HHH-18976 Get rid of dynamic array instantiation in MultiEntityLoaderStandard

MultiEntityLoaderStandard is used for arbitrary ID types, including IdClass,
making it very problematic to instantiate T[] where T is the ID type:
in native images, it requires registering T[] for reflection for every T
that can possibly be used as an ID type.

Fortunately, MultiEntityLoaderStandard does not, in fact, need
concrete-type arrays: Object[] works perfectly well with this
implementation, and only the other implementation,
MultiIdEntityLoaderArrayParam, actually needs concrete-type arrays.
We're truly in a lucky streak, because MultiIdEntityLoaderArrayParam is
only used for well-known, basic types such as Integer, which can easily
be registered for reflection in native images, and likely will be for
other reasons anyway.

Some of the dynamic instantiations were originally introduced to fix
the following issue:

* HHH-17201 -- tested in MultiIdEntityLoadTests

The corresponding tests still pass after removing these dynamic array
instantiations.

Author: yrodiere

hibernate-core/src/main/java/org/hibernate/internal/MultiIdentifierLoadAccessImpl.java

@@ -19,7 +19,6 @@
 import org.hibernate.graph.GraphSemantic;
 import org.hibernate.graph.RootGraph;
 import org.hibernate.graph.spi.RootGraphImplementor;
-import org.hibernate.loader.ast.internal.LoaderHelper;
 import org.hibernate.persister.entity.EntityPersister;
 import org.hibernate.loader.ast.spi.MultiIdLoadOptions;
 
@@ -191,7 +190,7 @@ public <K> List<T> multiLoad(List<K> ids) {
 		}
 		else {
 			return perform( () -> (List<T>) entityPersister.multiLoad(
-					ids.toArray( LoaderHelper.createTypedArray( ids.get( 0 ).getClass(), ids.size() ) ),
+					ids.toArray( new Object[0] ),
 					session,
 					this
 			) );

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/AbstractMultiIdEntityLoader.java

@@ -11,7 +11,6 @@
 import org.hibernate.engine.spi.EntityKey;
 import org.hibernate.engine.spi.SessionFactoryImplementor;
 import org.hibernate.event.spi.EventSource;
-import org.hibernate.internal.build.AllowReflection;
 import org.hibernate.loader.ast.spi.MultiIdEntityLoader;
 import org.hibernate.loader.ast.spi.MultiIdLoadOptions;
 import org.hibernate.loader.internal.CacheLoadHelper.PersistenceContextEntry;
@@ -22,7 +21,6 @@
 import org.hibernate.sql.exec.spi.JdbcSelectExecutor;
 import org.hibernate.type.descriptor.java.JavaType;
 
-import java.lang.reflect.Array;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -40,15 +38,12 @@
 public abstract class AbstractMultiIdEntityLoader<T> implements MultiIdEntityLoader<T> {
 	private final EntityMappingType entityDescriptor;
 	private final SessionFactoryImplementor sessionFactory;
-	private final EntityIdentifierMapping identifierMapping;
-	protected final Object[] idArray;
+	protected final EntityIdentifierMapping identifierMapping;
 
-	@AllowReflection
 	public AbstractMultiIdEntityLoader(EntityMappingType entityDescriptor, SessionFactoryImplementor sessionFactory) {
 		this.entityDescriptor = entityDescriptor;
 		this.sessionFactory = sessionFactory;
 		identifierMapping = getLoadable().getIdentifierMapping();
-		idArray = (Object[]) Array.newInstance( identifierMapping.getJavaType().getJavaTypeClass(), 0 );
 	}
 
 	protected EntityMappingType getEntityDescriptor() {
@@ -303,10 +298,13 @@ else if ( unresolvedIds.size() == ids.length ) {
 		}
 		else {
 			// we need to load only some the ids
-			return unresolvedIds.toArray( idArray );
+			return toIdArray( unresolvedIds );
 		}
 	}
 
