GH-2304: Fix SendTo on Interface Etc.

Resolves #2304

`@SendTo` was only detected on the concrete listener method.

Use `AnnotatedElementUtils.findMergedAnnotation()` instead.

**cherry-pick to 2.9.x, 2.8.x**

Author: garyrussell

Diff for: spring-kafka/src/main/java/org/springframework/kafka/config/MethodKafkaListenerEndpoint.java

@@ -25,7 +25,7 @@
 import org.springframework.beans.factory.config.BeanExpressionContext;
 import org.springframework.beans.factory.config.BeanExpressionResolver;
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
-import org.springframework.core.annotation.AnnotationUtils;
+import org.springframework.core.annotation.AnnotatedElementUtils;
 import org.springframework.core.log.LogAccessor;
 import org.springframework.expression.BeanResolver;
 import org.springframework.kafka.listener.KafkaListenerErrorHandler;
@@ -132,7 +132,7 @@ public void setMessagingConverter(SmartMessageConverter messagingConverter) {
 	private String getReplyTopic() {
 		Method replyingMethod = getMethod();
 		if (replyingMethod != null) {
-			SendTo ann = AnnotationUtils.getAnnotation(replyingMethod, SendTo.class);
+			SendTo ann = AnnotatedElementUtils.findMergedAnnotation(replyingMethod, SendTo.class);
 			if (ann != null) {
 				if (replyingMethod.getReturnType().equals(void.class)) {
 					this.logger.warn(() -> "Method "

Diff for: spring-kafka/src/main/java/org/springframework/kafka/listener/adapter/DelegatingInvocableHandler.java

@@ -31,7 +31,7 @@
 import org.springframework.beans.factory.config.BeanExpressionResolver;
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
 import org.springframework.core.MethodParameter;
-import org.springframework.core.annotation.AnnotationUtils;
+import org.springframework.core.annotation.AnnotatedElementUtils;
 import org.springframework.expression.Expression;
 import org.springframework.expression.spel.standard.SpelExpressionParser;
 import org.springframework.kafka.KafkaException;
@@ -228,12 +228,12 @@ private void setupReplyTo(InvocableHandlerMethod handler) {
 		Method method = handler.getMethod();
 		SendTo ann = null;
 		if (method != null) {
-			ann = AnnotationUtils.getAnnotation(method, SendTo.class);
+			ann = AnnotatedElementUtils.findMergedAnnotation(method, SendTo.class);
 			replyTo = extractSendTo(method.toString(), ann);
 		}
 		if (ann == null) {
 			Class<?> beanType = handler.getBeanType();
-			ann = AnnotationUtils.getAnnotation(beanType, SendTo.class);
+			ann = AnnotatedElementUtils.findMergedAnnotation(beanType, SendTo.class);
 			replyTo = extractSendTo(beanType.getSimpleName(), ann);
 		}
 		if (ann != null && replyTo == null) {

Diff for: spring-kafka/src/test/java/org/springframework/kafka/annotation/EnableKafkaIntegrationTests.java

@@ -184,7 +184,8 @@
 		"annotated25", "annotated25reply1", "annotated25reply2", "annotated26", "annotated27", "annotated28",
 		"annotated29", "annotated30", "annotated30reply", "annotated31", "annotated32", "annotated33",
 		"annotated34", "annotated35", "annotated36", "annotated37", "foo", "manualStart", "seekOnIdle",
-		"annotated38", "annotated38reply", "annotated39", "annotated40", "annotated41", "annotated42" })
+		"annotated38", "annotated38reply", "annotated39", "annotated40", "annotated41", "annotated42",
+		"annotated43", "annotated43reply"})
 @TestPropertySource(properties = "spel.props=fetch.min.bytes=420000,max.poll.records=10")
 public class EnableKafkaIntegrationTests {
 
@@ -438,6 +439,15 @@ public void testInterface() throws Exception {
 		template.send("annotated7", 0, "foo");
 		template.flush();
 		assertThat(this.ifaceListener.getLatch1().await(60, TimeUnit.SECONDS)).isTrue();
+		Map<String, Object> consumerProps = new HashMap<>(this.consumerFactory.getConfigurationProperties());
+		consumerProps.put(ConsumerConfig.GROUP_ID_CONFIG, "testInterface");
+		ConsumerFactory<Integer, String> cf = new DefaultKafkaConsumerFactory<>(consumerProps);
+		Consumer<Integer, String> consumer = cf.createConsumer();
+		this.embeddedKafka.consumeFromAnEmbeddedTopic(consumer, "annotated43reply");
+		template.send("annotated43", 0, "foo");
+		ConsumerRecord<Integer, String> reply = KafkaTestUtils.getSingleRecord(consumer, "annotated43reply");
+		assertThat(reply).extracting(rec -> rec.value()).isEqualTo("FOO");
+		consumer.close();
 	}
 
 	@Test
@@ -1375,8 +1385,8 @@ public MultiListenerNoDefault multiNoDefault() {
 		}
 
 		@Bean
-		public MultiListenerSendTo multiListenerSendTo() {
-			return new MultiListenerSendTo();
+		public MultiListenerSendToImpl multiListenerSendTo() {
+			return new MultiListenerSendToImpl();
 		}
 
 		@Bean
@@ -2290,6 +2300,10 @@ interface IfaceListener<T> {
 
 		void listen(T foo);
 
+		@SendTo("annotated43reply")
+		@KafkaListener(id = "ifcR", topics = "annotated43")
+		String reply(String in);
+
 	}
 
 	static class IfaceListenerImpl implements IfaceListener<String> {
@@ -2310,6 +2324,11 @@ public void listenTx(String foo) {
 			latch2.countDown();
 		}
 
+		@Override
+		public String reply(String in) {
+			return in.toUpperCase();
+		}
+
 		public CountDownLatch getLatch1() {
 			return latch1;
 		}
@@ -2416,15 +2435,25 @@ public void bar(@Valid ValidatedClass val) {
 
 	@KafkaListener(id = "multiSendTo", topics = "annotated25")
 	@SendTo("annotated25reply1")
-	static class MultiListenerSendTo {
+	interface MultiListenerSendTo {
+
+		@KafkaHandler
+		String foo(String in);
 
 		@KafkaHandler
+		@SendTo("!{'annotated25reply2'}")
+		String bar(KafkaNull nul, int key);
+
+	}
+
+	static class MultiListenerSendToImpl implements MultiListenerSendTo {
+
+		@Override
 		public String foo(String in) {
 			return in.toUpperCase();
 		}
 
-		@KafkaHandler
-		@SendTo("!{'annotated25reply2'}")
+		@Override
 		public String bar(@Payload(required = false) KafkaNull nul,
 				@Header(KafkaHeaders.RECEIVED_MESSAGE_KEY) int key) {
 			return "BAR";