HHH-13675 : Optimize PersistentBag.groupByEqualityHash()

Author: dreis2211

hibernate-core/src/main/java/org/hibernate/collection/internal/PersistentBag.java

@@ -11,11 +11,12 @@
 import java.sql.SQLException;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
 import java.util.ListIterator;
 import java.util.Map;
-import java.util.stream.Collectors;
 
 import org.hibernate.HibernateException;
 import org.hibernate.engine.spi.SessionImplementor;
@@ -193,7 +194,14 @@ public boolean equalsSnapshot(CollectionPersister persister) throws HibernateExc
  * @return Map of "equality" hashCode to List of objects
  */
 private Map<Integer, List<Object>> groupByEqualityHash(List<Object> searchedBag, Type elementType) {
-return searchedBag.stream().collect( Collectors.groupingBy( elementType::getHashCode ) );
+if ( searchedBag.isEmpty() ) {
+return Collections.emptyMap();
+}
+Map<Integer, List<Object>> map = new HashMap<>();
+for (Object o : searchedBag) {
+map.computeIfAbsent( elementType.getHashCode( o ), k -> new ArrayList<>() ).add( o );
+}
+return map;
 }
 
 @Override