Introduce standard DtoInstantiatingConverter.

Move simple Spring Converter implementation that allow to create DTOs from a source object previously copied amongst a variety of store modules.

Issue #2476.

Author: odrotbohm

src/main/java/org/springframework/data/convert/DtoInstantiatingConverter.java

@@ -0,0 +1,112 @@
+/*
+ * Copyright 2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.convert;
+
+import org.springframework.core.convert.converter.Converter;
+import org.springframework.data.mapping.Parameter;
+import org.springframework.data.mapping.PersistentEntity;
+import org.springframework.data.mapping.PersistentProperty;
+import org.springframework.data.mapping.SimplePropertyHandler;
+import org.springframework.data.mapping.context.MappingContext;
+import org.springframework.data.mapping.model.EntityInstantiator;
+import org.springframework.data.mapping.model.EntityInstantiators;
+import org.springframework.data.mapping.model.ParameterValueProvider;
+import org.springframework.lang.NonNull;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
+/**
+ * Spring {@link Converter} to create instances of the given DTO type from the source value handed into the conversion.
+ *
+ * @author Mark Paluch
+ * @author Oliver Drotbohm
+ * @since 2.7
+ */
+public class DtoInstantiatingConverter implements Converter<Object, Object> {
+
+	private final Class<?> targetType;
+	private final MappingContext<? extends PersistentEntity<?, ?>, ? extends PersistentProperty<?>> context;
+	private final EntityInstantiator instantiator;
+
+	/**
+	 * Create a new {@link Converter} to instantiate DTOs.
+	 *
+	 * @param dtoType must not be {@literal null}.
+	 * @param context must not be {@literal null}.
+	 * @param instantiators must not be {@literal null}.
+	 */
+	public DtoInstantiatingConverter(Class<?> dtoType,
+			MappingContext<? extends PersistentEntity<?, ?>, ? extends PersistentProperty<?>> context,
+			EntityInstantiators instantiators) {
+
+		Assert.notNull(dtoType, "DTO type must not be null!");
+		Assert.notNull(context, "MappingContext must not be null!");
+		Assert.notNull(instantiators, "EntityInstantiators must not be null!");
+
+		this.targetType = dtoType;
+		this.context = context;
+		this.instantiator = instantiators.getInstantiatorFor(context.getRequiredPersistentEntity(dtoType));
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.core.convert.converter.Converter#convert(java.lang.Object)
+	 */
+	@NonNull
+	@Override
+	public Object convert(Object source) {
+
+		if (targetType.isInterface()) {
+			return source;
+		}
+
+		var sourceEntity = context.getRequiredPersistentEntity(source.getClass());
+		var sourceAccessor = sourceEntity.getPropertyAccessor(source);
+		var targetEntity = context.getRequiredPersistentEntity(targetType);
+
+		@SuppressWarnings({ "rawtypes", "unchecked" })
+		var dto = instantiator.createInstance(targetEntity, new ParameterValueProvider() {
+
+			@Override
+			@Nullable
+			public Object getParameterValue(Parameter parameter) {
+
+				var name = parameter.getName();
+
+				if (name == null) {
+					throw new IllegalArgumentException(String.format("Parameter %s does not have a name", parameter));
+				}
+
+				return sourceAccessor.getProperty(sourceEntity.getRequiredPersistentProperty(name));
+			}
+		});
+
+		var targetAccessor = targetEntity.getPropertyAccessor(dto);
+		var creator = targetEntity.getInstanceCreatorMetadata();
+
+		targetEntity.doWithProperties((SimplePropertyHandler) property -> {
+
+			if ((creator != null) && creator.isCreatorParameter(property)) {
+				return;
+			}
+
+			targetAccessor.setProperty(property,
+					sourceAccessor.getProperty(sourceEntity.getRequiredPersistentProperty(property.getName())));
+		});
+
+		return dto;
+	}
+}