Demonstrate @Publisher with an @EventListener (#8603)

* Demonstrate `@Publisher` with an `@EventListener`

The `@EventListener` from Spring Framework is a good tool for POJO configuration
to subscribe to events from an `ApplicationContext`.
The `@Publisher` is an AOP tool to publish a `Message` from POJO method call.

* Add a test and docs to demonstrate how the `@Publisher` can be used together with an `@EventListener`

* Add `@Publisher` with a `@RabbitListener` sample in docs

* * Fix FQCN for `@Queue` in the `AmqpTests`

spring-integration-amqp/src/test/java/org/springframework/integration/amqp/dsl/AmqpTests.java

@@ -31,6 +31,9 @@ import org.springframework.amqp.core.AnonymousQueue;
 import org.springframework.amqp.core.MessageDeliveryMode;
 import org.springframework.amqp.core.Queue;
 import org.springframework.amqp.rabbit.AsyncRabbitTemplate;
+import org.springframework.amqp.rabbit.annotation.EnableRabbit;
+import org.springframework.amqp.rabbit.annotation.RabbitListener;
+import org.springframework.amqp.rabbit.config.SimpleRabbitListenerContainerFactory;
 import org.springframework.amqp.rabbit.connection.CachingConnectionFactory;
 import org.springframework.amqp.rabbit.connection.ConnectionFactory;
 import org.springframework.amqp.rabbit.core.RabbitAdmin;
@@ -56,8 +59,10 @@ import org.springframework.integration.amqp.inbound.AmqpInboundGateway;
 import org.springframework.integration.amqp.support.AmqpHeaderMapper;
 import org.springframework.integration.amqp.support.AmqpMessageHeaderErrorMessageStrategy;
 import org.springframework.integration.amqp.support.DefaultAmqpHeaderMapper;
+import org.springframework.integration.annotation.Publisher;
 import org.springframework.integration.channel.QueueChannel;
 import org.springframework.integration.config.EnableIntegration;
+import org.springframework.integration.config.EnablePublisher;
 import org.springframework.integration.dsl.IntegrationFlow;
 import org.springframework.integration.dsl.IntegrationFlowBuilder;
 import org.springframework.integration.dsl.Transformers;
@@ -68,6 +73,7 @@ import org.springframework.integration.test.util.TestUtils;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageChannel;
 import org.springframework.messaging.PollableChannel;
+import org.springframework.messaging.handler.annotation.Payload;
 import org.springframework.rabbit.stream.listener.ConsumerCustomizer;
 import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
@@ -87,7 +93,7 @@ import static org.mockito.Mockito.verify;
 @SpringJUnitConfig
 @RabbitAvailable(queues = {"amqpOutboundInput", "amqpReplyChannel", "asyncReplies",
 		"defaultReplyTo", "si.dsl.test", "si.dsl.exception.test.dlq",
-		"si.dsl.conv.exception.test.dlq", "testTemplateChannelTransacted"})
+		"si.dsl.conv.exception.test.dlq", "testTemplateChannelTransacted", "publisherQueue"})
 @DirtiesContext
 public class AmqpTests {
 
@@ -282,8 +288,23 @@ public class AmqpTests {
 		verify(customizer).accept(any(), any());
 	}
 
+	@Autowired
+	QueueChannel fromRabbitViaPublisher;
+
+	@Test
+	void messageReceivedFromRabbitListenerViaPublisher() {
+		this.amqpTemplate.convertAndSend("publisherQueue", "test data");
+
+		Message<?> receive = this.fromRabbitViaPublisher.receive(10_000);
+		assertThat(receive).isNotNull()
+				.extracting(Message::getPayload)
+				.isEqualTo("TEST DATA");
+	}
+
 	@Configuration
 	@EnableIntegration
+	@EnableRabbit
+	@EnablePublisher
 	public static class ContextConfiguration {
 
 		@Bean
@@ -495,6 +516,27 @@ public class AmqpTests {
 			return DefaultAmqpHeaderMapper.outboundMapper();
 		}
 
+		@Bean
+		public SimpleRabbitListenerContainerFactory rabbitListenerContainerFactory(
+				ConnectionFactory rabbitConnectionFactory) {
+
+			SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
+			factory.setConnectionFactory(rabbitConnectionFactory);
+			return factory;
+		}
+
+		@Bean
+		QueueChannel fromRabbitViaPublisher() {
+			return new QueueChannel();
+		}
+
+		@RabbitListener(queuesToDeclare = @org.springframework.amqp.rabbit.annotation.Queue("publisherQueue"))
+		@Publisher("fromRabbitViaPublisher")
+		@Payload("#args.payload.toUpperCase()")
+		public void consumeForPublisher(String payload) {
+
+		}
+
 	}
 
