[FSTORE-1628][APPEND] dont instantiate hudi when not necessary

java/spark/src/main/java/com/logicalclocks/hsfs/spark/engine/FeatureGroupEngine.java

@@ -52,8 +52,6 @@
 
 public class FeatureGroupEngine  extends FeatureGroupEngineBase {
 
-  private HudiEngine hudiEngine = new HudiEngine();
-
   /**
    * Create the metadata and write the data to the online/offline feature store.
    *
@@ -457,8 +455,8 @@ public FeatureGroupCommit commitDelete(FeatureGroupBase featureGroupBase, Datase
       throw new FeatureStoreException("delete function is only valid for "
           + "time travel enabled feature group");
     }
-    return hudiEngine.deleteRecord(SparkEngine.getInstance().getSparkSession(), featureGroupBase, genericDataset,
-        writeOptions);
+    return HudiEngine.getInstance().deleteRecord(SparkEngine.getInstance().getSparkSession(), featureGroupBase,
+        genericDataset, writeOptions);
   }
 
   public ExternalFeatureGroup saveExternalFeatureGroup(ExternalFeatureGroup externalFeatureGroup)

java/spark/src/main/java/com/logicalclocks/hsfs/spark/engine/SparkEngine.java

@@ -142,8 +142,6 @@ public static void setInstance(SparkEngine sparkEngine) {
   @Getter
   private SparkSession sparkSession;
 
-  private HudiEngine hudiEngine = new HudiEngine();
-
   private SparkEngine() {
     sparkSession = SparkSession.builder()
         .enableHiveSupport()
@@ -247,7 +245,7 @@ private Map<String, String> getOnDemandOptions(ExternalFeatureGroup externalFeat
 
   public void registerHudiTemporaryTable(FeatureGroupAlias featureGroupAlias, Map<String, String> readOptions)
           throws FeatureStoreException {
-    Map<String, String> hudiArgs = hudiEngine.setupHudiReadOpts(
+    Map<String, String> hudiArgs = HudiEngine.getInstance().setupHudiReadOpts(
         featureGroupAlias.getLeftFeatureGroupStartTimestamp(),
         featureGroupAlias.getLeftFeatureGroupEndTimestamp(),
         readOptions);
@@ -258,7 +256,7 @@ public void registerHudiTemporaryTable(FeatureGroupAlias featureGroupAlias, Map<
         .load(featureGroupAlias.getFeatureGroup().getLocation())
         .createOrReplaceTempView(featureGroupAlias.getAlias());
 
-    hudiEngine.reconcileHudiSchema(sparkSession, featureGroupAlias, hudiArgs);
+    HudiEngine.getInstance().reconcileHudiSchema(sparkSession, featureGroupAlias, hudiArgs);
   }
 
   /**
@@ -661,7 +659,8 @@ public void writeOfflineDataframe(FeatureGroupBase featureGroup, Dataset<Row> da
       throws IOException, FeatureStoreException, ParseException {
 
     if (featureGroup.getTimeTravelFormat() == TimeTravelFormat.HUDI) {
-      hudiEngine.saveHudiFeatureGroup(sparkSession, featureGroup, dataset, operation, writeOptions, validationId);
+      HudiEngine.getInstance().saveHudiFeatureGroup(sparkSession, featureGroup, dataset, operation,
+          writeOptions, validationId);
     } else {
       writeSparkDataset(featureGroup, dataset, writeOptions);
     }
@@ -790,7 +789,7 @@ private void setupAdlsConnectorHadoopConf(StorageConnector.AdlsConnector storage
   public void streamToHudiTable(StreamFeatureGroup streamFeatureGroup, Map<String, String> writeOptions)
       throws Exception {
     writeOptions = getKafkaConfig(streamFeatureGroup, writeOptions);
-    hudiEngine.streamToHoodieTable(sparkSession, streamFeatureGroup, writeOptions);
+    HudiEngine.getInstance().streamToHoodieTable(sparkSession, streamFeatureGroup, writeOptions);
   }
 
   public List<Feature> parseFeatureGroupSchema(Dataset<Row> dataset,

java/spark/src/main/java/com/logicalclocks/hsfs/spark/engine/hudi/HudiEngine.java

@@ -25,9 +25,7 @@
 import com.logicalclocks.hsfs.engine.FeatureGroupUtils;
 import com.logicalclocks.hsfs.metadata.FeatureGroupApi;
 import com.logicalclocks.hsfs.FeatureGroupBase;
-import com.logicalclocks.hsfs.metadata.KafkaApi;
 
-import com.logicalclocks.hsfs.metadata.StorageConnectorApi;
 import com.logicalclocks.hsfs.spark.FeatureGroup;
 import com.logicalclocks.hsfs.spark.FeatureStore;
 import com.logicalclocks.hsfs.spark.StreamFeatureGroup;
@@ -146,8 +144,19 @@ public class HudiEngine {
   private FeatureGroupApi featureGroupApi = new FeatureGroupApi();
   private FeatureGroupCommit fgCommitMetadata = new FeatureGroupCommit();
   private DeltaStreamerConfig deltaStreamerConfig = new DeltaStreamerConfig();
-  private KafkaApi kafkaApi = new KafkaApi();
-  private StorageConnectorApi storageConnectorApi = new StorageConnectorApi();
+
+  protected static HudiEngine INSTANCE = null;
+
+  public static synchronized HudiEngine getInstance() {
+    if (INSTANCE == null) {
+      INSTANCE = new HudiEngine();
+    }
+    return INSTANCE;
+  }
+
+  // To make sure everyone uses getInstance
+  private HudiEngine() {
+  }
 
   public void saveHudiFeatureGroup(SparkSession sparkSession, FeatureGroupBase featureGroup,
                                    Dataset<Row> dataset, HudiOperationType operation,

java/spark/src/test/java/com/logicalclocks/hsfs/spark/engine/TestHudiEngine.java

@@ -35,7 +35,7 @@ void testSparkSchemasMatch() throws Exception {
                 .add("name", "string")
                 .add("age", "int");
 
-        HudiEngine engine = new HudiEngine();
+        HudiEngine engine = HudiEngine.getInstance();
         Assertions.assertTrue(engine.sparkSchemasMatch(schema1.fieldNames(), schema2.fieldNames()));
     }
 
@@ -49,7 +49,7 @@ void testSparkSchemasMatchFeatureMissing() throws Exception {
                 .add("id", "int")
                 .add("name", "string");
 
-        HudiEngine engine = new HudiEngine();
+        HudiEngine engine = HudiEngine.getInstance();
         Assertions.assertFalse(engine.sparkSchemasMatch(schema1.fieldNames(), schema2.fieldNames()));
     }
 
@@ -64,7 +64,7 @@ void testSparkSchemasMatchDifferentOrder() throws Exception {
                 .add("age", "int")
                 .add("name", "string");
 
-        HudiEngine engine = new HudiEngine();
+        HudiEngine engine = HudiEngine.getInstance();
         Assertions.assertTrue(engine.sparkSchemasMatch(schema1.fieldNames(), schema2.fieldNames()));
     }