GH-248 - Support to automatically externalize events.

We now allow externalizing application events to a variety of message brokers through the addition of Spring Modulith modules for Kafka, AMQP and JMS to a user project's classpath. Which events shall be externalized and how they're supposed to be routed to the message broker can be configured through either annotations or via a configuration API declared as Spring bean.

In case Jackson is on the classpath, we also add auto-configuration to use a Boot-configured ObjectMapper instance with the corresponding message broker client APIs to properly serialize and deserialize messages to JSON.

spring-modulith-bom/pom.xml

@@ -39,6 +39,11 @@
 				<artifactId>spring-modulith-docs</artifactId>
 				<version>1.1.0-SNAPSHOT</version>
 			</dependency>
+			<dependency>
+				<groupId>org.springframework.modulith</groupId>
+				<artifactId>spring-modulith-events-amqp</artifactId>
+				<version>1.1.0-SNAPSHOT</version>
+			</dependency>
 			<dependency>
 				<groupId>org.springframework.modulith</groupId>
 				<artifactId>spring-modulith-events-core</artifactId>
@@ -54,11 +59,21 @@
 				<artifactId>spring-modulith-events-jdbc</artifactId>
 				<version>1.1.0-SNAPSHOT</version>
 			</dependency>
+			<dependency>
+				<groupId>org.springframework.modulith</groupId>
+				<artifactId>spring-modulith-events-jms</artifactId>
+				<version>1.1.0-SNAPSHOT</version>
+			</dependency>
 			<dependency>
 				<groupId>org.springframework.modulith</groupId>
 				<artifactId>spring-modulith-events-jpa</artifactId>
 				<version>1.1.0-SNAPSHOT</version>
 			</dependency>
+			<dependency>
+				<groupId>org.springframework.modulith</groupId>
+				<artifactId>spring-modulith-events-kafka</artifactId>
+				<version>1.1.0-SNAPSHOT</version>
+			</dependency>
 			<dependency>
 				<groupId>org.springframework.modulith</groupId>
 				<artifactId>spring-modulith-events-mongodb</artifactId>

spring-modulith-events/pom.xml

@@ -14,12 +14,15 @@
 	<name>Spring Modulith - Events</name>
 
 	<modules>
+		<module>spring-modulith-events-amqp</module>
 		<module>spring-modulith-events-api</module>
 		<module>spring-modulith-events-core</module>
-		<module>spring-modulith-events-jpa</module>
+		<module>spring-modulith-events-jackson</module>
 		<module>spring-modulith-events-jdbc</module>
+		<module>spring-modulith-events-jms</module>
+		<module>spring-modulith-events-jpa</module>
+		<module>spring-modulith-events-kafka</module>
 		<module>spring-modulith-events-mongodb</module>
-		<module>spring-modulith-events-jackson</module>
 	</modules>
 
 	<profiles>

spring-modulith-events/spring-modulith-events-amqp/pom.xml

@@ -0,0 +1,92 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+
+	<modelVersion>4.0.0</modelVersion>
+
+	<parent>
+		<groupId>org.springframework.modulith</groupId>
+		<artifactId>spring-modulith-events</artifactId>
+		<version>1.1.0-SNAPSHOT</version>
+	</parent>
+
+	<name>Spring Modulith - Events - AMQP support</name>
+	<artifactId>spring-modulith-events-amqp</artifactId>
+
+	<properties>
+		<module.name>org.springframework.modulith.events.amqp</module.name>
+	</properties>
+
+	<dependencies>
+
+		<dependency>
+			<groupId>org.springframework.modulith</groupId>
+			<artifactId>spring-modulith-api</artifactId>
+			<version>${project.version}</version>
+		</dependency>
+
+		<dependency>
+			<groupId>org.springframework.modulith</groupId>
+			<artifactId>spring-modulith-events-core</artifactId>
+			<version>${project.version}</version>
+		</dependency>
+
+		<dependency>
+			<groupId>org.springframework.amqp</groupId>
+			<artifactId>spring-amqp</artifactId>
+		</dependency>
+
+		<dependency>
+			<groupId>org.springframework.amqp</groupId>
+			<artifactId>spring-rabbit</artifactId>
+			<optional>true</optional>
+		</dependency>
+
+		<dependency>
+			<groupId>com.fasterxml.jackson.core</groupId>
+			<artifactId>jackson-databind</artifactId>
+			<optional>true</optional>
+		</dependency>
+
+		<!-- Test dependencies -->
+
+		<dependency>
+			<groupId>org.springframework.modulith</groupId>
+			<artifactId>spring-modulith-starter-jdbc</artifactId>
+			<version>${project.version}</version>
+			<scope>test</scope>
+		</dependency>
+
+		<dependency>
+			<groupId>com.h2database</groupId>
+			<artifactId>h2</artifactId>
+			<scope>test</scope>
+		</dependency>
+
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-json</artifactId>
+			<scope>test</scope>
+		</dependency>
+
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-test</artifactId>
+			<scope>test</scope>
+		</dependency>
+
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-testcontainers</artifactId>
+			<scope>test</scope>
+		</dependency>
+
+		<dependency>
+			<groupId>org.testcontainers</groupId>
+			<artifactId>rabbitmq</artifactId>
+			<scope>test</scope>
+		</dependency>
+
+	</dependencies>
+
+</project>

