GH-4097: Fix SmartMessageConverter support in batch listeners

spring-kafka/src/main/java/org/springframework/kafka/listener/adapter/BatchMessagingMessageListenerAdapter.java

@@ -32,6 +32,7 @@
 import org.springframework.kafka.support.converter.BatchMessagingMessageConverter;
 import org.springframework.kafka.support.converter.RecordMessageConverter;
 import org.springframework.messaging.Message;
+import org.springframework.messaging.converter.SmartMessageConverter;
 import org.springframework.messaging.support.MessageBuilder;
 import org.springframework.util.Assert;
 
@@ -55,6 +56,7 @@
  * @author Venil Noronha
  * @author Wang ZhiYang
  * @author Sanghyeok An
+ * @author George Mahfoud
  * @since 1.1
  */
 public class BatchMessagingMessageListenerAdapter<K, V> extends MessagingMessageListenerAdapter<K, V>
@@ -107,6 +109,27 @@ public void setBatchToRecordAdapter(BatchToRecordAdapter<K, V> batchToRecordAdap
 		this.batchToRecordAdapter = batchToRecordAdapter;
 	}
 
+	/**
+	 * Set the {@link SmartMessageConverter} to use with the batch message converter.
+	 * <p>
+	 * When a {@code SmartMessageConverter} is configured via
+	 * {@code @KafkaListener(contentTypeConverter = "...")}, this method ensures it is
+	 * properly propagated to the batch converter, which will then propagate it to the
+	 * record converter for message conversion in batch listeners.
+	 * <p>
+	 * This override does not call the parent implementation because the parent's validation
+	 * (checking {@code converterSet}) blocks setting the SmartMessageConverter after
+	 * {@code setBatchMessageConverter} has been called, which is the normal workflow for
+	 * batch listeners.
+	 * @param messageConverter the converter to set
+	 */
+	@Override
+	public void setMessagingConverter(SmartMessageConverter messageConverter) {
+		if (this.batchMessageConverter instanceof BatchMessagingMessageConverter messagingConverter) {
+			messagingConverter.setMessagingConverter(messageConverter);
+		}
+	}
+
 	/**
 	 * Return the {@link BatchMessagingMessageConverter} for this listener,
 	 * being able to convert {@link org.springframework.messaging.Message}.

spring-kafka/src/main/java/org/springframework/kafka/support/converter/BatchMessagingMessageConverter.java

@@ -43,6 +43,7 @@
 import org.springframework.kafka.support.KafkaNull;
 import org.springframework.kafka.support.serializer.SerializationUtils;
 import org.springframework.messaging.Message;
+import org.springframework.messaging.converter.SmartMessageConverter;
 import org.springframework.messaging.support.MessageBuilder;
 
 /**
@@ -67,6 +68,7 @@
  * @author Borahm Lee
  * @author Artem Bilan
  * @author Soby Chacko
+ * @author George Mahfoud
  *
  * @since 1.1
  */
@@ -142,6 +144,18 @@ public RecordMessageConverter getRecordMessageConverter() {
 		return this.recordConverter;
 	}
 
+	/**
+	 * Set a spring-messaging {@link SmartMessageConverter} to convert the record value to
+	 * the desired type.
+	 * @param messagingConverter the converter.
+	 * @since 3.3.11
+	 */
+	public void setMessagingConverter(@Nullable SmartMessageConverter messagingConverter) {
+		if (this.recordConverter instanceof MessagingMessageConverter messagingRecordConverter) {
+			messagingRecordConverter.setMessagingConverter(messagingConverter);
+		}
+	}
+
 	/**
 	 * Set to true to add the raw {@code List<ConsumerRecord<?, ?>>} as a header
 	 * {@link KafkaHeaders#RAW_DATA}.
@@ -275,13 +289,14 @@ protected Object extractAndConvertValue(ConsumerRecord<?, ?> record, Type type)
 	 * @param type the type - must be a {@link ParameterizedType} with a single generic
 	 * type parameter.
 	 * @param conversionFailures Conversion failures.
-	 * @return the converted payload.
+	 * @return the converted payload, potentially further processed by a {@link SmartMessageConverter}.
 	 */
 	protected @Nullable Object convert(ConsumerRecord<?, ?> record, Type type, List<ConversionException> conversionFailures) {
 		try {
 			if (this.recordConverter != null) {
+				Type actualType = ((ParameterizedType) type).getActualTypeArguments()[0];
 				Object payload = this.recordConverter
-						.toMessage(record, null, null, ((ParameterizedType) type).getActualTypeArguments()[0]).getPayload();
+						.toMessage(record, null, null, actualType).getPayload();
 				conversionFailures.add(null);
 				return payload;
 			}

spring-kafka/src/test/java/org/springframework/kafka/listener/BatchSmartMessageConverterTests.java