+	// Depending on the implementation, a specific subtype of Object[] (e.g. Integer[]) may be needed.
+	protected abstract Object[] toIdArray(List<Object> ids);
+
 	private boolean isIdCoercionEnabled() {
 		return !getSessionFactory().getJpaMetamodel().getJpaCompliance().isLoadByIdComplianceEnabled();
 	}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/MultiIdEntityLoaderArrayParam.java

@@ -4,6 +4,8 @@
  */
 package org.hibernate.loader.ast.internal;
 
+import java.lang.reflect.Array;
+import java.util.Arrays;
 import java.util.List;
 
 import org.hibernate.LockOptions;
@@ -12,6 +14,7 @@
 import org.hibernate.engine.spi.PersistenceContext;
 import org.hibernate.engine.spi.SessionFactoryImplementor;
 import org.hibernate.event.spi.EventSource;
+import org.hibernate.internal.build.AllowReflection;
 import org.hibernate.loader.ast.spi.MultiIdLoadOptions;
 import org.hibernate.loader.ast.spi.SqlArrayMultiKeyLoader;
 import org.hibernate.metamodel.mapping.BasicEntityIdentifierMapping;
@@ -44,12 +47,15 @@
 public class MultiIdEntityLoaderArrayParam<E> extends AbstractMultiIdEntityLoader<E> implements SqlArrayMultiKeyLoader {
 	private final JdbcMapping arrayJdbcMapping;
 	private final JdbcParameter jdbcParameter;
+	protected final Object[] idArray;
 
+	@AllowReflection
 	public MultiIdEntityLoaderArrayParam(
 			EntityMappingType entityDescriptor,
 			SessionFactoryImplementor sessionFactory) {
 		super( entityDescriptor, sessionFactory );
-		final Class<?> idClass = idArray.getClass().getComponentType();
+		final Class<?> idClass = identifierMapping.getJavaType().getJavaTypeClass();
+		idArray = (Object[]) Array.newInstance( idClass, 0 );
 		arrayJdbcMapping = resolveArrayJdbcMapping(
 				getIdentifierMapping().getJdbcMapping(),
 				idClass,
@@ -117,7 +123,7 @@ protected void loadEntitiesById(
 
 		final JdbcParameterBindings jdbcParameterBindings = new JdbcParameterBindingsImpl(1);
 		jdbcParameterBindings.addBinding( jdbcParameter,
-				new JdbcParameterBindingImpl( arrayJdbcMapping, idsInBatch.toArray( idArray ) ) );
+				new JdbcParameterBindingImpl( arrayJdbcMapping, toIdArray( idsInBatch ) ) );
 
 		getJdbcSelectExecutor().executeQuery(
 				getSqlAstTranslatorFactory().buildSelectTranslator( getSessionFactory(), sqlAst )
@@ -165,7 +171,7 @@ protected void loadEntitiesWithUnresolvedIds(
 						.translate( NO_BINDINGS, QueryOptions.NONE );
 
 		final List<E> databaseResults = loadByArrayParameter(
-				unresolvableIds,
+				toIdArray( unresolvableIds ),
 				sqlAst,
 				jdbcSelectOperation,
 				jdbcParameter,
@@ -189,4 +195,19 @@ protected void loadEntitiesWithUnresolvedIds(
 		}
 	}
 
+	@Override
+	protected Object[] toIdArray(List<Object> ids) {
+		return ids.toArray( idArray );
+	}
+
+	protected Object[] toIdArray(Object[] ids) {
+		if ( ids.getClass().equals( idArray.getClass() ) ) {
+			return ids;
+		}
+		else {
+			Object[] typedIdArray = Arrays.copyOf( idArray, ids.length );
+			System.arraycopy( ids, 0, typedIdArray, 0, ids.length );
+			return typedIdArray;
+		}
+	}
 }

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/MultiIdEntityLoaderStandard.java

@@ -218,4 +218,10 @@ protected void loadEntitiesWithUnresolvedIds(
 			idPosition += batchSize;
 		}
 	}
+
+	@Override
+	protected Object[] toIdArray(List<Object> ids) {
+		// This loader implementation doesn't need arrays to have a specific type, Object[] will do.
+		return ids.toArray( new Object[0] );
+	}
 }