spring-modulith-events/spring-modulith-events-amqp/src/main/java/org/springframework/modulith/events/amqp/RabbitEventExternalizerConfiguration.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright 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.
+ * 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.modulith.events.amqp;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.amqp.rabbit.core.RabbitMessageOperations;
+import org.springframework.amqp.rabbit.core.RabbitTemplate;
+import org.springframework.beans.factory.BeanFactory;
+import org.springframework.boot.autoconfigure.AutoConfiguration;
+import org.springframework.boot.autoconfigure.AutoConfigureAfter;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.expression.BeanFactoryResolver;
+import org.springframework.expression.spel.support.StandardEvaluationContext;
+import org.springframework.modulith.events.EventExternalizationConfiguration;
+import org.springframework.modulith.events.config.EventExternalizationAutoConfiguration;
+import org.springframework.modulith.events.support.BrokerRouting;
+import org.springframework.modulith.events.support.DelegatingEventExternalizer;
+
+/**
+ * Auto-configuration to set up a {@link DelegatingEventExternalizer} to externalize events to RabbitMQ.
+ *
+ * @author Oliver Drotbohm
+ * @since 1.1
+ */
+@AutoConfiguration
+@AutoConfigureAfter(EventExternalizationAutoConfiguration.class)
+@ConditionalOnClass(RabbitTemplate.class)
+class RabbitEventExternalizerConfiguration {
+
+	private static final Logger logger = LoggerFactory.getLogger(RabbitEventExternalizerConfiguration.class);
+
+	@Bean
+	DelegatingEventExternalizer rabbitEventExternalizer(EventExternalizationConfiguration configuration,
+			RabbitMessageOperations operations, BeanFactory factory) {
+
+		logger.debug("Registering domain event externalization to RabbitMQ…");
+
+		var context = new StandardEvaluationContext();
+		context.setBeanResolver(new BeanFactoryResolver(factory));
+
+		return new DelegatingEventExternalizer(configuration, (target, payload) -> {
+
+			var routing = BrokerRouting.of(target, context);
+
+			operations.convertAndSend(routing.getTarget(), routing.getKey(payload), payload);
+		});
+	}
+}

spring-modulith-events/spring-modulith-events-amqp/src/main/java/org/springframework/modulith/events/amqp/RabbitJacksonConfiguration.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright 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.
+ * 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.modulith.events.amqp;
+
+import org.springframework.amqp.rabbit.core.RabbitTemplate;
+import org.springframework.amqp.support.converter.Jackson2JsonMessageConverter;
+import org.springframework.boot.autoconfigure.AutoConfiguration;
+import org.springframework.boot.autoconfigure.amqp.RabbitTemplateCustomizer;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.context.annotation.Bean;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+/**
+ * Auto-configuration to configure {@link RabbitTemplate} to use the Jackson {@link ObjectMapper} present in the
+ * application.
+ *
+ * @author Oliver Drotbohm
+ * @since 1.1
+ */
+@AutoConfiguration
+@ConditionalOnClass({ RabbitTemplate.class, ObjectMapper.class })
+@ConditionalOnProperty(name = "spring.modulith.events.rabbitmq.enable-json", havingValue = "true",
+		matchIfMissing = true)
+class RabbitJacksonConfiguration {
+
+	@Bean
+	@ConditionalOnBean(ObjectMapper.class)
+	RabbitTemplateCustomizer rabbitTemplateCustomizer(ObjectMapper mapper) {
+
+		return template -> {
+			template.setMessageConverter(new Jackson2JsonMessageConverter(mapper));
+		};
+	}
+}

spring-modulith-events/spring-modulith-events-amqp/src/main/resources/META-INF/spring-configuration-metadata.json

