-	public void stop() throws Exception {
-		session.close();
-	}
 }