Add FieldExtractor implementation for Java records

Resolves #4159

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/file/transform/RecordFieldExtractor.java

@@ -0,0 +1,101 @@
+/*
+ * 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.batch.item.file.transform;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.RecordComponent;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
+/**
+ * This is a field extractor for a Java record. By default, it will extract all record
+ * components, unless a subset is selected using {@link #setNames(String...)}.
+ *
+ * @author Mahmoud Ben Hassine
+ * @since 5.0
+ */
+public class RecordFieldExtractor<T> implements FieldExtractor<T> {
+
+	private List<String> names;
+
+	private Class<? extends T> targetType;
+
+	private RecordComponent[] recordComponents;
+
+	public RecordFieldExtractor(Class<? extends T> targetType) {
+		Assert.notNull(targetType, "target type must not be null");
+		Assert.isTrue(targetType.isRecord(), "target type must be a record");
+		this.targetType = targetType;
+		this.recordComponents = this.targetType.getRecordComponents();
+		this.names = getRecordComponentNames();
+	}
+
+	/**
+	 * Set the names of record components to extract.
+	 * @param names of record component to be extracted.
+	 */
+	public void setNames(String... names) {
+		Assert.notNull(names, "Names must not be null");
+		Assert.notEmpty(names, "Names must not be empty");
+		validate(names);
+		this.names = Arrays.stream(names).toList();
+	}
+
+	/**
+	 * @see FieldExtractor#extract(Object)
+	 */
+	@Override
+	public Object[] extract(T item) {
+		List<Object> values = new ArrayList<>();
+		for (String componentName : this.names) {
+			RecordComponent recordComponent = getRecordComponentByName(componentName);
+			Object value;
+			try {
+				value = recordComponent.getAccessor().invoke(item);
+				values.add(value);
+			}
+			catch (IllegalAccessException | InvocationTargetException e) {
+				throw new RuntimeException("Unable to extract value for record component " + componentName, e);
+			}
+		}
+		return values.toArray();
+	}
+
+	private List<String> getRecordComponentNames() {
+		return Arrays.stream(this.recordComponents).map(recordComponent -> recordComponent.getName()).toList();
+	}
+
+	private void validate(String[] names) {
+		for (String name : names) {
+			if (getRecordComponentByName(name) == null) {
+				throw new IllegalArgumentException(
+						"Component '" + name + "' is not defined in record " + targetType.getName());
+			}
+		}
+	}
+
+	@Nullable
+	private RecordComponent getRecordComponentByName(String name) {
+		return Arrays.stream(this.recordComponents).filter(recordComponent -> recordComponent.getName().equals(name))
+				.findFirst().orElse(null);
+	}
+
+}

spring-batch-infrastructure/src/test/java/org/springframework/batch/item/file/transform/RecordFieldExtractorTests.java

@@ -0,0 +1,85 @@
+/*
+ * 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.batch.item.file.transform;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * @author Mahmoud Ben Hassine
+ */
+public class RecordFieldExtractorTests {
+
+	@Test(expected = IllegalArgumentException.class)
+	public void testSetupWithNullTargetType() {
+		new RecordFieldExtractor<>(null);
+	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void testSetupWithNonRecordTargetType() {
+		new RecordFieldExtractor<>(NonRecordType.class);
+	}
+
+	@Test
+	public void testExtractFields() {
+		// given
+		RecordFieldExtractor<Person> recordFieldExtractor = new RecordFieldExtractor<>(Person.class);
+		Person person = new Person(1, "foo");
+
+		// when
+		Object[] fields = recordFieldExtractor.extract(person);
+
+		// then
+		Assert.assertNotNull(fields);
+		Assert.assertArrayEquals(new Object[] { 1, "foo" }, fields);
+	}
+
+	@Test
+	public void testExtractFieldsSubset() {
+		// given
+		RecordFieldExtractor<Person> recordFieldExtractor = new RecordFieldExtractor<>(Person.class);
+		recordFieldExtractor.setNames("name");
+		Person person = new Person(1, "foo");
+
+		// when
+		Object[] fields = recordFieldExtractor.extract(person);
+
+		// then
+		Assert.assertNotNull(fields);
+		Assert.assertArrayEquals(new Object[] { "foo" }, fields);
+	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void testInvalidComponentName() {
+		// given
+		RecordFieldExtractor<Person> recordFieldExtractor = new RecordFieldExtractor<>(Person.class);
+		recordFieldExtractor.setNames("nonExistent");
+		Person person = new Person(1, "foo");
+
+		// when
+		recordFieldExtractor.extract(person);
+
+		// then
+		// expected exception
+	}
+
+	public record Person(int id, String name) {
+	}
+
+	public class NonRecordType {
+	}
+
+}