@@ -0,0 +1,10 @@
+{
+	"properties": [
+		{
+			"name": "spring.modulith.events.rabbitmq.json-enabled",
+			"type": "java.lang.boolean",
+			"description": "Whether to auto-configure RabbitTemplate to use JSON for message serialization.",
+			"defaultValue": "true"
+		}
+	]
+}

spring-modulith-events/spring-modulith-events-amqp/src/main/resources/META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports

@@ -0,0 +1,2 @@
+org.springframework.modulith.events.amqp.RabbitEventExternalizerConfiguration
+org.springframework.modulith.events.amqp.RabbitJacksonConfiguration

spring-modulith-events/spring-modulith-events-amqp/src/test/java/org/springframework/modulith/events/amqp/RabbitEventPublicationIntegrationTests.java

@@ -0,0 +1,111 @@
+/*
+ * Copyright 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.
+ * 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.modulith.events.amqp;
+
+import static org.assertj.core.api.Assertions.*;
+
+import lombok.RequiredArgsConstructor;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.amqp.core.Binding;
+import org.springframework.amqp.core.BindingBuilder;
+import org.springframework.amqp.core.FanoutExchange;
+import org.springframework.amqp.core.Queue;
+import org.springframework.amqp.rabbit.core.RabbitAdmin;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.testcontainers.service.connection.ServiceConnection;
+import org.springframework.context.ApplicationEventPublisher;
+import org.springframework.context.annotation.Bean;
+import org.springframework.modulith.ApplicationModuleListener;
+import org.springframework.modulith.events.Externalized;
+import org.springframework.transaction.annotation.Transactional;
+import org.testcontainers.containers.RabbitMQContainer;
+import org.testcontainers.utility.DockerImageName;
+
+/**
+ * Integration tests for RabbitMQ-based event publication.
+ *
+ * @author Oliver Drotbohm
+ */
+@SpringBootTest
+class RabbitEventPublicationIntegrationTests {
+
+	@Autowired TestPublisher publisher;
+	@Autowired RabbitAdmin rabbit;
+
+	@SpringBootApplication
+	static class TestConfiguration {
+
+		@Bean
+		@ServiceConnection
+		RabbitMQContainer rabbitMqContainer() {
+			return new RabbitMQContainer(DockerImageName.parse("rabbitmq"));
+		}
+
+		@Bean
+		TestPublisher testPublisher(ApplicationEventPublisher publisher) {
+			return new TestPublisher(publisher);
+		}
+
+		@Bean
+		TestListener testListener() {
+			return new TestListener();
+		}
+	}
+
+	@Test
+	void publishesEventToRabbitMq() throws Exception {
+
+		var target = new FanoutExchange("target");
+		rabbit.declareExchange(target);
+
+		var queue = new Queue("queue");
+		rabbit.declareQueue(queue);
+
+		Binding binding = BindingBuilder.bind(queue).to(target);
+		rabbit.declareBinding(binding);
+
+		publisher.publishEvent();
+
+		Thread.sleep(200);
+
+		var info = rabbit.getQueueInfo("queue");
+
+		assertThat(info.getMessageCount()).isEqualTo(1);
+	}
+
+	@Externalized("target")
+	static class TestEvent {}
+
+	@RequiredArgsConstructor
+	static class TestPublisher {
+
+		private final ApplicationEventPublisher events;
+
+		@Transactional
+		void publishEvent() {
+			events.publishEvent(new TestEvent());
+		}
+	}
+
+	static class TestListener {
+
+		@ApplicationModuleListener
+		void on(TestEvent event) {}
+	}
+}

spring-modulith-events/spring-modulith-events-amqp/src/test/resources/application.properties

@@ -0,0 +1,2 @@
+spring.artemis.embedded.topics=target
+spring.modulith.events.jdbc.schema-initialization.enabled=true