@@ -0,0 +1,198 @@
+/*
+ * Copyright 2016-present 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.kafka.listener;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+import org.apache.kafka.clients.consumer.ConsumerConfig;
+import org.apache.kafka.clients.producer.ProducerConfig;
+import org.apache.kafka.common.serialization.ByteArrayDeserializer;
+import org.apache.kafka.common.serialization.ByteArraySerializer;
+import org.apache.kafka.common.serialization.IntegerDeserializer;
+import org.apache.kafka.common.serialization.IntegerSerializer;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.kafka.annotation.EnableKafka;
+import org.springframework.kafka.annotation.KafkaListener;
+import org.springframework.kafka.config.ConcurrentKafkaListenerContainerFactory;
+import org.springframework.kafka.config.KafkaListenerContainerFactory;
+import org.springframework.kafka.core.DefaultKafkaConsumerFactory;
+import org.springframework.kafka.core.DefaultKafkaProducerFactory;
+import org.springframework.kafka.core.KafkaTemplate;
+import org.springframework.kafka.core.ProducerFactory;
+import org.springframework.kafka.support.converter.BatchMessagingMessageConverter;
+import org.springframework.kafka.support.converter.MessagingMessageConverter;
+import org.springframework.kafka.test.EmbeddedKafkaBroker;
+import org.springframework.kafka.test.context.EmbeddedKafka;
+import org.springframework.kafka.test.utils.KafkaTestUtils;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.MessageHeaders;
+import org.springframework.messaging.converter.SmartMessageConverter;
+import org.springframework.messaging.support.MessageBuilder;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Integration tests for SmartMessageConverter support in batch listeners.
+ * Reproduces and verifies the fix for the issue described in GH-4097.
+ *
+ * @author George Mahfoud
+ * @since 3.3.11
+ */
+@SpringJUnitConfig
+@DirtiesContext
+@EmbeddedKafka(partitions = 1, topics = { "smartBatchTopic" })
+class BatchSmartMessageConverterTests {
+
+	@Autowired
+	private KafkaTemplate<Integer, byte[]> template;
+
+	@Autowired
+	private Config config;
+
+	@Test
+	void testContentTypeConverterWithBatchListener() throws Exception {
+		// Given: A batch listener with contentTypeConverter configured
+		BatchListener listener = this.config.batchListener();
+
+		// When: Send byte[] messages that should be converted to String
+		this.template.send("smartBatchTopic", "hello".getBytes());
+		this.template.send("smartBatchTopic", "world".getBytes());
+
+		// Then: SmartMessageConverter should convert byte[] to String for batch listener
+		assertThat(listener.latch.await(10, TimeUnit.SECONDS)).isTrue();
+		assertThat(listener.received).hasSize(2).containsExactly("hello", "world");
+	}
+
+	@Configuration
+	@EnableKafka
+	public static class Config {
+
+		@Bean
+		public KafkaListenerContainerFactory<?> kafkaListenerContainerFactory(EmbeddedKafkaBroker embeddedKafka) {
+			ConcurrentKafkaListenerContainerFactory<Integer, byte[]> factory =
+					new ConcurrentKafkaListenerContainerFactory<>();
+			factory.setConsumerFactory(consumerFactory(embeddedKafka));
+			factory.setBatchListener(true);
+			// Set up batch converter with record converter - framework will propagate SmartMessageConverter
+			factory.setBatchMessageConverter(new BatchMessagingMessageConverter(new MessagingMessageConverter()));
+			return factory;
+		}
+
+		@Bean
+		public DefaultKafkaConsumerFactory<Integer, byte[]> consumerFactory(EmbeddedKafkaBroker embeddedKafka) {
+			return new DefaultKafkaConsumerFactory<>(consumerConfigs(embeddedKafka));
+		}
+
+		@Bean
+		public Map<String, Object> consumerConfigs(EmbeddedKafkaBroker embeddedKafka) {
+			Map<String, Object> consumerProps =
+					KafkaTestUtils.consumerProps(embeddedKafka, "smartBatchGroup", false);
+			consumerProps.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, ByteArrayDeserializer.class);
+			consumerProps.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, IntegerDeserializer.class);
+			return consumerProps;
+		}
+
+		@Bean
+		public KafkaTemplate<Integer, byte[]> template(EmbeddedKafkaBroker embeddedKafka) {
+			return new KafkaTemplate<>(producerFactory(embeddedKafka));
+		}
+
+		@Bean
+		public ProducerFactory<Integer, byte[]> producerFactory(EmbeddedKafkaBroker embeddedKafka) {
+			return new DefaultKafkaProducerFactory<>(producerConfigs(embeddedKafka));
+		}
+
+		@Bean
+		public Map<String, Object> producerConfigs(EmbeddedKafkaBroker embeddedKafka) {
+			Map<String, Object> props = KafkaTestUtils.producerProps(embeddedKafka);
+			props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, ByteArraySerializer.class);
+			props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, IntegerSerializer.class);
+			return props;
+		}
+
+		@Bean
+		public SmartMessageConverter byteArrayToStringConverter() {
+			return new ByteArrayToStringConverter();
+		}
+
+		@Bean
+		public BatchListener batchListener() {
+			return new BatchListener();
+		}
+
+	}
+
+	public static class BatchListener {
+
+		private final CountDownLatch latch = new CountDownLatch(2);
+
+		private final List<String> received = new ArrayList<>();
+
+		@KafkaListener(
+				id = "batchSmartListener",
+				topics = "smartBatchTopic",
+				groupId = "smartBatchGroup",
+				contentTypeConverter = "byteArrayToStringConverter",
+				batch = "true"
+		)
+		public void listen(List<String> messages) {
+			messages.forEach(message -> {
+				this.received.add(message);
+				this.latch.countDown();
+			});
+		}
+
+	}
+
+	/**
+	 * Simple SmartMessageConverter for testing that converts byte[] to String.
+	 */
+	static class ByteArrayToStringConverter implements SmartMessageConverter {
+
+		@Override
+		public Object fromMessage(Message<?> message, Class<?> targetClass) {
+			Object payload = message.getPayload();
+			return (payload instanceof byte[] bytes) ? new String(bytes) : payload;
+		}
+
+		@Override
+		public Object fromMessage(Message<?> message, Class<?> targetClass, Object conversionHint) {
+			return fromMessage(message, targetClass);
+		}
+
+		@Override
+		public Message<?> toMessage(Object payload, MessageHeaders headers) {
+			return MessageBuilder.withPayload(payload).copyHeaders(headers).build();
+		}
+
+		@Override
+		public Message<?> toMessage(Object payload, MessageHeaders headers, Object conversionHint) {
+			return toMessage(payload, headers);
+		}
+
+	}
+}