 }

spring-integration-event/src/test/java/org/springframework/integration/event/dsl/IntegrationFlowEventsTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2022 the original author or authors.
+ * Copyright 2016-2023 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.
@@ -26,8 +26,11 @@ import org.springframework.context.ApplicationEvent;
 import org.springframework.context.ApplicationListener;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.context.event.EventListener;
+import org.springframework.integration.annotation.Publisher;
 import org.springframework.integration.channel.QueueChannel;
 import org.springframework.integration.config.EnableIntegration;
+import org.springframework.integration.config.EnablePublisher;
 import org.springframework.integration.core.GenericHandler;
 import org.springframework.integration.dsl.IntegrationFlow;
 import org.springframework.integration.dsl.MessageChannels;
@@ -84,6 +87,9 @@ public class IntegrationFlowEventsTests {
 	@Autowired
 	private ApplicationEvents applicationEvents;
 
+	@Autowired
+	QueueChannel eventFromPublisher;
+
 	@Test
 	public void testEventsFlow() {
 		assertThat(this.applicationEvents.stream(MessagingEvent.class)).isEmpty();
@@ -115,9 +121,17 @@ public class IntegrationFlowEventsTests {
 		assertThat(messageGroupStore.getMessageCountForAllMessageGroups()).isEqualTo(0);
 	}
 
+	@Test
+	public void eventFromPublisherAnnotation() {
+		this.applicationContext.publishEvent(new TestApplicationEvent3());
+		Message<?> receive = this.eventFromPublisher.receive(10000);
+		assertThat(receive).isNotNull()
+				.extracting(Message::getPayload).isEqualTo("TestApplicationEvent3");
+	}
 
 	@Configuration
 	@EnableIntegration
+	@EnablePublisher
 	public static class ContextConfiguration {
 
 		@Bean
@@ -176,6 +190,17 @@ public class IntegrationFlowEventsTests {
 					.channel(MessageChannels.queue("delayedResults"));
 		}
 
+		@Bean
+		QueueChannel eventFromPublisher() {
+			return new QueueChannel();
+		}
+
+		@EventListener
+		@Publisher("eventFromPublisher")
+		public String publishEventToChannel(TestApplicationEvent3 testApplicationEvent3) {
+			return testApplicationEvent3.getSource().toString();
+		}
+
 	}
 
 	@SuppressWarnings("serial")
@@ -196,4 +221,13 @@ public class IntegrationFlowEventsTests {
 
 	}
 
+	@SuppressWarnings("serial")
+	private static final class TestApplicationEvent3 extends ApplicationEvent {
+
+		TestApplicationEvent3() {
+			super("TestApplicationEvent3");
+		}
+
+	}
+
 }

src/reference/asciidoc/amqp.adoc

@@ -253,6 +253,39 @@ In that regard, it is more similar to the JMS message-driven channel adapter.
 Starting with version 5.5, the `AmqpInboundChannelAdapter` can be configured with an `org.springframework.amqp.rabbit.retry.MessageRecoverer` strategy which is used in the `RecoveryCallback` when the retry operation is called internally.
 See `setMessageRecoverer()` JavaDocs for more information.
 
+The `@Publisher` annotation also can be used in combination with a `@RabbitListener`:
+
+====
+[source, java]
+----
+@Configuration
+@EnableIntegration
+@EnableRabbit
+@EnablePublisher
+public static class ContextConfiguration {
+
+    @Bean
+    QueueChannel fromRabbitViaPublisher() {
+        return new QueueChannel();
+    }
+
+    @RabbitListener(queuesToDeclare = @Queue("publisherQueue"))
+    @Publisher("fromRabbitViaPublisher")
+    @Payload("#args.payload.toUpperCase()")
+    public void consumeForPublisher(String payload) {
+
+    }
+
+}
+----
+====
+
+By default, the `@Publisher` AOP interceptor deals with a return value from a method call.
+However, the return value from a `@RabbitListener` method is treated as an AMQP reply message.
+Therefore, such an approach cannot be used together with a `@Publisher`, so a `@Payload` annotation with respective SpEL expression against method arguments is a recommended way for this combination.
+See more information about the `@Publisher` in the <<./message-publishing.adoc#publisher-annotation, Annotation-driven Configuration>> section.
+
+
 [[amqp-debatching]]
 ==== Batched Messages
 

src/reference/asciidoc/event.adoc

@@ -177,3 +177,31 @@ public IntegrationFlow eventsOutFlow(ApplicationEventPublishingMessageHandler ev
 }
 ----
 ====
+
+The `@Publisher` annotation also can be used in combination with an `@EventListener`:
+
+====
+[source, java]
+----
+@Configuration
+@EnableIntegration
+@EnablePublisher
+public static class ContextConfiguration {
+
+     @Bean
+     QueueChannel eventFromPublisher() {
+         return new QueueChannel();
+     }
+
+     @EventListener
+     @Publisher("eventFromPublisher")
+     public String publishEventToChannel(TestApplicationEvent3 testApplicationEvent3) {
+         return testApplicationEvent3.getSource().toString();
+     }
+
+}
+----
+====
+
+In this case a return value of the event listener method is used as a payload for a `Message` to be published to that `eventFromPublisher` channel.
+See more information about the `@Publisher` in the <<./message-publishing.adoc#publisher-annotation, Annotation-driven Configuration>> section.