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-examples/spring-modulith-example-kafka/src/test/java/example/TestApplication.java

@@ -0,0 +1,66 @@
+/*
+ * 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 example;
+
+import static org.mockito.ArgumentMatchers.*;
+import static org.mockito.Mockito.*;
+
+import example.order.Order;
+import example.order.OrderManagement;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Primary;
+import org.springframework.kafka.core.KafkaOperations;
+
+/**
+ * @author Oliver Drotbohm
+ */
+@SpringBootApplication
+public class TestApplication {
+
+	private static final Logger logger = LoggerFactory.getLogger(TestApplication.class);
+
+	@Bean
+	@Primary
+	@SuppressWarnings("unchecked")
+	KafkaOperations<?, ?> kafkaOperations() {
+
+		var mock = mock(KafkaOperations.class);
+
+		when(mock.send(any(), any())).then(invocation -> {
+
+			logger.info("Sending message {} to {}.", invocation.getArguments()[1], invocation.getArguments()[0]);
+
+			return null;
+		});
+
+		return mock;
+	}
+
+	public static void main(String[] args) {
+
+		var orders = SpringApplication.run(TestApplication.class, args)
+				.getBean(OrderManagement.class);
+
+		logger.info("Triggering order completion…");
+
+		orders.complete(new Order());
+	}
+}