GH-103 - Introduce ApplicationModuleInitializer.

Application modules can now declare instances of ApplicationModuleInititalizer to execute code upon an ApplicationStartedEvent.

This is achieved by registering a corresponding ApplicationListener in SpringModulithRuntimeAutoConfiguration to invoke all instances of AMI sorted via the Comparator introduced in GH-102. To make sure that the invocation order follows topological order, the runtime module strongly depends on JGraphT.

spring-modulith-api/src/main/java/org/springframework/modulith/ApplicationModuleInitializer.java

@@ -0,0 +1,34 @@
+/*
+ * 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;
+
+import org.springframework.boot.context.event.ApplicationStartedEvent;
+
+/**
+ * An interface to be implemented by Spring components that are supposed to be initialized on
+ * {@link ApplicationStartedEvent}. They're {@link ApplicationModule} specific as they're executed in the order
+ * determined by the dependencies of a module. In other words, {@link ApplicationModuleInitializer} of fundamental
+ * application modules are executed first, followed by the ones that depend on it.
+ *
+ * @author Oliver Drotbohm
+ */
+public interface ApplicationModuleInitializer {
+
+	/**
+	 * Run business logic that's needed to initialize the {@link ApplicationModule}.
+	 */
+	void initialize();
+}